GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Classic - 4WD 🢒 Power and Signal Distribution 🢒 Wiring Systems and Power Management 🢒 Ignition Relay Diagnosis

Circuit Description

The ignition relay is a normally open relay. The relay armature is held in the open position by spring tension. When the ignition switch is turned to the run or start position, current will flow through the relay coil. A wire connected to the other end of the relay coil completes the path to ground. The electomagnetic field created by the relay coil, overcomes the spring tension and moves the armature allowing the relay contacts to close. The closed relay contacts allow current to flow from the battery to the following fuses:

    • The PCM 1 fuse
    • The ETC/ECM fuse
    • The INJ 1 fuse
    • The INJ 2 fuse
    • The SBA fuse, if equipped

When the ignition switch is turned to the OFF position, the electromagnetic field collapses. This action allows the spring tension to move the armature away from the relay contacts, which interrupts current flow to the fuses.

If the ignition relay fails to close, the engine will crank, but will not run. The class 2 communications will be available with the use of a scan tool.

The ignition relay table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test.

Step

Action

Yes

No

Schematic Reference: Power Distribution Schematics and Ground Distribution Schematics and Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn ON the ignition, with the engine OFF.
  2. Remove the underhood junction block cover.
  3. Probe the following fuses with a test lamp that is connected to a good ground:
    4. • The PCM 1 fuse
    • The ETC/ECM fuse
    • The INJ 1 fuse
    • The INJ 2 fuse
    • The SBA fuse, if equipped--Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate on at least one test point of each fuse?

Go to Step 3

Go to Step 10

3

  1. Turn OFF the ignition.
  2. Probe both test points of the PCM 1 fuse with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate on either test point of the fuse?

Go to Step 4

Go to Step 30

4

  1. Turn OFF the ignition.
  2. Remove the ignition relay from the underhood junction block with the J 43244 Relay Puller Pliers. Refer to Relay Replacement.

    3. Notice: Refer to Test Probe Notice in the Preface section.

  3. Probe the ignition 1 voltage circuit of the ignition relay at the underhood junction block with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate?

Go to Step 7

Go to Step 5

5

Test the relay load bus bar of the underhood junction block between the ignition relay and the fuses to the circuit components for a short to battery positive voltage. Refer to Circuit Testing.

Did you find a condition?

Go to Step 29

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Remove the following fuses from the underhood junction block:
    3. • The PCM 1 fuse
    • The ETC/ECM fuse
    • The INJ 1 fuse
    • The INJ 2 fuse
    • The SBA fuse, if equipped
  3. Probe the above fuse terminals in the underhood junction block with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate at any of the fuse terminals?

Go to Diagnostic System Check - Vehicle

Go to Step 27

7
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection.
  3. Disconnect the underhood junction block electrical connector that contains the ignition 1 voltage circuit for the ignition relay.
  4. Disconnect the ignition switch electrical connector that contains the ignition 1 voltage circuit for the ignition relay.
  5. Connect the negative battery cable to the battery.
  6. Test the ignition 1 voltage circuit for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

Go to Step 30

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Probe the ignition 1 voltage terminal on the ignition switch side of the ignition switch electrical connector with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate?

Go to Step 28

Go to Step 9

9

Test the ignition 1 voltage bus bar circuit in the underhood junction block for a short to battery positive voltage. Refer to Circuit Testing.

Did you find a condition?

Go to Step 29

Go to Step 27

10
  1. Turn OFF the ignition.
  2. Inspect the 40-amp IGN B fuse in the underhood junction block. Refer to Circuit Protection - Fuses.

Is the fuse open?

Go to Step 11

Go to Step 18

11
  1. Remove the 40-amp IGN B fuse from the underhood junction block.

    2. Notice: Refer to Test Probe Notice in the Preface section.

  2. Probe both fuse terminals in the underhood junction block with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate on at least one fuse terminal?

