Class 2 Serial Data

U.S. Federal regulations require that all of the automobile manufacturers establish a common communications system. General Motors utilizes the class 2 communications system. Each bit of information can have one of two lengths: long or short. This allows the vehicle wiring to be reduced by the transmission and the reception of the multiple signals over a single wire. The messages that are carried on class 2 data streams are also prioritized. In other words, if two messages attempt to establish any communications on the data line at the same time, only the message with higher priority will continue. The device with the lower priority message must wait. The most significant result of this regulation is that the regulation provides the scan tool manufacturers with the capability of accessing data from any make or model vehicle sold in the United States.

ISO Keyword Protocol 2000 Serial Data

Regulations require that all automobile manufacturers establish a common communications system. The Catera uses International Organization for Standardization (ISO) Keyword Protocol 2000 serial data. This system utilizes a single wire bi-directional data line between the engine control module (ECM), the transmission control module (TCM) and the scan tool. With this type of communication, a voltage level of less than 20 percent of B+ on the data line is considered a logic 0. A voltage level that is more than 80 percent of B+ is considered a logic 1. The message structure is a request and response arrangement that has some similarities to the UART system.

The Diagnostic Executive

The diagnostic executive is a unique segment of software which is designed to coordinate and prioritize the diagnostic procedures as well as define the protocol for recording and displaying their results. The main responsibilities of the diagnostic executive are:

On Board Diagnostic Tests

A diagnostic test is a series of steps which has a beginning and an end. The result of this diagnostic test is a pass or fail that is reported to the diagnostic executive. When a diagnostic test reports a pass result, the diagnostic executive records the following data:

When a diagnostic test reports a fail result, the diagnostic executive records the following data:

Trip

The ability for a diagnostic test to run depends largely upon whether or not a trip has been completed. A trip for a particular diagnostic is defined as vehicle operation, followed by an engine OFF period of duration and driving mode such that any particular diagnostic test has had sufficient time to complete at least once. The requirements for trips vary as the trips may involve items of an unrelated nature, such as the driving style, the length of trip, the ambient temperature, etc. Some diagnostic tests run only once per trip, e.g. catalyst monitor, while other diagnostic tests run continuously, e.g. misfire and fuel system monitors. If the proper enabling conditions are not met during that ignition cycle, the tests may not be complete or the test may not have run.

Warm-up Cycle

In addition, the execution of the diagnostic tests may also be bound by the conditions which must comprehend a warm-up cycle. A warm-up cycle consists of an engine start-up and a vehicle operation such that the coolant temperature has risen more than 4°C (40°F) from the start-up temperature, and reached a minimum temperature of 160°F. If this condition is not met during the ignition cycle, the diagnostic may not run.

Diagnostic Information

The diagnostic charts and functional checks are designed in order to locate a malfunctioning circuit or component through a process of logical decisions. The charts are prepared with the requirement that the vehicle functioned correctly at the time of assembly and that there are no multiple faults present.

There is a continuous self-diagnosis on certain control functions. This diagnostic capability is complement by the diagnostic procedures that are contained in this manual. When the control module detects a malfunction, a diagnostic trouble code sets and the malfunction indicator lamp (MIL) illuminates on some applications.

Malfunction Indicator Lamp (MIL)

The malfunction indicator lamp (MIL) is on the instrument panel and has the following functions:

When the MIL remains ON while the engine is running, or when a malfunction is suspected due to a driveability or emissions problem, you must perform the Diagnostic System Check-Engine Controls.

MIL Requests and History Codes

What happens when types A, B, C and D DTCs report failures and passes, and how the MIL responds. Includes the criteria for turning the MIL ON and OFF:

Special Cases Of Type B Diagnostic Tests

Unique to the misfire diagnostic, the diagnostic executive has the capability of alerting the vehicle operator to potentially damaging levels of a misfire. If a misfire condition exists that could potentially damage the catalytic converter as a result of high misfire levels, the diagnostic executive will command the MIL to flash at a rate of once per second during the time that the catalyst damaging misfire condition is present.

The fuel trim and the misfire are special cases of type B diagnostics. Each time that a fuel trim or a misfire malfunction is detected, the engine load, the engine speed, and the engine coolant temperature (ECT) are recorded.

