Circuit Description
To provide the best possible combination of driveability, fuel economy and emission control, a Closed Loop air/fuel metering system is used. While in Closed Loop, the PCM monitors the heated oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery will be indicated by the Long and Short Term Fuel Trim values. Short Term Fuel Trim values change rapidly in response to the HO2S signal voltages. These changes fine tune engine fueling. Long Term Fuel Trim values change in response to trends in Short Term Fuel Trim. Long Term Fuel Trim makes coarse adjustments to fueling in order to re-center and restore control to Short Term Fuel Trim. Short and Long Term Fuel Trim can be monitored with a scan tool. Ideal fuel trim values are around 0%. A positive Fuel Trim value indicates that the PCM is adding fuel to compensate for a lean condition. A negative Fuel Trim value indicates that the PCM is reducing the amount of fuel to compensate for a rich condition. If an excessively Rich or Lean condition is detected, the PCM will set a DTC. The long term fuel trim diagnostic parameter is an average of several of the long term speed load learn cells which are selected based on speed and load.
Conditions for Setting the DTC
| • | DTCs P0100, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0134, P0135, P0151, P0152, P0154, P0155, P0200, P0300, P0372, P0441, P0443, P0500, P0601, P1133, P1153, P1351, P1361, P1371, P1415, P1416, P1441 not set. |
| • | Engine Coolant Temperature between 60°C (120°F) and 115°C (239°F). |
| • | Fuel system operating in Closed Loop. |
| • | Fuel trim enabled. |
| • | Barometric Pressure greater than 70 kPa. |
| • | Mass Air Flow between 5 grams per second and 100 grams per second. |
| • | Manifold Absolute Pressure between 20 kPa and 90 kPa. |
| • | Intake Air Temperature between -30°C (-22°F) and 150°C (302°F). |
| • | EVAP Canister purge not enabled or EVAP Canister purge duty cycle greater than 75%. |
| • | Engine speed between 500 RPM and 4000 RPM. |
| • | TP Sensor angle less than 75%. |
| • | Vehicle speed less than 121 km/h (75 mph). |
| • | The PCM detects the average Long Term Fuel Trim cell values are below a predetermined threshold. |
| • | All above conditions met for approximately 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails, if the diagnostic fails under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed. |
| • | The first time the diagnostic fails, the PCM will record operating conditions in Failure Records. |
| • | The second consecutive drive trip that this diagnostic fails [under the same conditions (load, RPM, temperature, etc.) as the previous ignition cycle that the test ran and failed], this information will be stored in Freeze Frame. Any data previously stored in Freeze Frame will be copied into Failure Records and Freeze Frame will be overwritten by this DTC. The only exception to this is if a Misfire DTC was already recorded in Freeze Frame. In this case, the Misfire data stays in Freeze Frame and the Fuel Trim data will be updated in Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF after three consecutive drive trips that 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 three drive trips. Review Freeze Frame/Failure Records for the last failure conditions. |
| • | A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | A last test failed (Current DTC) will clear when the diagnostic runs and does not fail. |
| • | PCM battery voltage is interrupted. |
| • | Using a Scan tool. |
Diagnostic Aids
For intermittents, refer to Symptoms .
Test Description
Number(s) below refer to step numbers on the diagnostic table.
-
Determines whether the fault is present.
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Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that were noted. This will isolate when the DTC failed.
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If DTC 172 is also set, then both banks are operating rich. Inspect items that would cause both banks to operate rich.
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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 and short trim values increase, indicates there is fuel in the oil.
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||||
|
Important: If any DTCs are set (Except P0172 and P0175) refer to those DTCs before proceeding with this diagnostic.
Is LT FT and the ST FT greater than the specified values indicated? | -14% LT -10% ST | |||||||||||||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | ||||||||||||
Is DTC P0172 also set? | -- | |||||||||||||
5 | 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 check is finished, return to this table. Inspect injectors for leaking (Bank 2), refer to Fuel System Diagnosis . Was any injector(s) leaking? | -- | ||||||||||||
7 | Repair or replace any faulty items found. Is the action complete? | -- | -- | |||||||||||
8 | Replace 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 | Using the scan tool, select Capture Info, Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
