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 P2177: Fuel Trim System Lean at Cruise or Accel Bank 1
DTC P2179: Fuel Trim System Lean at Cruise or Accel Bank 2
DTC P2187 : Fuel Trim System Lean at Idle Bank 1
DTC P2189: Fuel Trim System Lean 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 checks 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

#### P2177 or P2179

• | Before the ECM can report DTC P2177 or P2179 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, P2068 P2088, P2089, P2090, P2091, P2092, P2093, P2094, and P2095 must run and pass.

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

• | The engine speed is between 1,200-3,340 RPM.

• | The throttle angle is less than 100 percent.

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

• | The Closed Loop fuel control is enabled.

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

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

• | DTC P2177 and P2179 run continuously when the above conditions are met for approximately 300 seconds, after Closed Loop fuel control is enabled.

#### P2187 or P2189

• | Before the ECM can report DTC P2187 or P2189 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, P2068 P2088, P2089, P2090, P2091, P2092, P2093, P2094, and P2095 must run and pass.

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

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

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

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

• | The engine is not in DFCO.

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

• | DTCs P2187 and P2189 run continuously when the above conditions are met for approximately 300 seconds, after Closed Loop fuel control is enabled.

### Conditions for Setting the DTC

#### P2177 or P2179

The Long Term Fuel Trim Cruise/Accel is greater than 23 percent for 4 seconds, or for a cumulative time of 30 seconds.

#### P2187 or P2189

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

### Action Taken When the DTC Sets

DTCs P2177, P2179, P2187 and P2189 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P2177, P2179, P2187 and P2189 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 scan tool LT FT Bn 1 and Bn 2 parameters while driving the vehicle can determine whether the lean condition is affecting 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 lean condition. Refer to Fuel System Diagnosis.

• | Any un-metered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum leaks.

• | A mass air flow (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.

• | Inspect the air filter for being the correct one for this application. Make sure that the engine oil fill cap is in place and that it is tight. Verify that the engine oil dip stick is fully seated.

### 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 P2177, P2179, P2187, or P2189 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 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 at normal operating temperature, observe the scan tool Long Term Fuel Trim parameters. The LT FT Cruise/Accel parameters should be less than 24 percent. The LT FT Idle/Decel parameters should be less than 7 percent.

⇒ | If a parameter is not within the specified range, inspect for the following conditions:

• | The heated oxygen sensor (HO2S) is installed securely and the electrical connector is not contacting the exhaust system.

• | Missing, restricted, or leaking exhaust components--Refer to Symptoms - Engine Exhaust.

• | The air intake system after the MAF sensor for vacuum leaks

• | A 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.

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

• | Splits, kinks, or improper connections at the vacuum hoses--Refer to Emission Hose Routing Diagram.

• | The fuel system is operating lean. Refer to Fuel System Diagnosis.

• | Vacuum leaks at the intake manifold or throttle body

• | Leaking crankcase ventilation system

• | The ECM grounds for being clean, tight, and in the correct locations

• | A high engine oil level condition--A high engine oil level causes oil residue to form on the MAF sensor, causing a lean indication. The MAF sensor does not need to be replaced.

• | Vacuum leaks that only affect one bank of the engine--For example, the intake manifold, the injector O-rings.

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

• | 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.