When the ignition is turned OFF, the last reported set of conditions remain stored. During the subsequent ignition cycles, the stored conditions are used as a reference for similar conditions. If a malfunction occurs during two consecutive trips, the diagnostic executive treats the failure as a normal type B diagnostic, and does not use the stored conditions. However, if a malfunction occurs on two non-consecutive trips, the stored conditions are compared with the current conditions. The MIL will then illuminate under the following conditions:

Storing And Erasing Freeze Frame Data

Government regulations require that engine operating conditions are to be captured whenever the MIL illuminates. The data captured is called Freeze Frame data. The Freeze Frame data is very similar to a single record of operating conditions. Whenever the MIL is illuminated, the corresponding record of operating conditions is recorded to the Freeze Frame buffer.

Each time a diagnostic test reports a failure, the current engine operating conditions are recorded in the Freeze Frame buffer. A subsequent failure will update the recorded operating conditions. The following operating conditions for the diagnostic test which failed will typically include the following parameters:

The Freeze Frame data can only be overwritten with data associated with a misfire or a fuel trim malfunction. Data from these faults take precedence over data that is associated with any other fault. The Freeze Frame data will not be erased unless the associated history DTC is cleared.

Intermittent Malfunction Indicator Lamp

In the case of an intermittent fault the MIL may illuminate, and then after three trips go OFF. However, the corresponding diagnostic trouble code will store in the memory. When unexpected diagnostic trouble codes appear, check for an intermittent malfunction.

A diagnostic trouble code may reset. Consult the Diagnostic Aids that associate with the diagnostic trouble code. A physical inspection of the applicable sub-system will most often resolve the problem.

Data Link Connector (DLC)

The provision for communicating with the control module is the data link connector (DLC). The DLC is usually under the instrument panel (IP). The DLC connects to a scan tool. Some common uses of the scan tool are listed below:

Control Module Learning Ability

The control module has a learning ability which allows for making corrections for minor variations in the fuel system in order to improve the driveability. If the battery cable is disconnected, the learning process resets. A change may be noted in the vehicles performance.

Reprogramming (Flashing) The Control Module

Some vehicles allow reprogramming of the control module without the removal from the vehicle. This provides a flexible and a cost-effective method of making changes in software and calibrations. The service programming system (SPS) will not allow for incorrect software programming or incorrect calibration changes.

Refer to the latest Techline information on the reprogramming or the flashing procedures.

Clearing Diagnostic Trouble Codes

Notice: Turn off the ignition key when disconnecting or reconnecting battery power in order to prevent system damage.

To clear the diagnostic trouble codes (DTCs), ONLY use the diagnostic scan tool Clear DTCs or Clear Info function. When clearing the DTCs, follow the instructions that are supplied by the tool manufacturer.

DTC Modes

On OBD II passenger cars there are five options available in the scan tool DTC mode in order to display the enhanced information available. A description of the new modes, the DTC Info, and the Specific DTC follows. After selecting the DTC, the following menu appears:

The following is a brief description of each of the sub menus in the DTC Info and the Specific DTC. The order in which the sub menus appear here is alphabetical and not necessarily the way that the sub menus will appear on the scan tool.

DTC Info Mode

Use the DTC Info mode in order to search for a specific type of stored DTC information. There are seven choices. The service manual may instruct the technician to test for the DTCs in a certain manner. Always follow the published service procedures.

In order to receive a complete description of any status, press the Enter key before pressing the desired F-key. For example, pressing enter, an F-key will display a complete, spelled out version, of the abbreviated scan tool status.

DTC Status

This selection will display any DTCs that did not run during the current ignition cycle or have reported a test failure during this ignition up to a maximum of 33 DTCs. The DTC tests which run and pass will cause that DTC number to be removed from the scan tool screen.

Fail This Ign. (Fail This Ignition)

This selection will display all of the DTCs that have failed during the present ignition cycle.

History

This selection will display only the DTCs that are stored to the control modules history memory. The history memory will not display Type B DTCs that have not yet requested by the MIL. The history memory will display all of the type A DTCs and the type B DTCs that have requested the MIL and that have failed within the last 40 warm-up cycles. In addition, the history memory will display all of the type C DTCs that have failed within the last 40 warm-up cycles.

Last Test Fail

This selection will display only DTCs that have failed the last time the test ran. The last test may have ran during a previous ignition cycle if an A type or B type DTC is displayed. For type C DTCs, the last failure must have occurred during the current ignition cycle in order to appear as the Last Test Fail.

