PCM Data Description

The following information will assist in diagnosing emission or driveability problems. The technician can view the displays while driving the vehicle. Refer to Powertrain On Board Diagnostic (OBD) System Check in engine controls for additional information.

The displayed data messages on the scan tool are divided into the Engine, the Specific Engine, and the DTC lists as follows:

Engine Data

Specific Engine Data

DTC Data

Engine Scan Tool Data Definitions

A/C High Side Pressure--Range 0-5.0 Volts: The A/C High Side displays the pressure value of the A/C refrigerant pressure sensor. The A/C High Side helps diagnose the DTC P0530.

A/C High Side Pressure--Range 0-459 PSI (0-3100 kPa): The A/C High Side displays the pressure value of the A/C refrigerant pressure sensor. The A/C High Side helps diagnose the DTC P0530.

Another TWC Test Desired--Range Yes/No: The display shows Yes or No. The display indicates if another catalyst test is needed for a catalyst test decision. The PCM may need another test to determine if the catalyst is operating properly.

A/C Relay--Range Off/On: The A/C Relay represents the commanded state of the A/C clutch control relay. The A/C clutch should be engaged when the scan tool displays ON.

A/C Request--Range Yes/No: A/C Request--This displays if PCM has received an A/C request from body control module (BCM) YES or NO.

Adaptive Knock Retard--Range 0-90 degrees: The Adaptive Knock Retard indicates the long term amount of the spark advance the PCM removes from the ignition control (IC). The PCM responds to the knock sensor (KS) signal.

Air Fuel Ratio--Range 0:1-25.5:1: The air fuel ratio indicates the air to fuel ratio based on the oxygen sensor (O2S 1) inputs. The PCM uses the fuel trims to adjust fueling in order to attempt to maintain an air fuel ratio of 14.7:1.

BARO--Range 11-105 kPa: The barometric pressure (BARO) sensor measures the change in the intake manifold pressure which results from altitude changes. This value is updated at ignition ON and also at wide open throttle (WOT).

Base PWM Cyl. 1-4--Range 0-999.9 mS: Indicates the base pulse width modulation (PWM) or ON time of the indicated cylinder injector in milliseconds. When the engine load is increased, the injector pulse width will increase.

Calc. Air Flow--Range 0-512 grams/second: The calculated air flow is a calculation based on manifold absolute pressure. The calculation is used in several diagnostics to determine when to run.

Calc. Vacuum--Range 0-80 kPa/PSI: The display shows the calculated vacuum which is an indication of engine load. The calculated vacuum is the difference between the BARO reading and the MAP sensor reading. The lower the Calc. Vacuum value, the higher the engine load.

Calc. Convertor Temp.--Range 300-1000°C (572-1832°F): Display shows temperature in degrees C and degrees F from 0°C (32°F) to 765°C (1409°F). This parameter is the PCM calculated temperature of the three-way catalyst.

CKP Active Counter (7X Reference)-- Range 0-255 Counts: The crankshaft position (CKP) activity counter displays whether the PCM is receiving the 7X sync pulses from the ignition module. Helpful in diagnosing DTC P0335 and Cranks But Will Not Run conditions.

CMP Active Counter--Range 0-255 Counts: The Camshaft Position (CMP) activity counter displays the activity sent to the PCM from the CMP sensor. The counter will continually increment while the engine is running. The CMP Act. Counter is helpful in diagnosing the DTC P0342.

CMP Resync Counter--Range 0-255 Counts: The camshaft position (CMP) resync counter displays the number of times the PCM had to resync with the CMP sensor. The CMP resync counter is helpful in diagnosing the DTC P0341.

Cruise--Range Disable/Enabled: The Stepper Cruise display indicates if the PCM is allowing the cruise operation. The PCM has the ability to disable the cruise control under certain conditions.

Cruise--Range Engaged/Disengaged: Cruise engaged is an input from the cruise control module to the PCM and indicates if the cruise control system is in control of vehicle speed. The PCM uses this information to change transmission shift calibrations and to turn ON an indicator lamp on the instrument panel cluster (IPC) (when equipped). Refer to Diagnostic System Check - Cruise Control in Cruise Control.

Current TWC Test Complete--Range Yes/No: The display shows Yes or No. This display indicates that at least one pass or fail test decision has been made during the idle catalyst test (P0420). It takes only one test to obtain a pass decision, but it may take six tests to obtain a fail decision.

Desired Idle Speed--0-3187 RPM: The PCM commands the idle speed. The PCM compensates for various engine loads in order to maintain the desired idle speed. The actual engine RPMs speed should remain close to the desired idle under the various engine loads with the engine idling.

