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 procedure.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC P0172: Fuel Trim System Rich
DTC P2097: Post Catalyst Fuel Trim System High Limit

### 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 and level of purge to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicates a lean condition, the FT 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.

### Conditions for Running the DTC

#### P0172

• | DTCs P0030, P0031, P0032, P0068, P0071, P0072, P0073, P0074, P009A, P0101, P0102, P0103, P0111, P0112, P0113, P0114, P0116, P0117, P0118, P0119, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0201, P0202, P0203, P0204, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0301, P0302, P0303, P0304, P0335, P0336, P0340, P0341, P0365, P0366, P0443, P0458, P0459, P0496, P1101, P2227, P2228, P2229, P2297, P2A00 are not set.

• | The engine is in CL status.

• | The engine coolant temperature (ECT) is warmer than 65.3°C (149.5°F).

• | The intake air temperature (IAT) is warmer than -9.8°C (+14.4°F).

• | The engine speed is greater than 608 RPM.

• | The mass air flow (MAF) is within a calibrated range.

• | The barometric pressure (BARO) is more than 70 kPa.

#### P2097

• | DTCs P000A, P000B, P0010, P0011, P0013, P0014, P0016, P0017, P0030, P0031, P0032, P0036, P0037, P0038, P0068, P0101, P0102, P0103, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0137, P0138, P0139, P0140, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0300, P0301, P0302, P0303, P0304, P0313, P0335, P0336, P0340, P0341, P0365, P0366, P0420, P0443, P0458, P0459, P1101, P2088, P2089, P2090, P2091, P2100, P2101, P2176, P2270, P2271, P2297, P2300, P2301, P2303, P2304, P2306, P2307, P2309, P2310, P2A00, P2A01 are not set.

• | The ignition is ON.

• | The EVAP system is not purging.

• | The post catalyst fuel trim is enabled.

• | These DTCs run continuously when the above conditions have been met.

### Conditions for Setting the DTC

#### P0172

• | The long term FT weighted average value is more or less than a calibrated value.

• | The above condition is present for approximately 3 minutes after the conditions for running the DTC have been met.

#### P2097

The long term FT has reached its limit while the HO2S voltage is still trying to move the adjustment further in the same direction.

### Action Taken When the DTC Sets

DTCs P0172 and P2097 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0172 and P2097 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

#### Scan Tool Reference

Control Module References for scan tool information

### 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.

• | Verify that other DTCs are not set.

⇒ | If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

• | Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S value should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.

⇒ | If the value does not vary from approximately 40 mV to approximately 900 mV, refer to DTC P0130-P0134, P2297, or P2A00 or DTC P0137-P0140, P2270, P2271, or P2A01.

| Important: EVAP purge enablement may cause the FT to be momentarily outside the normal range.

• | The normal B1 Short Term Fuel Trim parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.

• | The B1 Long Term Fuel Trim parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.

### Circuit/System Testing

Allow the engine to reach operating temperature. With the engine running, observe the B1 Long Term Fuel Trim parameter with a scan tool. The value should be more than approximately -25 percent with the engine running at operating temperature.

⇒ | If the value is not more than -25 percent, inspect for the following:

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

⇒ | If the BARO sensor does not indicate the correct barometric pressure, refer to DTC P2227, P2228, or P2229.

• | 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 P0101 or P1101 or DTC P0102 or P0103.

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

• | The air intake duct for being collapsed or restricted

• | The air filter for being dirty or restricted

• | Objects blocking the throttle body

• | Excessive fuel in the crankcase due to leaking fuel injectors

• | The evaporative emissions control system for improper operation

• | Excessive fuel pressure--Refer to Fuel System Diagnosis.

• | Malfunctioning fuel injectors--Refer to Fuel Injector Diagnosis.

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

• | The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system

• | The HO2S signal circuit shorted to voltage

### Repair Instructions

• | Air Cleaner Assembly Replacement

• | Air Cleaner Inlet Duct Replacement

• | Evaporative Emission Canister Replacement

• | Evaporative Emission Canister Purge Solenoid Valve Replacement

• | Evaporative Emission Canister Vent Solenoid Valve Replacement

• | Fuel Injector Replacement

• | Fuel Tank Fuel Pump Module Replacement

• | Heated Oxygen Sensor Replacement - Sensor 1

• | Barometric 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.