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DTC P2178 or P2188

DTC P2178 or P2188

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 P2178

Fuel Trim System Rich at Cruise or Acceleration

DTC P2188

Fuel Trim System Rich at Idle

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 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 HO2S inputs are added and used by the ECM to calculate short and long term fuel delivery adjustments. If the HO2S indicate a lean condition, fuel trim values will be above 0 %. If the O2S indicate a rich condition, fuel trim values will be below 0 %. Short term fuel trim values change rapidly in response to the HO2S signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1.

Conditions for Running the DTC


P2178

• Before the ECM can report DTC P2178 failed, DTCs P0008, P0009, P0010, P0011, P0013, P0014, P0016, P0017, P0018, P0019, P0020, P0021, P0023, P0024, P0101, P0121, P0122, P0123, P0133, P0201, P0202, P0203, P0204, P0205, P0206, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0335, P0336, P0338, P0443, P0458, P0459, P0461, P0462, P0463, P2068 P2088, P2089, P2090, P2091, P2092, P2093, P2094, and P2095 must run and pass.

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

• The mass air flow is between 7-83 g/s.

• The throttle angle is less than 100 %.

• The engine load is between 17-55 %.

• The fuel system is in Closed Loop.

• The engine is not in decel fuel cut-off.

• The long term fuel trim is active.

• The engine coolant temperature (ECT) is greater than 60°C (140°F).

• The intake air temperature (IAT) is less than 61°C (142°F).

• The evaporative emission (EVAP) canister purge solenoid valve is not enabled.

• The fuel level is greater than 12 %.

• The amount of air flow into the engine is greater than 7,000 g.

• DTC P2178 runs continuously when the above conditions are met for at least 300 s.



P2188

• Before the ECM can report DTC P2188 failed, DTCs P0008, P0009, P0010, P0011, P0013, P0014, P0016, P0017, P0018, P0019, P0020, P0021, P0023, P0024, P0101, P0121, P0122, P0123, P0133, P0201, P0202, P0203, P0204, P0205, P0206, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0335, P0336, P0338, P0443, P0458, P0459, P0461, P0462, P0463, P2068 P2088, P2089, P2090, P2091, P2092, P2093, P2094, and P2095 must run and pass.

• The engine speed is between 480-1,001 RPM.

• The engine load is between 7-32 %.

• The MAF is between 1-8 g/s.

• The fuel system is in Closed Loop.

• The engine is not in decel fuel cut-off.

• The long term fuel trim is active.

• The engine coolant temperature (ECT) is greater than 60°C (140°F).

• The intake air temperature (IAT) is less than 61°C (142°F).

• The evaporative emission (EVAP) canister purge solenoid valve is not enabled.

• The fuel level is greater than 12 %.

• The amount of air flow into the engine is greater than 7,000 g.

• DTC P2188 runs continuously when the above conditions are met.


Conditions for Setting the DTC

P2178

The Total Fuel Trim Avg. is less than -22 %. The condition exists for 4 s or for a cumulative of 30 s.

P2188

The Total Fuel Trim Avg. is less than -40 %. The long term fuel trim Idle/Decel is less than -6 %. The condition exists for 4 s or for a cumulative of 30 s.

Action Taken When the DTC Sets

DTCs P2178 and P2188 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P2178 and P2188 are Type B DTCs.

Diagnostic Aids


• A fuel system delivery condition causes this DTC to set. Thoroughly inspect all items that cause a rich condition. Refer to Fuel System Diagnosis .

• Observe the Freeze Frame/Failure Records with a scan tool.


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


1. Check the DTC Info with a scan tool. Diagnostic trouble codes P2178 or P2188 must not be activated.

2. If there are other DTCs set besides DTC P2178 or P2188 refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnosis the applicable DTC.

3. Ignition ON, observe the BARO pressure parameter and compare the reading on the scan tool to the barometric pressure table. Refer to Altitude Versus Barometric Pressure .

4. If the BARO pressure is not within the range specified for your altitude, refer to DTC P2227, P2228, or P2229 (LAU) .

5. Engine at normal operating temperature, observe the Average Total Fuel Trim parameter with a scan tool. The Average Total Fuel Trim should be between -22 to +23 %.

6. If not within the specified range, inspect for the following conditions:

• A mass air flow sensor signal that is skewed-If the Short Term Fuel Trim parameter changes greater than 20 % when the MAF sensor is disconnected, refer to DTC P0101 .

• A collapsed air intake duct

• A restricted air filter element

• The MAF sensor for foreign objects.

• Excessive fuel in the crankcase-Change the oil as necessary.

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

• The engine control module grounds for being clean, tight, and in the correct locations

• Rich injectors-Refer to Fuel Injector Solenoid Coil Test .

• Restricted exhaust system-Refer to Symptoms - Engine Exhaust .

• An engine mechanical condition-Refer to Symptoms - Engine Mechanical .

7. 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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.