MIL Request

This selection will display only the DTCs that are requesting the MIL. Type C DTCs cannot be displayed by using this option. This selection will report type B DTCs only after the MIL has been requested.

Not run SCC (Not Run Since Code Clear)

This option will display up to 33 DTCs that have not run since the DTCs were last cleared. Since any displayed DTCs have not run, their condition, passing or failing, is unknown.

Test Fail SCC (Tested Failed Since Code Clear)

This selection will display all of the active DTCs and the history DTCs that have reported a test failure since the last time that the DTCs were cleared. The DTCs that last failed more than 40 warm-up cycles before this option is selected will not be displayed.

Specific DTC Mode

This mode is used in order to check the status of the individual diagnostic tests by the DTC number. You can access the selection if a DTC has passed, if a DTC has failed, or both. Many OBD II DTC mode descriptions are possible because of the extensive amount of information that the diagnostic executive monitors regarding each test.

This selection will only allow the entry of the DTC numbers that are supported by the vehicle being tested. If an attempt is made to enter the DTC numbers for tests which the diagnostic executive does not recognize, the requested information will not be displayed correctly and the scan tool may display an error message. This also applies to using the DTC trigger option in the Snapshot mode. If an invalid DTC is entered, the scan tool will not trigger.

Failed Last Test

This message displayed indicates that the last diagnostic test failed for the selected DTC. For type A DTCs and type B DTCs, this message will be displayed during subsequent ignition cycles until the test passes or the DTCs are cleared. For the type C DTCs, this message will clear whenever the ignition is cycled.

Failed Since Clear

This message displayed indicates that the DTC has failed at least once within the last 40 warm-up cycles since the last time that the DTCs were cleared.

Failed This Ign. (Failed This Ignition)

This message displayed indicates that the diagnostic test has failed at least once during the current ignition cycle. This message will clear when the DTCs are cleared or when the ignition is cycled.

History DTC

This message displayed indicates that the DTC has been stored to memory as a valid fault. A DTC displayed as a History fault does not necessarily mean that the fault is no longer present. The history description means that all of the conditions that are necessary for reporting a fault have been met, maybe even currently, and the information was stored to the control module memory.

MIL Requested

This message displayed indicates that the DTC is currently causing the MIL to be turned ON. Remember that only type A and B DTCs can request the MIL. The MIL request cannot be used in order to determine if the DTC fault conditions are currently being experienced. This is because the diagnostic executive will require up to 3 trips during which the diagnostic test passes to turn OFF the MIL.

Not Run Since Cl (Not Run Since Cleared)

This message displayed indicates that the selected diagnostic test has not run since the last time DTCs were cleared. Therefore, the diagnostic test status, passing or failing, is unknown. After DTCs are cleared, this message will continue to be displayed until the diagnostic test runs.

Not Run This Ign. (Not Run This Ignition)

This message displayed indicates that the selected diagnostic test has not run yet this ignition cycle.

Test Ran and Passed

This message displayed indicates that the selected diagnostic test has:

If the indicated status of the vehicle is Test Ran and Passed after a repair verification, the vehicle is ready to be released to the customer.

If the indicated status of the vehicle is Failed This Ign. after a repair verification, then repair is incomplete and further diagnosis is required.

Prior to repairing a vehicle, you can use the status information in order to evaluate the state of the diagnostic test, and to help to identify an intermittent problem. The technician can conclude that although the MIL is illuminated, the fault condition that caused the DTC to set is not present. An intermittent condition must be the cause.

System Status and Drive Cycle For Satisfying Federal Inspection/Maintenance (I/M 240) Regulations

Important: The System Status display indicates only whether or not the test has been completed and does not necessarily mean that the test has passed. If a Failed Last Test indication is present for a DTC that is associated with one of the above systems, this indicates that the test is failed and that the diagnosis and repair is necessary in order to meet the I/M 240 requirement. Verify that the vehicle passes all of the diagnostic tests that are associated with the displayed System Status prior to returning the vehicle to the customer. Refer to the Typical OBD-II Drive Cycle graphic, more than one drive cycle may be needed, to use as a guide in order to complete the I/M 240 System Status tests.

The System Status selection is included in the scan tool System Info menu.

Several states require that the I/M 240, OBD ll system, pass several on-board tests for the major diagnostics prior to having a vehicle emission inspection. This is also a requirement to renew license plates in some areas.

Using a scan tool, the technician can observe System Status, complete or not complete, in order to verify that the vehicle meets the criteria to comply with local area requirements. Using the System Status display, any of the following systems or a combination of the systems may be monitored for I/M readiness:

Following a DTC info clear, System Status will clear only for the systems that are affected by any DTCs that are stored. Following a battery disconnect or an ECM replacement, all of the System Status information will clear.

Typical OBD II Drive Cycle

Total time of OBD II Drive Cycle 12 minutes. Cold Start, coolant temperature less than 50°C (122°F).
Vehicle Drive Status	What is Monitored?
Idle 2.5 minutes in Drive (Auto) Neutral (Man), A/C and rear defogger ON	HO2S Heater, Misfire, Secondary Air, Fuel Trim, EVAP Purge
A/C off, accelerate to 90 km/h (55 mph), 1/2 throttle.	Misfire, Fuel Trim, Purge
3 minutes of Steady State - Cruise at 90 km/h (55 mph)	Misfire, EGR, Secondary Air, Fuel Trim, HO2S, EVAP Purge
Clutch engaged (Man), no braking, decelerate to 32 km/h (20 mph)	EGR, Fuel Trim, EVAP Purge
Accelerate to 90-97 km/h (55-60 mph), 3/4 throttle	Misfire, Fuel Trim, EVAP Purge
5 minutes of Steady State Cruise at 90-97 km/h (55-60 mph)	Catalyst Monitor, Misfire, EGR, Fuel Trim, HO2S, EVAP Purge
Decelerate, no breaking. End of Drive Cycle	EGR, EVAP Purge

Primary System Based Diagnostics

There are primary system based diagnostics which evaluate the system operation and the effect that the system operation has on the vehicle emissions. The primary system based diagnostics are listed below with a brief functional description of the diagnostic.

Oxygen Sensor Diagnosis

The fuel control heated oxygen sensor (HO2S 1) is diagnosed for the following conditions:

The catalyst monitor heated oxygen sensor (HO2S 2) is diagnosed for the following functions:

HO2S Heater

Heated oxygen sensors (HO2S) are used in order to minimize the amount of time required to obtain a Closed Loop fuel control operation. The sensors also allow for accurate catalyst monitoring. The oxygen sensor heater greatly decreases the amount of time that is required for fuel control sensor HO2S 1 to become active. The oxygen sensor heater also allows the catalyst monitor HO2S 2 to maintain a sufficiently high temperature to ensure accurate exhaust oxygen content readings from the engine.

Catalyst Monitor Heated Oxygen Sensor (HO2S 2)

A 3-way catalytic converter (TWC) is used In order to control the emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction that oxidizes the HC and the CO that are present in the exhaust gases, converting the gases into harmless water vapor and carbon dioxide. The catalyst also reduces and converts the NOx into nitrogen. The ECM monitors this process by using the HO2S 1 and the HO2S 2 . The HO2S 1 produces an output signal that indicates how much oxygen is present in the exhaust gas entering the TWC. The HO2S 2 produces an output signal that indicates the oxygen storage capacity of the catalyst. The HO2S 2 signal is thus an indicator of the catalysts ability to convert the exhaust gases efficiently.

In addition to the catalyst monitoring, the HO2S 2 has a limited role in controlling the fuel delivery. If the HO2S 2 signal indicates a high oxygen content or a low oxygen content for an extended period of time while in a Closed Loop operation, the ECM will adjust the fuel delivery slightly in order to compensate for this condition.

If the oxygen sensor pigtail wiring, the connector, or the terminal are damaged, the entire oxygen sensor assembly must be replaced. DO NOT attempt to repair the wiring, the connector, or the terminals. The sensors must have a clean air reference in order to function properly. This clean air reference is obtained by way of the oxygen sensor wires. Attempting to repair the wires, the connectors, or the terminals can result in the obstruction of the air reference and degrade the oxygen sensor performance.

Catalyst Monitor Diagnostic Operation

The OBD II catalyst monitor diagnostic measures the oxygen storage capacity of the catalyst. In order for this process to happen, the heated sensors are installed before and after the TWC. The voltage variations between the sensors allow the control module to determine the catalysts emission performance. As a catalyst becomes less effective in promoting any chemical reactions, the catalysts capacity to store and release oxygen generally degrades. The OBD II catalyst monitor diagnostic is based on a correlation between the conversion efficiency and the oxygen storage capacity of the catalyst. A good catalyst, e.g. 95 percent hydrocarbon conversion efficiency, will show a relatively flat output voltage on the post-catalyst (HO2S 2). A degraded catalyst, (65 percent hydrocarbon conversion, will show greatly increased activity in the output voltage from the post-catalyst (HO2S 2).

