GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC T-Series Medium Duty Truck F6/F7/F8 🢒 DTC 🢒 DTC P2920

Circuit Description

The engine control module (ECM) main relay is energized when the ECM receives an ignition switch ON signal. If the ECM detects the ECM main relay has been ON since the ignition switch was turned OFF, this DTC will set.

Conditions for Running the DTC
    • The ignition is OFF.
    • The engine is stopped.

Conditions for Setting the DTC

The ECM detects that the ECM main relay has been ON, high voltage, for 5 seconds or more since the ignition switch was turned OFF.

Action Taken When the DTC Sets
    • The ECM does not illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.

Condition for Clearing the DTC
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • If an intermittent condition is suspected, the following may cause an intermittent:
       - Poor connections
       - A mis-routed harness
       - Rubbed through wire insulation
       - Broken wire inside the insulation
    • Inspect for the following conditions:
       - Poor connection at ECM--Inspect the harness connectors for the following conditions:
   • Backed-out terminals
   • Improper mating
   • Broken locks
   • Improperly formed or damaged terminals
   • Poor terminal to wire connection
       - Damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the Engine Coolant Temperature display on the scan tool while moving the connectors and the wiring harness related to the sensor. A change in the display will indicate the location of the fault.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Observe the Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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.

Did the DTC fail this ignition?

Go to Step 3

Go to Diagnostic Aids

3
  1. Turn OFF the ignition.
  2. Disconnect the main relay.
  3. Inspect for poor connections at the harness connector of the main relay.
  4. Repair or replace the main relay, as necessary.

Did you find and correct the condition?

Go to Step 7

Go to Step 4

4
  1. Test the signal circuit between the engine control module (ECM) and the ECM main relay to ensure the ECM main relay control circuit is shorted to the ground circuit.
  2. Repair the circuits, as necessary.

Did you find and correct the condition?

Go to Step 7

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Inspect for connections at the harness connector of the ECM.
  4. Repair the connections, as necessary.

Did you find and correct the condition?

Go to Step 7

Go to Step 6

6

Important: The new ECM must be programmed.

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data .

Did you complete the replacement?

Go to Step 7

--

7
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 8

8

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK