P2178

DTC P2178

Circuit Description

The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop, the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During Closed Loop, the HO2S inputs are added and used by the ECM to calculate short and long term fuel trim fuel delivery adjustments. If the HO2S indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensor (O2S) indicate a rich condition, fuel trim values will be below 0 percent. Short term fuel trim values change rapidly in response to the HO2S signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. If the ECM detects an excessively rich condition, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P2178 Fuel Trim System Rich at Cruise or Accel

Conditions for Running the DTC

* Before the ECM can report DTC P2178 failed, DTCs P0030, P0031, P0032, P0053, P0101, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0135, P0221, P0222, P0223, P0335, P0336, P0338, P0443, P0458, P0459, P167A, P2096, P2097, P2196, P2231, P2237, P2243, P2251, and P2626 must run and pass.
* DTCs P0010, P0011, P0013, P0014, P0020, P0021, P0023, P0024, P0455, P0496, P0117, P0118, P0125, P2088, P2089, P2090, P2091, P2092, P2093, P2094, P2095, and P2176 are not set.
* The fuel system is in closed loop.
* The long fuel trim is active.
* The engine coolant temperature (ECT) is more than 60±C (140°F).
* The evaporative emission (EVAP) canister purge solenoid valve is not enabled.
* The intake air temperature (IAT) is less than 66°C (151°F).
* The fuel level is more than 10 percent.
* DTC P2178 runs continuously once the above conditions are met for at least 300 seconds.

Conditions for Setting the DTC

* The Total Fuel Trim Avg. is less than -22 percent.
* The condition exists for 4 seconds.

Action Taken When the DTC Sets

* The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
* The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

* The control module turns OFF the malfunction indicator lamp (MIL) at the beginning of the fourth ignition cycle, after 3 ignition cycles that the diagnostic runs and does not fail.
* A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
* A history DTC and related Freeze Frame data clears after 40 warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
* Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

* A fuel delivery condition causes this DTC to set. Thoroughly inspect all items that cause a rich condition.
* For an intermittent condition, Refer to Intermittent Conditions. Intermittent Conditions

Test Description

Step 1 - Step 5:

Step 6 - Step 7:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines whether the fault is present.
4. Disconnecting the MAF sensor determines if the MAF sensor signal is skewed. If the Short Term FT parameter changes more than the specified value, there is a condition with the MAF sensor. A MAF sensor condition can cause this DTC without setting a MAF DTC. If there is a MAF sensor condition, the MAF sensor parameters will appear to be within range.