For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC P2178 : Fuel Trim System Rich at Cruise or Accel Bank 1
DTC P2180 : Fuel Trim System Rich at Cruise or Accel Bank 2
DTC P2188 : Fuel Trim System Rich at Idle Bank 1
DTC P2190 : Fuel Trim System Rich at Idle Bank 2

### 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 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.

### Conditions for Running the DTC

#### P2178 or P2180

• | Before the ECM can report DTC P2178 or P2180, failed, DTCs P0008, P0009, P0010, P0011, P0013, P0014, P0016, P0017, P0018, P0019, P0020, P0021, P0023, P0024, P0101, P0121, P0122, P0123, P0133, P0153, P0201, P0202, P0203, P0204, P0205, P0206, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0335, P0336, P0338, P0443, P0458, P0459, P0461, P0462, P0463, P2068 P2088, P2089, P2090, P2091, P2092, P2093, P2094, and P2095 must run and pass.

• | The engine speed is between 1,200-3,400 RPM.

• | The mass air flow (MAF) is less than 83 grams/second.

• | The throttle angle is less than 100 percent.

• | The engine load is between 17-45 percent.

• | The fuel system is in closed loop.

• | The engine is not in decel fuel cut-off (DEFCO).

• | The long term fuel trim is active.

• | The engine coolant temperature (ECT) is greater than 60°C (140°F).

• | The intake air temperature (IAT) is less than 60°C (140°F).

• | The evaporative emission (EVAP) canister purge solenoid valve is not enabled.

• | The fuel level is greater than 12 percent.

• | The amount of air flow into the engine is greater than 7,000 grams.

• | DTCs P2178, P2180 run continuously once the above conditions are met for at least 300 seconds.

#### P2188 or P2190

• | Before the ECM can report DTC P2188 or P2190, failed, DTCs P0008, P0009, P0010, P0011, P0013, P0014, P0016, P0017, P0018, P0019, P0020, P0021, P0023, P0024, P0101, P0121, P0122, P0123, P0133, P0153, P0201, P0202, P0203, P0204, P0205, P0206, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0335, P0336, P0338, P0443, P0458, P0459, P0461, P0462, P0463, P2068 P2088, P2089, P2090, P2091, P2092, P2093, P2094, and P2095 must run and pass.

• | The engine speed is between 519-1,001 RPM.

• | The engine load is between 7-25 percent.

• | The MAF is between 1-7 grams per second.

• | The fuel system is in Closed Loop.

• | The engine is not in decel fuel cut-off (DEFCO).

• | The long term fuel trim is active.

• | The engine coolant temperature (ECT) is greater than 60°C (140°F).

• | The intake air temperature (IAT) is less than 60°C (140°F).

• | The evaporative emission (EVAP) canister purge solenoid valve is not enabled.

• | The fuel level is greater than 12 percent.

• | The amount of air flow into the engine is greater than 7,000 grams.

• | DTC P2188 and P2190 run continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P2178 or P2180

The Total Fuel Trim Avg. is less than -22 percent. The condition exists for 4 seconds or for a cumulative of 50 seconds.

#### P2188 or P2190

The Total Fuel Trim Avg. is less than -40 percent. The LT FT Idle/Decel is less than -7 percent. The condition exists for 4 seconds or for a cumulative of 50 seconds.

### Action Taken When the DTC Sets

DTCs P2178, P2180, P2188, and P2190 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P2178, P2180, P2188, and P2190 are Type B DTCs.

### Diagnostic Aids

A fuel system delivery condition causes this DTC to set. Thoroughly inspect all items that cause a rich condition. Refer to Fuel System Diagnosis.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, observe the scan tool DTC information. Verify that there are no other DTCs set.

⇒ | If there are other DTCs set besides DTC P2178, P2180, P2188, or P2190, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

2. Observe the scan tool barometric pressure (BARO) sensor pressure parameter and compare the reading on the scan tool to the barometric pressure table. Refer to Altitude Versus Barometric Pressure.

⇒ | If the BARO sensor pressure is not within the range specified for your altitude, refer to DTC P2227, P2228, or P2229.

3. Engine idling at normal operating temperature, observe the scan tool Total Fuel Trim Avg. parameter. The Total Fuel Trim Avg. should be between -22 to +23 percent.
4. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

### Circuit/System Testing

1. Observe the scan tool LT FT Bn 1 and Bn 2 Cruise/Accel or Idle/Decel parameters, in order to determine whether the rich condition is effecting only one bank of the engine, or is common to both banks of the engine.

⇒ | If the rich condition is common to both banks, inspect for the following conditions:

• | A mass air flow (MAF) sensor signal that is skewed. If the Short Term FT parameters for both banks changes greater than 20 percent when the MAF sensor is disconnected, refer to DTC P0101.

• | A collapsed air intake duct

• | A restricted air filter element--Refer to Air Cleaner Element Replacement.

• | The MAF sensor for foreign objects--Refer to Mass Airflow Sensor Replacement.

• | Excessive fuel in the crankcase--Change the oil as necessary.

• | Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis.

• | The engine control module grounds for being clean, tight, and in the correct locations.

• | An engine mechanical condition--Refer to Symptoms - Engine Mechanical.

⇒ | If the rich condition is common to only one bank of the engine, inspect for the following conditions:

• | Rich injectors--Refer to Fuel Injector Solenoid Coil Test.

• | Restricted exhaust system--Refer to Symptoms - Engine Exhaust.

• | An engine mechanical condition--Refer to Symptoms - Engine Mechanical.

2. If all conditions test normal, refer to Diagnostic Aids.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fuel Injection Fuel Rail Assembly Replacement

• | Fuel Injection Fuel Rail Assembly Replacement

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2