The post-catalyst HO2S measures the oxygen storage and release capacity of the catalyst. A high oxygen storage capacity indicates a good catalyst, and a low oxygen storage capacity indicates a failing catalyst. In order to achieve accurate oxygen sensor voltage readings like those shown in the post-catalyst HO2S outputs graphic, the TWC and the HO2S 2 must be at the normal operating temperature.

The catalyst monitor diagnostic is sensitive to the following conditions:

Exhaust system leaks may cause the following results:

Some of the contaminants that may be encountered are phosphorus, lead, silica, and sulfur. The presence of these contaminants at any HO2S will prevent the TWC diagnostic from functioning properly.

Three-Way Catalyst Oxygen Storage Capacity

The TWC must be monitored for efficiency. In order to accomplish this process, the control module monitors the pre-catalyst HO2S and the post-catalyst HO2S . When the TWC is operating properly, the post-catalyst oxygen sensor (2) will have significantly less activity than the pre-catalyst oxygen sensor (1).

The TWC stores and releases oxygen as needed during the normal reduction and oxidation process. The control module calculates the catalysts oxygen storage capacity by comparing the pre-catalyst (1) and post catalyst (2) oxygen sensors voltage levels. If the activity of the post-catalyst oxygen sensor approaches that of the pre-catalyst oxygen sensor, the catalysts efficiency is degraded.

The stepped or staged testing levels allow the control module to statistically filter the test information, which keeps the oxygen storage capacity test results accurate. The calculations that are performed by the on-board diagnostic system are very complex. For this reason, do not use the post-catalyst oxygen sensor activity in order to determine the oxygen storage capacity unless you are directed by the service manual.

The efficiency of the catalyst is monitored in two stages. Failure of the first stage is an indication that the catalyst requires further testing. During the second stage, the inputs from the pre-catalyst HO2S and the post-catalyst HO2S are examined more closely in order to determine if the catalyst is indeed degraded. This additional statistical processing increases the accuracy of the oxygen storage capacity monitoring. Failing the first, stage 1, test does not indicate a failed catalyst. The catalyst may be marginal or the fuel sulfur content could be very high.

Aftermarket HO2S characteristics may be different from the original equipment manufacturers sensor. These differences may lead to a false pass or a false fail of the catalyst monitor diagnostic. Similarly, if an aftermarket catalyst does not contain the same amount of cerium as the original part, the correlation between the oxygen storage and the conversion efficiency may be altered enough to set a false DTC.

Misfire Monitor Diagnostic Operation

The misfire monitor diagnostic is based on crankshaft rotational velocity, reference period, variations. The control module determines the crankshafts rotational velocity by using the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor. When a cylinder misfires, the crankshaft slows down momentarily. By monitoring the CKP and CMP sensor signals, the control module can calculate when a misfire occurs.

For a non-catalyst damaging misfire, the diagnostic will report the misfire within 1,000-3,200 engine revolutions.

For catalyst damaging misfire, the diagnostic will respond to the misfire within 200 engine revolutions.

Rough roads may cause a false misfire detection. A rough road will cause torque to apply to the drive wheels and the drive train. This torque can intermittently decrease the crankshaft rotational velocity. This may be detected as a false misfire.

On automatic transaxle equipped vehicles, the torque converter clutch (TCC) will be disabled whenever a misfire is detected. Disabling the TCC isolates the engine from the rest of the drive line and minimizes the effect of the drive wheel inputs on the crankshaft rotation.

When the TCC has been disabled as a result of a misfire detection, the TCC will re-enable after approximately 3,200 engine revolutions if no further misfire is detected. The TCC will remain disabled whenever a misfire is detected. This allows the misfire diagnostic to re-evaluate the system.

During a transaxle high fluid temperature condition, the misfire diagnostic will be disabled and the TCC will operate normally. This avoids further increasing the temperature of the transaxle.

