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 fuel trim control system monitors the range of the air/fuel ratio in order to maintain the desired ratio for optimum emissions performance. The system performs tests during certain operating conditions to detect unmetered air or unmetered fuel. The fuel trim control system operation can be observed by monitoring the scan tool Short Term and Long Term Fuel Trim parameters.

### Conditions for Running the DTC

#### P2178 or P2180

• | Before the ECM can report DTC P2178 or P2180, failed, DTCs P000A, P000B, P000C, P000D, 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, P0464, P2068 P2088, P2089, P2090, P2091, P2092, P2093, P2094, P2095 P2146, P2149, P2152, P2155, P216A, and P216D must run and pass.

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

• | The engine load is between 13-40 percent.

• | The throttle angle is less than 100 percent.

• | The cold start fuel control is not active.

• | The closed loop fuel control is enabled.

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

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

• | The calculated amount of fuel metered into the engine is greater than 700 grams.

• | DTC P2178 and P2180 run continuously once the above conditions are met for approximately 300 seconds, after closed loop fuel control is enabled.

#### P2188 or P2190

• | Before the ECM can report DTC P2188 or P2190, failed, DTCs P000A, P000B, P000C, P000D, 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, P0464, P2068 P2088, P2089, P2090, P2091, P2092, P2093, P2094, P2095 P2146, P2149, P2152, P2155, P216A, and P216D must run and pass.

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

• | The engine load is between 0-24 percent.

• | The throttle angle is less than 100 percent.

• | The cold start fuel control is not active.

• | The closed loop fuel control is enabled.

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

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

• | The intake air temperature (IAT) is colder than 61°C (142°F).

• | The calculated amount of fuel metered into the engine is greater than 700 grams.

• | DTC P2188 and P2190 run continuously once the above conditions are met for approximately 300 seconds, after closed loop fuel control is enabled.

### Conditions for Setting the DTC

#### P2178 or P2180

The Long Term Fuel Trim Cruise/Accel is less than -22 percent for 4 seconds or for a cumulative of 30 seconds.

#### P2188 or P2190

The Long Term Fuel Trim Idle/Decel is less than -6 percent for 4 seconds or for a cumulative of 30 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

• | An HO2S will not cause this DTC to set without the occurrence of circuit related HO2S DTCs. Do not replace an HO2S to address this DTC.

• | Observing the LT FT Bn 1 and Bn 2 parameters, while driving the vehicle can determine whether the rich condition is effecting only one bank , or is common to both banks of the engine.

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

• | Review the Freeze Frame/Failure Records with a scan tool.

### 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. Observe the DTC information with a scan tool. DTC P2178, P2180, P2188, or P2190 should not be set.

⇒ | If any other DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnosis the applicable DTC.

2. Ignition ON, observe the 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 at normal operating temperature, observe the scan tool Long Term Fuel Trim parameters. The LT FT Cruise/Accel parameters should be greater than -23 %. The LT FT Idle/Decel parameters should be greater than -7 %.

⇒ | If not within the specified range, 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 % 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 with Intake Air Temperature Sensor Replacement.

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

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

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

• | 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.

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 you observed from the Freeze Frame/Failure Records data.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.