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

### Circuit/System 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 Loop and Closed Loop (CL). During Open Loop, the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During CL, the ECM adds HO2S inputs to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0 percent. If the HO2S indicates a rich condition, the FT values will be below 0 percent. The short term FT values change rapidly in response to the HO2S voltage signals. The long term FT makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1.

If the ECM detects an excessively lean condition at cruise or during acceleration, DTC P2177 sets.

If the ECM detects an excessively lean condition at idle, DTC P2187 sets.

### Conditions for Running the DTC

#### P2177

• | DTCs P0010, P0011, P0013, P0014, P0030, P0031, P0032, P0053, P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0125, P0130, P0131, P0132, P0133, P0135, P0335, P0336, P0338, P0443, P0455, P0458, P0459, P0496, P167A, P2088, P2089, P2090, P2091, P2096, P2097, P2176, P2195, P2196, P2231, P2237, P2243, P2251, P2297, P2626 are not set.

• | The engine is running.

• | The engine is in Closed Loop for more than 1 minute.

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

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

• | The commanded lambda is between 0.83-1.2.

• | The deceleration fuel cut-off (DFCO) is not active.

• | The fuel level is more than 10 percent.

• | The mass air flow is between 7.5-83.3 g/s.

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

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

• | The throttle angle is equal to or less than 99.6 percent.

• | DTC P2177 runs continuously when the above conditions have been met for 1 second.

#### P2187

• | DTCs P0010, P0011, P0013, P0014, P0030, P0031, P0032, P0053, P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0125, P0130, P0131, P0132, P0133, P0135, P0335, P0336, P0338, P0443, P0455, P0458, P0459, P0496, P167A, P2088, P2089, P2090, P2091, P2096, P2097, P2176, P2195, P2196, P2231, P2237, P2243, P2251, P2297, P2626 are not set.

• | The engine is running.

• | The engine is in Closed Loop for more than 1 minute.

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

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

• | The commanded lambda is between 0.83-1.2.

• | The deceleration fuel cut-off (DFCO) is not active.

• | The fuel level is more than 10 percent.

• | The mass air flow is equal to or between 1.4- 6.7 g/s.

• | The engine load is equal to or between 7.5-24.8 percent.

• | DTC P2187 runs continuously when the above conditions have been met for 1 second.

### Conditions for Setting the DTC

• | The long term FT weighted average value is more than a calibrated value at idle, cruise or during acceleration.

• | DTC P2177 or DTC P2187 sets when the above condition is met for 4 seconds continuously, or for 50 seconds cumulatively.

### 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.

### Reference Information

#### 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

#### Emission System Information Reference

• | Evaporative Emissions Hose Routing Diagram

• | Crankcase Ventilation System Inspection/Diagnosis

#### Engine Mechanical Information Reference

• | Symptoms - Engine Mechanical

• | Symptoms - Engine Exhaust

#### Fuel System Information Reference

• | Fuel System Diagnosis

• | Alcohol/Contaminants-in-Fuel Diagnosis

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Verification

Important: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system (TCS) indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions such as harsh shifts and illumination of the ABS/TCS indicators.

1. If any other DTCs are set, perform those diagnostics first.
2. Operate the vehicle within the parameters described in Conditions for Running and Conditions for Setting. The DTC should not set this ignition.

⇒ | If the DTC sets this ignition, proceed with Circuit/System Testing.

### Circuit/System Testing

Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

Allow the engine to reach operating temperature. With the engine idling, observe the Long Term FT parameter with a scan tool. The value should be less than approximately 20 percent with the engine running at operating temperature.

⇒ | If the value is more than 20 percent, inspect for the following:

• | With the ignition ON and the engine OFF, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .

⇒ | If the MAP sensor does not indicate the correct barometric pressure, refer to DTC P0106, P0107, or P0108 .

• | With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be between 2-6 g/s at idle.

⇒ | If the MAF sensor parameter is not between 2-6 g/s at idle, refer to DTC P0100, P0101, P0102, or P0103 .

• | Vacuum hoses for splits, kinks, and improper connections

• | Insufficient fuel in the tank

• | Low fuel pressure

• | Fuel contamination

• | Malfunctioning fuel injectors

• | Missing, loose, or leaking exhaust components from the HO2S forward

• | Vacuum leaks at the intake manifold, the throttle body, and the injectors

• | The air induction system and the air intake ducts for leaks or for a missing air filter element

• | A cracked EVAP canister

• | Evaporative pipes obstructed or leaking

• | The crankcase ventilation system for leaks

• | The HO2S for improper installation and for electrical wires or connectors that may have suffered corrosion, water intrusion, or contacted the exhaust system

• | Incorrect terminal tension at electrical connectors

• | Loose, corroded, or mislocated electrical ground connections

• | The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit

• | Malfunctioning engine components

### Repair Instructions

• | Air Cleaner Assembly Replacement

• | Air Cleaner Element Replacement

• | Air Cleaner Outlet Duct Replacement

• | Direct Fuel Injector Replacement

• | Evaporative Emission Canister Replacement

• | Evaporative Emission Canister Purge Solenoid Valve Replacement

• | Evaporative Emission Canister Vent Solenoid Valve Replacement

• | Evaporative Emission Hoses/Pipes Replacement - Canister/Fuel Tank

• | Evaporative Emission Hoses/Pipes Replacement - Chassis/Canister

• | Evaporative Emission Hoses/Pipes Replacement - Engine/Chassis

• | Fuel Feed Pipe Replacement

• | Fuel Hose/Pipes Replacement - Chassis

• | Fuel Pump Fuel Feed Hose Replacement

• | Fuel Pump Module Replacement

• | Fuel System Cleaning

• | Fuel Tank Draining

• | Heated Oxygen Sensor 1 Replacement

• | Manifold Absolute Pressure Sensor Replacement

• | Mass Airflow Sensor Replacement

• | Throttle Body Assembly Replacement

### Repair Verification

Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the long term fuel trim.

1. Install any components or connectors that have been removed or replaced during diagnosis.
2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced.
3. Turn ON the ignition, with the engine OFF.

Important: DO NOT clear codes with the engine running. The codes may reset in the same ignition cycle.

4. Clear the DTCs.
5. Turn OFF the ignition for 60 seconds.
6. Start the engine.
7. Duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets, or another DTC is present, refer to the Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.
8. To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420. Refer to DTC P0420 .