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
DTC P2187: Fuel Trim System Lean at Idle
DTC P2191: Fuel Trim System Lean at Higher Load

### 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

#### P2177

• | The engine load is between 27-85 percent.

• | The fuel system is in closed loop.

• | The engine coolant temperature (ECT) is greater than 70°C (158°F).

• | The intake air temperature (IAT) is less than 80°C (176°F).

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

• | The amount of air flow into the engine is between 50-350 kg/h.

• | The above conditions are met for greater than 30 seconds.

#### P2187

• | The engine speed is less than 1000 RPM.

• | The fuel system is in closed loop.

• | The engine coolant temperature (ECT) is greater than 70°C (158°F).

• | The intake air temperature (IAT) is less than 80°C (176°F).

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

• | The amount of air flow into the engine is less than 23 kg/h.

• | The above conditions are met for greater than 20 seconds.

#### P2191

• | The engine speed is greater than 1200 RPM.

• | The engine load is between 10-20 percent.

• | The fuel system is in closed loop.

• | The engine coolant temperature (ECT) is greater than 70°C (158°F).

• | The intake air temperature (IAT) is less than 80°C (176°F).

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

• | The above conditions are met for greater than 20 seconds.

### Conditions for Setting the DTC

#### P2177

The ECM detects that the Total Fuel Trim Avg. is greater than a predetermined amount during cruise or accel.

#### P2187

The ECM detects that the Total Fuel Trim Avg. is greater than a predetermined amount during idle.

#### P2191

The ECM detects that the Total Fuel Trim Avg. is greater than a predetermined amount during a higher load.

### Action Taken When the DTC Sets

DTCs P2177, P2187, and P2191 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P2177, P2187, and P2191 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 unmetered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum leaks.

• | Inspect the PCV valve for being the correct one for this application. 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. If there are other DTCs set besides DTC P2177, P2187, or P2191, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
2. Ignition ON, observe the scan tool barometric pressure (BARO) sensor pressure parameter and compare the reading to the barometric pressure table. Refer to Altitude Versus Barometric Pressure .
3. Engine at normal operating temperature, observe the scan tool Total Fuel Trim Avg. parameter. The reading should be between -22 to +23 percent.

### Circuit/System Testing

1. Verify none of the following conditions exist:

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

• | 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

• | 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 .

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor 1 Replacement

• | Heated Oxygen Sensor 2 Replacement

• | Control Module References for engine control module replacement, setup, and programming