Circuit Description
The powertrain control module (PCM) controls a Closed Loop air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The PCM monitors the heated oxygen sensor (HO2S) signal voltage and adjusts the fuel delivery based on the signal voltage while in Closed Loop. A change made to the fuel delivery changes the long and short term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltages. These changes fine tune the engine fueling. The long term fuel trim values change in response to trends in the short term fuel trim. The long term fuel trim makes coarse adjustments to fueling in order to re-center and restore control to short term fuel trim. You can use a scan tool in order to monitor the short and long term fuel trim. The ideal fuel trim values are around 0 percent. A positive fuel trim value indicates that the PCM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the PCM is reducing the amount of fuel in order to compensate for a rich condition. If the PCM detects an excessively Rich or Lean condition, the PCM sets a diagnostic trouble code (DTC). The long term fuel trim diagnostic parameter is an average of several of the long term speed load learn cells which the PCM selects based on the engine speed and the engine load.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0200, P0300, P0335, P0336, P0351-P0358, P0410, P0412, P0418, P0443, P0500, P0502, P0503, P1120, P1220, P1221, P1258, P1415, P1416, are not set. |
| • | The Engine Coolant Temperature is between 50°C (122°F) and 115°C (239°F). |
| • | The Fuel trim is enabled. |
| • | The Barometric Pressure is greater than 74 kPa. |
| • | The Mass Air Flow is between 5.0 grams per second and 90 g/s. |
| • | The Manifold Absolute Pressure is between 26 kPa and 90 kPa. |
| • | The Intake Air Temperature is between -20°C (-4°F) and 90°C (194°F). |
| • | The engine speed is between 400 RPM and 3000 RPM. |
| • | The TP Sensor angle is less than 90%. |
| • | The vehicle speed is less than 137 km/h (85 mph). |
| • | All of the above conditions met for 40.0 seconds. |
Conditions for Running the DTC
The PCM detects the average Long Term Fuel Trim cell values are below a predetermined threshold.
Action Taken When the DTC Sets
| • | The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle during which the diagnostic runs and fails if the diagnostic fails under the same conditions such as the load, the RPM, or the temperature, as the previous ignition cycle during which the test ran and failed. |
| • | The first time during which the diagnostic fails, the PCM records the operating conditions in the Failure Records. |
| • | The second consecutive ignition cycle during which this diagnostic fails, under the same conditions such as the load, the RPM, or the temperature, as the previous ignition cycle that the test ran and failed, the PCM stores this information in the Freeze Frame. The PCM copies any data that was previously stored in the Freeze Frame and copies the data into the Failure Records. The PCM then overwrites the Freeze Frame. The only exception to this is if a Misfire DTC was already recorded in the Freeze Frame. In this case, the Misfire data stays in the Freeze Frame and the PCM updates the Fuel Trim data in the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns the MIL OFF after three consecutive ignition cycles during which the diagnostic runs and does not fail within the same conditions that the DTC last failed. |
| Important: If the last failure was during a non-typical driving condition, the MIL may remain ON longer than the three ignition cycles. Review the Freeze Frame/Failure Records for the last failure conditions. |
| • | A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures. |
| • | A last test failed (Current DTC) clears when the diagnostic runs and does not fail. |
| • | Use a scan tool in order to clear the MIL/DTC. |
Diagnostic Aids
Important:
• Remove any debris from the PCM\TAC module connector surfaces before
servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets
when diagnosing/replacing the modules. Ensure that the gaskets are installed
correctly. The gaskets prevent contaminate intrusion into the PCM\TAC
modules. • For any test that requires probing the PCM or a component
harness connector, use the Connector Test Adapter Kit J 35616
. Using this kit prevents damage
to the harness/component terminals. Refer to
Using Connector Test Adapters
in Wiring Systems.
For an intermittent condition, refer to Symptoms .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines whether the fault is present.
-
Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed.
-
If DTC 175 is also set, then both banks are operating rich. Inspect items that would cause both banks to operate rich.
-
Excessive fuel in the oil will cause DTCs P0172 and P0175 to set at the same time. Remove the PCV valve from the intake manifold and plug with a suitable stopper. Also disconnect the fresh air pipe from the rocker cover and plug with a suitable stopper. If the long term and short term fuel trim values increase, this indicates there is fuel in the oil.
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||
|
Important: If any DTCs are set, except P0172 and P0175, refer to those DTCs before proceeding with this diagnostic.
Is the LT FT greater than the specified value indicated (greater than equals -12, -11 etc.)? | -13% LT | |||||||||||||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | ||||||||||||
Is DTC P0175 also set? | -- | |||||||||||||
Visually/physically inspect the following items:
Was a problem found in any of the above areas? | -- | Go to Fuel System Diagnosis | ||||||||||||
6 |
Important: When the fuel system testing is finished, return to this table. Inspect the Bank 1 injectors for leaking, refer to Fuel System Diagnosis . Did any injectors require replacement? | -- | ||||||||||||
7 | Repair or replace any faulty items found. Is the action complete? | -- | -- | |||||||||||
8 | Replace the faulty HO2S. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |||||||||||
9 |
Does the scan tool indicate that this test ran and passed? | -- | ||||||||||||
10 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
