GM Service Manual Online
For 1990-2009 cars
Makes 🢒 Chevrolet 🢒 2004 🢒 C-Series Medium Duty Truck C6/7/8 - Mexico 🢒 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 relay fails close:

    • Scan data WILL be available.
    • Vehicle WILL crank, no start.
    • Instrument panel indicator lights WILL illuminate.

Test Description

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

  1. This step is testing for battery positive voltage supply, hot at all times, to the IGN relay switching contacts.

    2.

  2. This step is testing for battery positive voltage supply, hot in Run and Start, to the coil of the IGN relay.

    3.

  3. This step is testing the IGN relay coil ground circuit.

    4.

  4. This step is testing the IGN relay load circuit feed to circuit breakers and fuses.

Step

Action

Yes

No

Schematic Reference: Power Distribution Schematics , Ground Distribution Schematics in Wiring Systems, and 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. Disconnect the ignition relay electrical connector.
  3. Probe the ignition relay battery positive voltage circuit at the ignition relay electrical connector with a test lamp connected to a good 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 ignition relay ignition 1 voltage circuit at the ignition relay electrical connector with a test lamp connected to a good 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 relay ground circuit 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 ignition relay battery positive voltage circuit and the ignition relay load circuit together using a fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems.
  3. Remove the following circuit breakers from the instrument panel fuse block:
    4. • ENG 1
    • ENG 2
    • ENG 3
  4. Probe the IGN relay switch B+ feed terminals in the fuse block for the above circuit breakers with a test lamp connected to a ground.

Does the test lamp illuminate for all circuit terminals?

Go to Step 6

Go to Step 11

6

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

Did you find and correct the condition?

Go to Step 12

Go to Step 7

7

Replace the ignition relay.

Did you complete the replacement?

Go to Step 12

--

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 12

--

9

Repair the open or short to ground in the ignition 1 voltage circuit to the ignition relay.

Did you complete the repair?

Go to Step 12

--

10

Repair the open circuit or high resistance in the ignition relay coil ground circuit.

Did you complete the repair?

Go to Step 12

--

11

Repair the open circuit or high resistance in the ignition relay load circuit.

Did you complete the repair?

Go to Step 12

--

12
  1. Remove all test equipment except the scan tool.
  2. Reconnect any disconnected components, circuits, breakers, etc.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine and operate the vehicle.
  5. Observe the 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