ECT--Range -40°C-151°C (-40°F-304°F): The engine coolant temperature (ECT) sensor sends engine temperature information to the PCM. The PCM supplies 5 volts to the engine coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the PCM monitors a high voltage which it interprets as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal will decrease and the PCM will interpret the lower voltage as a warm engine.

Engine Coolant Low--Range Low/OK: The engine coolant level (ECL) is displayed as Low or OK. The ECL indicates whether the coolant in the radiator surge tank is Low or OK.

Engine LOAD--Range 0-100 Percent: Indicates engine load based on manifold absolute pressure. The higher the percentage, the more load the engine is under.

Engine Oil Pressure--Range Low/OK: The engine oil pressure switch sends an input to the PCM to indicate whether the engine oil pressure is Low or OK.

Engine Run Time--Range 0:00:00-18:12:15 hours:minutes:seconds: The engine run time is a measure of how long the engine has been running. When the engine stops running, the timer resets to zero.

Engine Speed--Range 0-6384 RPM: Engine speed is computed by the PCM from the fuel control reference input. It should remain close to desired idle under the various engine loads with the engine idling.

EVAP Canister Purge--Range 0-100 Percent: The evaporative emission (EVAP) purge valve solenoid is a proportional signal used in order to control the evaporative emission canister purge function. At 0 percent the valve is commanded fully closed. 100 percent implies that the valve is fully open.

EVAP Vent Solenoid--Range Open/Closed: The EVAP vent solenoid allows fresh outside air to the EVAP canister during the purge mode. The EVAP vent solenoid allows the diagnostic to pull a vacuum on the fuel tank by closing the vent solenoid.

Fan Control Relay 1--Range Off/On: The fan control (FC) relay is commanded by the PCM. FC relay 1 displays the command as On or OFF.

Fuel Pump Relay Command--Range Off/On: The Fuel Pump Relay is commanded by the PCM. When the ignition is on the PCM supplies voltage to the Fuel pump relay which supplies voltage to the Fuel pump and Fuel Injectors.

Fuel Tank Pressure--Range -25.89-32.45 mm hg: The fuel tank pressure sensor measures the difference between the pressure or the vacuum in the fuel tank and the outside air pressure. When the air pressure in the fuel tank equals the outside air pressure, the output voltage of the sensor is 1.3 to 1.7 volts.

Fuel Tank Pressure--Range - 0.0-5.0 Volts: The fuel tank pressure sensor measures the difference between the pressure or the vacuum in the fuel tank and the outside air pressure. When the air pressure in the fuel tank equals the outside air pressure, the output voltage of the sensor is 1.3 to 1.7 volts.

Fuel Level Sensor Range--0 Percent- -100 Percent: The fuel level sensor monitors the fuel level in the tank. Several of the Enhanced EVAP system diagnostics are dependent upon the correct fuel level reading.

Fuel Trim Cell--Range 0-22: A Fuel Trim Cell depends upon the engine speed and the MAP sensor readings. RPM vs. MAP is broken down into 22 fuel trim cells. The Fuel Trim Cell indicates which cell is currently active.

FT Index--Range 0-255 (-100-100 Percent): Fuel Trim (FT) Index represents the average Long Term Fuel Trim for certain cells which are used in determining DTC P0171 and P0172.

GEN L Terminal--Range Inactive/Active: The generator L terminal indicates whether the PCM is allowing the generator to operate. The PCM can disable the generator under certain conditions to ease starting. Inactive indicates that the PCM is allowing generator operation, while active indicates that the PCM is not allowing generator operation.

GEN PWM--Range 0-100 Percent: The generator F terminal is the duty cycle or load input to the PCM from the generator. As the generator load increases, the PCM will adjust idle speed accordingly.

HO2S 2--Range 0-1132 mV: The rear heated oxygen sensor (HO2S 2) represents the exhaust oxygen output voltage past the catalytic converter. This voltage remains inactive, or the voltage will appear lazy within a range of 100 mV (lean exhaust) and 900 mV (rich exhaust) when the system is operating in a Closed Loop.

IAC Position--Range 0-255 Counts: The idle air control (IAC) pintle position command from the PCM is displayed in counts. The higher the counts read, the greater the commanded idle speed is. The idle air control responds fairly quickly to changes in the engine load in order to maintain the desired idle RPM.

IAT--Range -40°C-151°C (-40°F-304°F): The PCM converts the resistance of the intake air temperature (IAT) sensor to degrees in the same manner as the ECT sensor. Intake air temp is used by the PCM to adjust fuel delivery and spark timing according to incoming air density.

Ignition 1--Range 0-25.5 volts: The ignition volts represents the system voltage measured by the PCM at the ignition feed circuit.

KS Noise Channel--Range 0-5 volts: The KS noise channel indicates when the PCM detects the knock sensor (KS) signal. The PCM should display close to 1.0 volt at idle.

KS Retard--0-90 degrees: The knock sensor (KS) retard indicates the amount of spark advance (IC) the PCM is removing from in response to the knock sensor (KS) signal.

Lean/Rich Transition--Range 0-255 counts: The PCM counts the number of times the oxygen sensor (O2S 1) goes from a low voltage (lean exhaust) to a high voltage (rich exhaust) within a 100 second period. Lean/Rich transition should increment when the vehicle is operating within the Conditions for Setting in DTC P0133 or DTC P1133.

Lean/Rich Avg.--Range 0-249 mS counts: The PCM takes the Lean/Rich transition times following the completion of the data collection period as specified in the Conditions for Setting in DTC P0133 and DTC P1133. Then the PCM averages the transition time from the total transition times.

Long Term FT--Range 0-255 (-100-100 Percent): The Long Term Fuel Trim (FT) is derived from the short term fuel trim value. The Long Term Fuel Trim (FT) is used for the long term correction of the fuel delivery. A value of the 128 counts (0 percent) indicates that the fuel delivery requires no compensation in order to maintain a 14.7:1 air to fuel ratio. A value below 128 counts means that the fuel system is too rich and the fuel delivery is being reduced. The PCM is decreasing the injector pulse width. A value above 128 counts indicates that a lean condition exists for which the PCM is compensating.

Loop Status--Range Open/Closed: A Closed Loop displayed indicates that the PCM is controlling the fuel delivery according to the oxygen sensor (O2S 1) voltage. The PCM controls the fuel delivery air to fuel ratio as close to 14.7:1 as possible.

MAP - Range 11-105 kPa, 0-5.0 Volts: The manifold absolute pressure (MAP) sensor measures the change in the intake manifold pressure which results from engine load and speed changes. As the intake manifold pressure increases, the air density in the intake also increases and additional fuel is required.

MIL -Scan Tool displays OK, Faulty, or Invalid state: These parameters describe the condition of the Control Circuit.

Misfire Current #1-4--Range 0-255 Counts: Indicates the number of current misfires that are present in the indicated cylinder. Increments only when misfire is current.

Misfire History #1-4--Range 0-255 Counts: Indicates the number of misfires that have occurred after 195 current misfires have been counted. The current misfire counter will add misfires to the history misfire counter after 195 total misfires have taken place. If 1 cylinder is misfiring, the misfiring current counter will have 195 misfires counted before adding to its history counter. If 2 cylinders are misfiring, the misfiring current counters will add to their history counters after 97 misfires. Increments only after a misfire DTC has been set.

Med. Resolution Resync Counter--Range 0-255 Counts: The medium resolution resync counter displays the number of times the PCM had to resync the crankshaft position (CKP) sensor. The med. resolution resync counter is helpful in diagnosing the DTC P0335.

Med. Resolution Engine Sync.--Range YES/NO: The medium resolution engine sync. displays if the PCM is receiving the 7x sync pulse. The med. resolution engine sync. is helpful in diagnosing the DTC P0300 and P0301-P0304.

Number of DTCs: The number of Current DTCs indicates the total number of current diagnostic trouble codes (DTCs) set. These current DTCs set does not necessarily mean that the malfunction indicator lamp (MIL) is illuminated.

Number of Catalyst Mon Test Completed--Range 0 - 255: The Catalyst Mon. Test completed sample counter is the total number of test samples this ignition cycles. The Samples counter should never indicate greater than 1 unless the technician has cleared a DTC or disconnected the battery.

O2S 1--Range 0-1132 mV: The oxygen sensor (O2S 1) reading represents the exhaust oxygen sensor output voltage. This voltage will fluctuate constantly between 100 mV (lean exhaust) to 900 mV (rich exhaust) when operating in a Closed Loop.

Park/Neutral Position Switch--Range Park/Reverse/Neutral/Overdrive/Drive 3/Drive 2/Low/Invalid: The scan tool displays the decoded position of the park/neutral position switch PRNDL inputs. This information is then sent by Class 2 serial data to the instrument panel cluster (IPC) to be displayed to the operator on the IPC. If a valid combination of inputs is not seen by the PCM, Invalid will be displayed.

Park/Neutral Position Switch P, A, B, C--Range High or Low: A transaxle mounted switch is used as an input to let the PCM know what position the gear select lever is in. The scan tool status will switch from High to Low as different combinations are met. In Park, PRNDL P and A will be Low and B and C will be High.

Power Enrichment--Range Active/Inactive: The scan tool indicates when power enrichment mode is active (moderate to heavy acceleration). Helpful in diagnosing DTC  P1171.

Purge Learn Memory--Range 0.00-1.00: The purge learn memory is a display of the PCM adding or subtracting the fuel. The purge learn memory is based on the EVAP purge. This number is added to the fuel trim calculations. The fuel is added or subtracted there. A number near 1 indicates that the fuel is being added to the fuel trim. A number near 0 indicates that fuel is being taken away from the fuel trim.

Rich/Lean Transition--Range 0-255 counts: The PCM counts the number of times the oxygen sensor (O2S 1) goes from a high voltage (rich exhaust) to a low voltage (lean exhaust) within a 100 second period. Rich/Lean transition should increment when the vehicle is operating within the Conditions for Setting in DTC P0133 or DTC P1133.

Rich/Lean Avg.--Range 0-249 mS: The PCM takes the Rich/Lean transition value following the completion of the data collection period as specified in the Conditions for Setting in DTC P0133 and DTC P1133. Then the PCM divides the value with the 100 second period.

Short Term FT--Range 0-255 (-100% to 100%): Short Term Fuel Trim (FT) represents a short term correction to fuel delivery by the PCM in response to the amount of time the oxygen sensor voltage spends above or below the 450 mV threshold. If the oxygen sensor has mainly been below 450 mV, indicating a lean air/fuel mixture, short term fuel trim will increase to tell the PCM to add fuel. If the oxygen sensor voltage stays mainly above the threshold, the PCM will reduce fuel delivery to compensate for the indicated rich condition.

Spark--Range 64 to -64 degrees: This is a display of the spark advance (IC) calculation which the PCM is programming in the ignition system. It computes the desired spark advance using data such as engine temperature, RPM, engine load, vehicle speed, and operating mode.

TCC Brake Switch--Open/Closed: When the brake pedal is applied, the torque converter clutch (TCC) brake switch sends a signal to the PCM to disengage the TCC and disable cruise control.

Total Misfire Current Counter-- Range 0-255 Counts: The Total Misfire indicates the total number of misfires that have been detected in all cylinders after 100 engine cycles. One cycle equals the completion of a 4 stroke cycle. The total misfire only increments during a steady state cruise conditions.

TP Angle--Range 0-100 Percent: The PCM computes the throttle position (TP) from the TP sensor voltage input. The TP angle will auto zero to 0 percent at idle when the TP voltage is below 0.90 volt. The TP angle will read 100 percent at wide open throttle (WOT).

TP Sensor--Range 0.0-5.0 Volts: The PCM uses the throttle position (TP) sensor to determine the amount of the throttle demanded by the operator of the vehicle. The TP sensor reads between 0.36-0.96 volt at idle to above 4.0 volts at wide open throttle (WOT).

Transmission Range Switch P/A/B/C--Scan Tool displays Hight or Low: The Trans Switch P/A/B/C display represents the state of the four inputs from the trans axle range switch. High display indicates battery voltage signal being monitored at the PCM. Low indicates a ground input signal at the PCM.The combination of tranaxle range inputs indicates the position of the transaxle manual valve.

TWC Stage 1 Started--Range Yes/No: The display shows Yes or No. This display indicates that the first air/fuel transition of the idle catalyst test (P0420) is in progress.

TWC Stage 2 Started--Range Yes/No: The display shows Yes or No. This display indicates that the first air/fuel transition of the idle catalyst test (P0420) is in progress.

TWC System Related DTC is Set--Range Yes/No: The display shows Yes or No. This display indicates if a DTC is set that will prevent the idle catalyst test (P0420) from running.

TWC Test Initialization Conditions Met--Range Yes/No: Display shows Yes or No. This display says that the idle conditions required to test the catalyst are met.

TWC Test Enabled--Range Yes/No: The display shows Yes or No. This display indicates the Idle Catalyst Test (P0420) has started to run. There is a 5 second delay between the TWC Test Initilization Conditions Met and the idle catalyst test being enabled.

TWC Warmup Conditions Met--Range Yes/No: Display shows Yes or No. This display says that the warmup conditions required to test the catalyst are met and the catalyst is sufficiently warmed up.

Vehicle Speed--Range 0-255 MPH, 0-255 km/h: The vehicle speed sensor signal is converted into MPH/km/h for display. The vehicle speed output from the PCM is 4000 pulses per mile. The scan tool uses the class 2 serial data from the PCM to obtain vehicle speed, while the instrument panel cluster, cruise control module and multi-function alarm module use the 4000 ppm output.