Misfire Counters

Whenever a cylinder misfires, the misfire diagnostic counts the misfire and notes the crankshaft position at the time when the misfire occurred. The misfire counters are basically a file on each engine cylinder. A current and a history misfire counter is maintained for each cylinder. The misfire current counters, Misfire Cur #1-6, indicate the number of firing events out of the last 200 crankshaft revolutions that were misfires. The misfire current counters will display real time data without a misfire DTC being stored. The misfire history counters, Misfire History #1-6, indicate the total number of cylinder misfires. The misfire history counters will display 0 until the misfire diagnostic fails and a DTC P0300 is set. Once the misfire DTC sets, the misfire history counters will be updated every 200 crankshaft revolutions.

The misfire counters graphic illustrates how these misfire counters are maintained. If the misfire diagnostic reports a failure, the diagnostic executive reviews all of the misfire counters before reporting a DTC. This way, the diagnostic executive reports the most current information.

When crankshaft rotation is erratic, a misfire condition will be detected. Because of this erratic condition, the data that is collected by the diagnostic can sometimes incorrectly identify which cylinder is misfiring. The misfire counters graphic shows misfires counted from more than one cylinder. Cylinder #1 has the majority of counted misfires. In this case, the misfire counters would identify cylinder #1 as the misfiring cylinder. The misfires in the other counters were just background noise caused by the erratic rotation of the crankshaft. If the number of accumulated misfires is sufficient for the diagnostic to identify a true misfire, the diagnostic will set DTC P0300--Misfire Detected.

Use the Techline equipment in order to monitor the misfire counter data on the OBD ll compliant vehicles. Knowing which specific cylinders misfired can lead to the root cause, even when dealing with a multiple cylinder misfire. Using the information in the misfire counters, identify which cylinders are misfiring.

Misfire counter information is located in the Specific Eng. menu, Misfire Data sub-menu of the data list.

The misfire diagnostic may identify a temporary fault not necessarily caused by a vehicle emission system malfunction. Examples of this include the following items:

Fuel Trim System Monitor Diagnostic Operation

This system monitors the averages of short-term and long-term fuel trim values. If these fuel trim values stay at their limits for a calibrated period of time, a malfunction is indicated. The fuel trim diagnostic compares the averages of short-term fuel trim values and long-term fuel trim values to rich and lean thresholds. If either value is within the thresholds, a pass is recorded. If both values are outside of their thresholds, a rich or a lean DTC will record.

In order to meet OBD ll requirements, the control module uses weighted fuel trim cells in order to determine the need to set a fuel trim DTC. A fuel trim DTC can only set if the fuel trim counts in the weighted fuel trim cells exceed specifications. This means that the vehicle could have a fuel trim problem which is causing a concern under certain conditions, for example, engine idle high due to a small vacuum leak or an engine idle rough due to a large vacuum leak, while the engine operates normal at other times. No fuel trim DTC would set, although an engine idle speed DTC or a heated oxygen sensor (HO2S) DTC may set. Remember, use a scan tool in order to observe the fuel trim counts while the problem is occurring.

Remember, a fuel trim DTC may be triggered by a list of vehicle faults. Make use of all of the information available, other DTCs stored, a rich or a lean condition, etc., when diagnosing a fuel trim fault.

Comprehensive Component Monitor Diagnostic Operation

Comprehensive component monitoring diagnostics are required in order to monitor the emissions-related input and output powertrain components. The CARB OBD II Comprehensive Component Monitoring List Of Components Intended To Illuminate The MIL is a list of components, features, or functions that could fall under this requirement.

Input Components

Input components are monitored for circuit continuity and out-of-range values. This monitoring includes rationality checking. Rationality checking means a fault will be indicated when the signal from a sensor does not seem reasonable. For example, a throttle position (TP) sensor that indicates a high throttle position angle at low engine loads or speeds is irrational. The input components may include, but are not limited to the following sensors:

In addition to the circuit continuity and rationality check, the ECT sensor is monitored for the sensors ability to achieve a steady state temperature in order to enable a Closed Loop fuel control.

Output Components

The output components are diagnosed for a proper response in order to control the module commands. Any components, where functional monitoring is not feasible, will be monitored for circuit continuity and out-of-range values, if applicable.

The output components to be monitored include, but are not limited to the following circuits:

California Air Resources Board (CARB) OBD II Comprehensive Component Monitoring List of Components Intended to Illuminate MIL

Important: Not all vehicles have these components: