P0172
DTC P0172 or P2096 (LUW)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors
DTC P0172
- Fuel Trim System Rich
DTC P2096
- Post Catalyst Fuel Trim System Low 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. During open loop, the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During closed loop, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0%. If the 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 HO2S voltage signals. The long term fuel trim makes rough adjustments in order to maintain an optimal air/fuel ratio. A block of memory cells contain information arranged in combinations of engine speed and engine load for a full range of vehicle operating conditions. The long term fuel trim diagnostic is based on an average of cells currently being used. The ECM selects the cells based on engine speed and load. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if more vapor than the customer may desire from the evaporative emission (EVAP) canister is causing a rich condition.
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 heated oxygen sensor (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
* DTCs P0030, P0053, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0114, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P015A, P015B, P0201, P0202, P0203, P0204, P0222, P0223, P0300, P0301, P0302, P0303, P0304, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P0506 and P0507 are not set.
* The engine is in Closed Loop.
* The long term fuel trim is enabled.
* The catalyst diagnostic intrusive test, post HO2S diagnostic intrusive test, EVAP leak test and device controls are not active.
* The engine coolant temperature (ECT) is between -20 to +150°C (-4 to +302°F).
* The intake air temperature (IAT) is between -20 to +150°C (-4 to +302°F).
* The manifold absolute pressure (MAP) is between 10-255 kPa (1.5-37 PSI).
* The mass air flow (MAF) is between 1-512 g/s.
* The engine speed is between 400-7 000 RPM.
* The barometric pressure (BARO) is greater than 70 kPa (10 PSI).
* This DTC runs continuously when the above conditions are met.
P2096
* The fuel control intrusive diagnostics are not active.
* The long term secondary fuel trim is enabled.
* This DTC runs continuously when the above conditions are met for greater than 1 s.
Conditions for Setting the DTC
P0172
* The ECM determines if the fuel control system is in a rich condition, based on the filtered long-term and short-term fuel trim metric.
P2096
* The ECM determines if the post catalyst HO2S based fuel control system has been unable to adapt to a rich exhaust gas condition for too long.
Action Taken When the DTC Sets
DTCs P0172 and P2096 are Type B DTC.
Conditions for Clearing the DTC
DTCs P0172 and P2096 are Type B DTC.
Diagnostic Aids
* The system will become rich if a fuel injector is supplying too much fuel.
* A failed HO2S will not cause DTC P2096 to set without the occurrence of circuit related HO2S DTCs. Do not replace an HO2S to address this DTC.
* The post catalyst fuel trim diagnostic is very sensitive to heated oxygen sensor (HO2S) design. A non-OE sensor or an incorrect part number may cause a DTC to set.
* Certain aftermarket air filters may cause a DTC to set.
* Certain aftermarket air induction systems or modifications to the air induction system may cause a DTC to set.
* Certain aftermarket exhaust system components may cause a DTC to set.
Reference Information
Schematic Reference
Engine Controls Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
Note: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system 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/traction control system indicators.
1. Verify that other DTCs are not set.
• If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
2. The normal scan tool Short Term Fuel Trim parameter should be between +10 to -10%, with near 0% the optimum, with the engine running at operating temperature.
3. The scan tool Long Term Fuel Trim parameter should be between +10 to -10%, with near 0% the optimum, with the engine running at operating temperature.
• If the values are not less than -10%, inspect for the following:
* With the ignition ON and the engine OFF, observe the scan tool MAP Sensor parameter. The scan tool MAP Sensor pressure reading should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure Altitude Versus Barometric Pressure.
• If the B74 Manifold Absolute Pressure Sensor does not indicate the correct barometric pressure, refer to DTC P0106 (LUW) P0106.
* With the engine idling and the transmission in the park or neutral position, observe the scan tool MAP Sensor parameter. The scan tool MAP Sensor parameter should be between 19-42 kPa (2.8-6.1 PSI).
• If not within the specified range, refer to DTC P0107 or P0108 (LUW) P0107.
* With the engine idling and the transmission in the park or neutral position, observe the scan tool MAF Sensor parameter. The scan tool MAF Sensor parameter should be between 1 700-2 100 Hz.
• If not within the specified range, refer to DTC P0101 (LUW) P0101
* 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 EVAP control system for improper operation
* Excessive fuel pressure. Refer to Fuel System Diagnosis Fuel System Diagnosis
* Fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis Testing and Inspection.
* Malfunctioning fuel injectors. Refer to Fuel Injector Diagnosis Fuel Injector Diagnosis.
* The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system
• If you find any of the above conditions, repair as necessary.
4. If all conditions test normal, test the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical Symptoms - Engine Mechanical
5. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.
Repair Instructions
* Air Cleaner Assembly Replacement Service and Repair
* Air Cleaner Element Replacement Service and Repair
* Evaporative Emission Canister Replacement (Steel Tank) Service and Repair
* Fuel Injector Replacement Service and Repair
* Fuel Tank Fuel Pump Module Replacement (Steel Tank) Fuel Tank Fuel Pump Module Replacement (Steel Tank)
* Fuel System Cleaning Service and Repair
* Heated Oxygen Sensor Replacement - Sensor 1 Heated Oxygen Sensor Replacement - Sensor 1
* Heated Oxygen Sensor Replacement - Sensor 2 Heated Oxygen Sensor Replacement - Sensor 2
* Manifold Absolute Pressure Sensor Replacement Service and Repair
* Throttle Body Assembly Replacement Removal and Replacement
Repair Verification
Note: After repairs, use the scan tool fuel trim reset function in order to reset the long term fuel trim values.
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. DTCs 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 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 Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.
8. In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, perform the repair verification for DTC P0420. Refer to DTC P0420 (LUW) P0420.