GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC K Sierra - 4WD 🢒 Engine 🢒 Engine Electrical 🢒 Ignition Relay Diagnosis

Circuit Description

The ignition relay supplies ignition voltage to the following components:

    • Fuel injectors
    • Ignition coils
    • Powertrain control module (PCM)
    • Alternator/Generator.

Diagnostic Aids

If the IGN relay fails to close:

    • Scan data will be available.
    • Vehicle will crank, no start.
    • Dash indicator lights will illuminate.

Test Description

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

  1. This step is testing the relay ground circuit.

    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.

    3.

  3. The open circuit will be between the splice and the IGN relay.

    4.

  4. Remove the underhood electrical center cover and inspect the circuits that are supplied a voltage by the IGN relay.

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. Turn OFF the ignition.
  2. Remove the underhood electrical center cover.
  3. Remove the IGN relay.
  4. Probe the IGN relay battery positive voltage circuit at the underhood electrical center terminal with the test lamp connected to a ground. Refer to Probing Electrical Connectors 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 relay ignition 1 voltage 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
  1. Turn ON the ignition, with the engine OFF.
  2. Probe the ignition main relay ground connector terminal with a test lamp connected to 12 volts.

Does the test lamp illuminate?

Go to Step 5

Go to Step 10

5
  1. Turn OFF the ignition.
  2. Jumper the IGN relay battery positive voltage circuit and the IGN relay load circuit together using a fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems.
  3. Probe the fuses for the following components with the test lamp connected to a ground.
    4. • ECM I
    • INJR A
    • INJR B

Does the test lamp illuminate for all fuses listed?

Go to Step 6

Go to Step 10

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 11

Go to Step 7

7

Replace the IGN relay.

Did you complete the replacement?

Go to Step 11

--

8

Repair the open or short to ground in the battery positive voltage supply to the IGN relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 11

--

9

Repair the ignition 1 voltage circuit to the IGN relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 11

--

10

Replace the underhood electrical center.

Did you complete the replacement?

Go to Step 11

--

11
  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 malfunction indicator lamp (MIL), 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