Go to Step 12

Go to Step 17

12

Test the ignition 1 voltage circuit between the ignition switch and the underhood junction block for a short to ground. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

Go to Step 30

Go to Step 13

13

Test the ignition switch assembly for a short to ground. Refer to Circuit Testing.

Did you find a condition?

Go to Step 28

Go to Step 14

14

Test the battery positive voltage circuit between the underhood junction block and the ignition switch for a short to ground. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

Go to Step 30

Go to Step 15

15

Test the battery positive voltage bus bar circuit of the underhood junction block between the 40-amp IGN B fuse and the ignition switch for a short to ground.

Did you find a condition?

Go to Step 29

Go to Step 16

16

Test the ignition 1 voltage bus bar circuit of the underhood junction block that contains the ignition relay for a short to ground.

Did you find a condition?

Go to Step 29

Go to Step 27

17
  1. Turn OFF the ignition.
  2. Probe the mounting stud for the battery positive cable at the underhood junction block with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate?

Go to Step 29

Go to Diagnostic System Check - Vehicle .

18
  1. Turn OFF the ignition.
  2. Remove the ignition relay with the J 43244 from the underhood junction block. Refer to Relay Replacement.

    3. Notice: Refer to Test Probe Notice in the Preface section.

  3. Probe the battery positive voltage circuit of the ignition relay at the underhood junction block with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate?

Go to Step 19

Go to Step 29

19
  1. Turn ON the ignition, with the engine OFF.
  2. Probe the ignition 1 voltage circuit of the ignition relay at the underhood junction block with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate?

Go to Step 23

Go to Step 20

20
  1. Turn OFF the ignition.
  2. Test the ignition 1 voltage circuit between the ignition switch and the underhood junction block for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

Go to Step 30

Go to Step 21

21

Test the ignition switch assembly for a high resistance or for an open. Refer to Circuit Testing.

Did you find a condition?

Go to Step 28

Go to Step 22

22

Test the battery positive voltage circuit between the ignition switch and the underhood junction block for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

Go to Step 30

Go to Step 29

23
  1. Turn ON the ignition, with the engine OFF.
  2. Probe the coil ground circuit of the ignition relay at the underhood junction block with a test lamp that is connected to battery voltage. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp.

Does the test lamp illuminate?

Go to Step 25

Go to Step 24

24
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection.
  3. Disconnect the underhood junction block electrical connectors.
  4. Test the coil ground circuit of the ignition relay at the underhood junction block electrical connector for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

Go to Step 30

Go to Step 29

25
  1. Turn OFF the ignition.
  2. Jumper the ignition relay battery positive voltage circuit and the ignition relay load circuit together at the underhood junction block with a 20-amp fused jumper wire. Refer to Using Fused Jumper Wires.
  3. Probe the following fuses with a test lamp that is connected to a good ground:
    4. • PCM 1
    • ETC/ECM
    • INJ 1
    • INJ 2
    • SBA, if equipped

Does the test lamp illuminate on at least one test point of each fuse?

Go to Step 26

Go to Step 29

26

Test for an intermittent and for a poor connection at the underhood junction block, ignition relay connector location. Refer to Testing for Intermittent Conditions and Poor Connections.

Did you find a condition?

Go to Step 29

Go to Step 27

27

Replace the ignition relay. Refer to Relay Replacement.

Did you complete the replacement?

Go to Step 30

--

28

Replace the ignition switch. Refer to Ignition and Start Switch Replacement.

Did you complete the replacement?

Go to Step 30

--

29

Replace the underhood electrical center. Refer to Underhood Electrical Center or Junction Block Replacement.

Did you complete the replacement?

Go to Step 30

--

30
  1. Replace any open fuses.
  2. Turn OFF the ignition for 30 seconds.
  3. Attempt to start the engine.

Does the engine start and run?

Go to Step 31

Go to Engine Cranks But Does Not Run

31
  1. Clear the DTCs with a scan tool.
  2. Operate the vehicle for 5 minutes.

Does a DTC set during this ignition cycle?

Go to Diagnostic Trouble Code (DTC) List - Vehicle .

System OK