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 Descriptor

DTC P0172 00: Fuel Trim System Rich
DTC P2097 00: Fuel Trim System Rich

### 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 loop 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 ECM adds heated oxygen sensor (HO2S) inputs and level of purge to calculate the short and long term fuel trim adjustments. If the heated oxygen sensor (HO2S) indicates a lean condition, the fuel trim values will be above 0%. If the heated oxygen sensor (HO2S) indicates a rich condition, the fuel trim values will be below 0%. The short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. The long term fuel trim makes rough adjustments in order to maintain an air/fuel ratio of 14.7:1.

The heating elements inside each heated oxygen sensor (HO2S) heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter closed loop earlier and the control module to calculate the air-to-fuel ratio sooner.

The HO2S utilizes the following circuits:

• | A signal circuit

• | A low reference circuit

• | An ignition voltage circuit

• | A heater control circuit

### Conditions for Running the DTC

#### P0172 00

• | DTCs P0030 00, P0031 00, P0032 00, P0111 00, P0112 00, P0113 00, P0114 00, P0117 00, P0118 00, P0119 00, P0122 00, P0123 00, P0130 00, P0131 00, P0132 00, P0133 00, P0134 00, P0135 00, P0201 00, P0202 00, P0203 00, P0204 00, P0222 00, P0223 00, P0261 00, P0262 00, P0264 00, P0265 00, P0267 00, P0268 00, P0270 00, P0271 00, P0301 00, P0302 00, P0303 00, P0304 00, P0335 00, P0336 00, P0340 00, P0341 00, P0365 00, P0366 00, P0443 00, P0458 00, P0459 00, P0496 00, P2227 00, P2228 00, P2229 00, P2297 00, P2A00 00 are not set.

• | The loop status parameter indicates closed.

• | The engine coolant temperature (ECT) is between -38°C and +150°C (-36.4°F and +302°F).

• | The intake air temperature (IAT) is between -38°C and +150°C (-36.4°F and +302°F).

• | The manifold absolute pressure (MAP) is between 5-255 kPa (0.73-37 PSI).

• | The engine speed is between 400-6000 RPM.

• | The barometric pressure (BARO) is more than 70 kPa (10 PSI).

• | DTCs P0172 00 and P2097 00 run continuously when the above conditions have been met.

#### P2097 00

• | DTCs P000A 00, P000B 00, P0010 00, P0011 00, P0013 00, P0016 00, P0017 00, P0030 00, P0031 00, P0032 00, P0117 00, P0118 00, P0119 00, P0121 00, P0122 00, P0123 00, P0131 00, P0132 00, P0133 00, P0137 00, P0138 00, P0139 00, P0140 00, P0141 00, P0171 00, P0172 00, P0201 00, P0202 00, P0203 00, P0204 00, P0221 00, P0222 00, P0223 00, P0261 00, P0262 00, P0264 00, P0265 00, P0267 00, P0268 00, P0270 00, P0271 00, P0300 00, P0301 00, P0302 00, P0303 00, P0304 00, P0313 00, P0335 00, P0336 00, P0340 00, P0341 00, P0365 00, P0366 00, P0420 00, P0443 00, P0458 00, P0459 00, P2088 00, P2089 00, P2090 00, P2091 00, P2100 00, P2101 00, P2176 00, P2270 00, P2271 00, P2297 00, P2300 00, P2301 00, P2303 00, P2304 00, P2306 00, P2307 00, P2309 00, P2310 00, P2A00 00, P2A01 00 are not set.

• | The ignition is ON.

• | The evaporative emission (EVAP) system is not purging.

• | The post catalyst fuel trim is enabled.

• | This DTC P2097 00 runs continuously when the above conditions have been met.

### Conditions for Setting the DTC

#### P0172 00

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

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

#### P2097 00

The long term fuel trim has reached its limit while the heated oxygen sensor (HO2S) voltage is still trying to move the adjustment further in the same direction.

### Action Taken when the DTC Sets

DTCs P0172 00 and P2097 00 are Type B DTC.

### Conditions for Clearing the DTC

DTCs P0172 00 and P2097 00 are Type B DTC.

### Diagnostic Aids

• | On vehicles equipped with a vacuum brake booster, rapid brake pedal cycling may imitate a vacuum leak.

• | A failed HO2S will not cause DTC P2097 00 to set without the occurrence of circuit related HO2S DTCs. Do not replace an HO2S to address this DTC.

• | An exhaust system leak that may not be audible can set these DTC's.

### 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

Note: 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. Verify that other DTCs are not set.

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

2. Allow the engine to reach operating temperature. With the engine running, observe the HO2S Sensor 1 parameter with a scan tool. The HO2S 1 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 LINK or DTC P0137-P0140, P2270, P2271, or P2A01.

Note: The EVAP purge enablement may cause the fuel trim to be momentarily outside the normal range.

3. The normal short term fuel trim parameter should be between +10% and -10%, with near 0% the optimum, with the engine running at operating temperature.
4. The long term fuel trim parameter should be between +10% and -10%, with near 0% the optimum, with the engine running at operating temperature.
5. Operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.

### Circuit/System Testing

Note: Allow the engine to reach operating temperature. With the engine running, observe the long term fuel trim parameter with a scan tool. The value should be less than approximately 18% with the engine running at operating temperature.

⇒ | If the value is not less than -25%, inspect for the following:

• | With the ignition ON and the engine OFF, observe the HO2S Sensor 1 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 LINK (DTC P0107 00 or P0108 00).

• | With the engine idling and the transmission in the park or neutral position, observe the MAP Sensor parameter. The MAP Sensor parameter should be between 19-42 kPa (2.8-6.1 PSI).

⇒ | If the MAP sensor parameter is not between 19-42 kPa (2.8-6.1 PSI), refer to LINK (DTC P0107 00 or P0108 00).

• | 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 LINK (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 B52A Heated Oxygen Sensor (HO2S) sensor 1 signal circuit open, shorted to ground, or shorted to the low reference circuit

• | The B52A Heated Oxygen Sensor (HO2S) sensor 1 low signal circuit for an open circuit or high resistance

### Repair Instructions

• | Air Cleaner Assembly Replacement.

• | Air Cleaner Element Replacement.

• | LINK (Evaporative Emission Canister Purge Solenoid Valve Replacement).

• | Evaporative Emission Canister Replacement.

• | LINK (Evaporative Emission Canister Vent Solenoid Valve Replacement).

• | LINK (Fuel Hose/Pipes Replacement - Chassis).

• | Fuel Injector Replacement.

• | Fuel Sender Assembly Replacement.

• | Fuel System Cleaning.

• | Heated Oxygen Sensor Replacement - Sensor 1

• | Manifold Absolute Pressure Sensor Replacement.

• | Throttle Body Assembly Replacement.

### Repair Verification

Note: 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.

Note: 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 s.
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 00. Refer to DTC P0420.