P0172

DTC P0172: Fuel Trim System Rich

System Description
To provide the best possible combination of driveability, fuel economy, and emission control, a Closed Loop air/fuel metering system is used. While in Closed Loop, the Engine Control Module (ECM) monitors the Heated Oxygen Sensor 1 (HO2S1) signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with the scan tool. Ideal fuel trim values are around 128 (0%). If the HO2S1 signal is indicating a lean condition, the ECM will add fuel resulting in fuel trim values above 128 (0% to 100%). If a rich condition is detected, the fuel trim values will be below 128 (0% to -100%), indicating that the ECM is reducing the amount of fuel delivered. If exhaust emissions reach an excessive level due to a lean or rich condition, a fuel trim Diagnostic Trouble Code (DTC) is set.

Conditions for Setting the DTC
- The average of short term fuel trim value is greater than 1.0601.
- No intrusive tests active.
- Throttle Position (TP) is less than 95%.
- Engine speed is between 700 and 6,000 rpm.
- Barometric Pressure (BARO) is greater than 72.0 kPa (10.4 psi).
- Coolant temperature is between 70 °C (158 °F) and 115 °C (239 °F).
- Manifold Absolute Pressure (MAP) is between 25 kPa (3.6 psi) and 99.7 kPa (14.5 psi).
- Intake Air Temperature (IAT) is between -40 °C (-40 °F) and 120 °C (248 °F).
- Airflow is between 1.5 and 45 g/sec.
- Vehicle speed is less than 140 km/h (87 mph).
- System is in Closed Loop.
- Adaptive index is ready.
- System voltage is greater than 11 V.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate after four consecutive ignitions in which the diagnostic runs with the fault active.
- The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- The MIL will turn OFF after four consecutive ignition cycles in which the diagnostic runs without a fault within the Freeze Frame conditions that the DTC failed.
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- The DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for more than 10 seconds.

Diagnostic Aids

NOTE: After repairs, use the scan tool Fuel Trim Reset function to reset the long-term fuel trim to 128 (0%).

Check for poor connection at the ECM. Inspect the harness connectors for the following conditions:
- Backed-out terminals
- Improper mating
- Broken locks
- Improperly formed
- Damaged terminals
- Poor terminal-to-wire connection

Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S1 display on the scan tool while moving the connectors and the wiring harness related to the engine harness. A change in the display will indicate the location of the fault.

If a DTC P042E is also set, check the 5 volt reference circuits for a short to voltage.

Check for a restricted exhaust system.

A shorted 5 volt reference circuit may cause a DTC P0172 to set. Check the 5 volt reference sensors for abnormal readings.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The On-Board Diagnostic (OBDII) System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred.
The information is then stored on the scan tool for later reference.
2. A clogged air cleaner filter element restricts the airflow coming into the engine. This step checks the condition of the air cleaner filter.
3. A leaky injector can cause a rich condition and set DTC P0172. Refer to Fuel Injector Balance Test.
4. A loose TP sensor may not set a TP sensor related DTC, but may cause the system to become rich by a higher-than-actual TP reading.

Step 1-8:

Step 9-16:

Troubleshooting