GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 6.6L 🢒 Ignition Relay Diagnosis

Circuit Description

The ignition relay supplies ignition voltage to the following components:

    • The glow plugs
    • The fuel injection control module (FICM)
    • The engine control module (ECM)
    • The fuel rail pressure regulator
    • The mass air flow (MAF) sensor
    • The fuel heater
    • The A/C compressor relay
    • The daytime running lamps
    • The rear defogger

Diagnostic Aids

If the IGN relay fails open:

    • The scan data WILL be available.
    • The vehicle WILL crank, no start.
    • The dash indicator lights WILL illuminate.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests the ignition 1 relay control circuit from the ECM.

    2.

  2. This step isolates the circuit from the IGN relay. All of the circuits at the relay are good if the test lamp illuminates.

Step

Action

Yes

No

Schematic Reference : Power Distribution Schematics in Wiring Systems

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Turn OFF the ignition.
  2. Remove the underhood electrical center cover.
  3. Remove the IGN 1 relay with J 43244 Relay Puller Pliers.
  4. Probe the IGN 1 relay 12-volt switch supply circuit at the underhood electrical center terminal with the test lamp connected to a ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

Go to Step 3

Go to Step 8

3
  1. Turn ON the ignition, with the engine OFF.
  2. Probe the IGN 1 relay 12-volt coil supply circuit at the underhood electrical center with the test lamp connected to a ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 9

4

Probe the ignition 1 relay control circuit at the underhood electrical center with a test lamp connected to battery voltage. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

Go to Step 5

Go to Step 10

5

  1. Turn OFF the ignition.
  2. Jumper the IGN 1 relay switch supply circuit and the IGN 1 relay load circuit together using a fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems.
  3. Probe the following fuses with the test lamp connected to a ground:
    4. • The ECMRPV
    • The INJR B

Does the test lamp illuminate for all of the fuses listed?

Go to Step 6

Go to Step 13

6

Inspect for poor terminal contact at the IGN relay underhood electrical center connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

Go to Step  14

Go to Step  7

7

Replace the IGN 1 relay.

Did you complete the replacement?

Go to Step  14

--

8

Repair the open or short to ground in the 12-volt switch supply to the IGN 1 relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step  14

--

9

Repair the open or short to ground in the 12-volt coil supply circuit to the IGN 1 relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step  14

--

10

Test the ignition 1 relay control circuit for an open and repair as necessary. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step  14

Go to Step  11

11

Test for poor or intermittent connections at the ECM and repair as necessary. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step  14

Go to Step  12

12

Replace the ECM. Refer to Engine Control Module Replacement

Did you complete the replacement?

Go to Step  14

--

13

Replace the underhood electrical center.

Did you complete the replacement?

Go to Step  14

--

14
  1. Remove all test equipment except scan tool.
  2. Reconnect any disconnected components, fuses, etc.
  3. Turn ignition OFF for 30 seconds.
  4. Start the engine and operate vehicle.
  5. Observe the MIL, the vehicle performance, and driveability.

Does the vehicle operate normally, with no MIL illumination and no stored DTCs?

System OK

Go to Diagnostic Trouble Code (DTC) List