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 Acceleration
DTC P2187 : Fuel Trim System Lean at Idle

### 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 delivery adjustments. If the HO2S indicate a lean condition, fuel trim values will be above 0 percent. If the HO2S 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

• | Before the ECM can report DTC P2177 failed, DTCs P0008, P0009, P0010, P0011, P0013, P0014, P0016, P0017, P0018, P0019, P0020, P0021, P0023, P0024, P0101, P0121, P0122, P0123, P0133, 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 is between 7-83 grams/second.

• | The throttle angle is less than 100 percent.

• | The engine load is between 17-55 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 61°C (142°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 P2177 runs continuously once the above conditions are met for at least 300 seconds.

#### P2187

• | Before the ECM can report DTC P2187 failed, DTCs P0008, P0009, P0010, P0011, P0013, P0014, P0016, P0017, P0018, P0019, P0020, P0021, P0023, P0024, P0101, P0121, P0122, P0123, P0133, 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 480-1,001 RPM.

• | The engine load is between 7-32 percent.

• | The MAF is between 1-8 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 61°C (142°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 P2187 and P2189 run continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P2177

The Total Fuel Trim Avg. is greater than 23 percent for 4 seconds or for a cumulative of 30 seconds.

#### P2187

The Total Fuel Trim Avg. is greater than 40 percent, or the LT FT Idle/Decel is greater than 6 percent. Either condition exists for 4 seconds or for a cumulative of 30 seconds.

### Action Taken When the DTC Sets

DTCs P2177 and P2187 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P2177 and P2187 are Type B DTCs.

### Diagnostic Aids

• | 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 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 or P2187 should not be set.

⇒ | If there are other DTCs set besides DTC P2177 or P2187 refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnosis the applicable DTC.

2. Ignition ON, observe the BARO pressure parameter and compare the reading on the scan tool to the barometric pressure table. Refer to Altitude Versus Barometric Pressure.

⇒ | If the BARO 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 Average Total Fuel Trim parameter with a scan tool. The Average Total Fuel Trim should be between -22 to +23 percent.

⇒ | If not within the specified range, verify none of the following conditions exist:

• | A mass air flow sensor signal that is skewed--If the Short Term Fuel Trim parameter changes greater than 20 percent when the MAF sensor is disconnected, refer to DTC P0101.

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

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

• | Splits, kinks, or improper connections at the vacuum hoses.

• | 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 engine control module 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 mass air flow 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.

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

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

• | 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.