GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Terrain 🢒 DTC 🢒 DTC P2178, P2188, or P2192

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 provide an overview of each diagnostic category.

DTC Descriptors

DTC P2178 : Fuel Trim System Rich at Cruise or Accel

DTC P2188 : Fuel Trim System Rich at Idle

DTC P2192 : Fuel Trim System Rich at Higher Load

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 trim fuel delivery adjustments. If the HO2S indicate a lean condition, fuel trim values will be above 0 percent. If the O2S indicate a rich condition, fuel trim values will be below 0 percent. 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

    • The engine load is between 27-85 percent.
    • The fuel system is in closed loop.
    • The engine coolant temperature (ECT) is more than 70°C (158°F).
    • The intake air temperature (IAT) is less than 80°C (176°F).
    • The evaporative emission (EVAP) canister purge solenoid valve is not enabled.
    • The amount of air flow into the engine is between 50-350 kg/h.
    • The above conditions are met for more than 30 seconds.

P2188

    • The engine speed is less than 1000 RPM.
    • The fuel system is in closed loop.
    • The engine coolant temperature (ECT) is more than 70°C (158°F).
    • The intake air temperature (IAT) is less than 80°C (176°F).
    • The evaporative emission (EVAP) canister purge solenoid valve is not enabled.
    • The amount of air flow into the engine is less than 23 kg/h.
    • The above conditions are met for more than 20 seconds.

P2192

    • The engine speed is more than 1200 RPM.
    • The engine load is between 10-20 percent.
    • The fuel system is in closed loop.
    • The engine coolant temperature (ECT) is more than 70°C (158°F).
    • The intake air temperature (IAT) is less than 80°C (176°F).
    • The evaporative emission (EVAP) canister purge solenoid valve is not enabled.
    • The above conditions are met for more than 20 seconds.

Conditions for Setting the DTC

DTC P2178

The ECM detects that the Total Fuel Trim Avg. is less than a predetermined amount during cruise or accel.

DTC P2188

The ECM detects that the Total Fuel Trim Avg. is less than a predetermined amount during idle.

DTC P2192

The ECM detects that the Total Fuel Trim Avg. is less than a predetermined amount during a higher load.

Action Taken When the DTC Sets

DTCs P2178, P2188, and P2192 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P2178, P2188, and P2192 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 .
    • Review the Freeze Frame/Failure Records with a scan tool.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Controls Connector End Views
    •  Engine Control Module 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

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification
  1. If there are other DTCs set besides DTC P2178, P2188, or P2192, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnosis the applicable DTC.
  2. Ignition ON, observe the scan tool barometric pressure (BARO) sensor pressure parameter and compare the reading on the scan tool to the barometric pressure table. Refer to Altitude Versus Barometric Pressure .
  3. Engine at normal operating temperature, observe the scan tool Total Fuel Trim Avg. parameter . The reading should be between -22 to +23 percent.

Circuit/System Testing
  1. Verify none of the following conditions exist:
    2. • A collapsed air intake duct
    • A restricted air filter element .
    • 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 .
  2. If all conditions test normal, refer to Diagnostic Aids.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Heated Oxygen Sensor 1 Replacement
    •  Heated Oxygen Sensor 2 Replacement
    •  Control Module References for engine control module replacement, setup, and programming