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Home >> Buick >> 2004 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls 3.1L (Troubleshooting & Diagnosis) >> Engine Controls >> Ignition Relay Diagnosis >> Circuit Description

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 electromagnetic field created by the relay coil, overcomes the spring tension and moves the armature allowing the relay contact to close. The closed relay contacts allow current to flow from the battery to the following fuses:

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 in Engine Electrical.

Ignition Relay Diagnosis

Step Action Yes No
Schematic Reference:  Power Distribution Schematics  and  Ground Distribution Schematics  in Wiring Systems and  Engine Controls Schematics 
Connector End View Reference:  Engine Controls Connector End Views  or  Powertrain Control Module (PCM) Connector End Views 
1 Did you perform the Diagnostic System Check-Engine Controls? Go to Step 2  Go to Diagnostic System Check - Engine Controls
2
  1. Turn ON the ignition, with the engine OFF.
  2. Remove the underhood junction block cover.
  3. Probe the following fuses with the test lamp that is connected to a good ground:
Does the test lamp illuminate on at least one test point of each fuse?		 Go to Step 3  Go to Step 11 
3
  1. Turn OFF the ignition.
  2. Probe both test points of the ENG EMIS fuse with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp in Wiring Systems.
Does the test lamp illuminate on either test point of the fuse?		 Go to Step 4  Go to Step 36 
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 (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) in Wiring Systems.
  3. Probe both test points of the 10-amp PCM, BCM, U/H relay fuse in the instrument panel (I/P) fuse block with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp in Wiring Systems.
Does the test lamp illuminate on any of the fuse test points?		 Go to Step 8  Go to Step 5 
5 Test the ignition relay load circuit 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 in Wiring Systems.
Did you find a condition?		 Go to Step 35  Go to Step 6 
6
  1. Turn OFF the ignition.
  2. Remove the following fuses from the underhood junction block:
    • OXY SEN
    • ELEK IGN
    • F/INJR
    • TRANS
    • ENG EMIS
  3. Probe all these 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 in Wiring Systems.
Does the test lamp illuminate at any of the fuse terminals?		 Go to Step 7  Go to Step 32 
7
  1. Turn OFF the ignition.
  2. Remove the A/C clutch relay from the underhood junction block with the J 43244  .
  3. Probe both fuse terminals of the EMG EMIS fuse 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 in Wiring Systems.
Does the test lamp illuminate on either fuse terminal?		 Go to Diagnostic System Check - Engine Electrical in Engine Electrical Go to Step 34 
8
  1. Turn OFF the ignition.
  2. Disconnect the ignition switch electrical connector.
  3. Connect a 20-amp fuse jumper wire from the battery positive voltage circuit terminal at the ignition switch connector, to the corresponding terminal at the vehicle harness connector. Refer to Using Fused Jumper Wires in Wiring Systems.
  4. Probe the ignition 1 voltage circuit at 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 in Wiring Systems.
Does the test lamp illuminate?		 Go to Step 33  Go to Step 9 
9
  1. Remove the following fuses from the I/P fuse block:
    • TURN SIGNALS, CORN LPS
    • AIR BAG
    • CLUSTER
    • PCM, BCM, U/H RELAY
  2. Probe the ignition 1 voltage circuit of the ignition switch electrical connector that leads to the I/P fuse block, with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp in Wiring Systems.
Does the test lamp illuminate?		 Go to Step 30  Go to Step 10 
10
  1. Turn OFF the ignition.
  2. Disconnect the electrical connector at the underhood junction block that contains the ignition 1 voltage circuit of the ignition relay.
  3. Probe the ignition 1 voltage circuit of the ignition relay at the underhood junction block vehicle harness electrical connector with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp in Wiring Systems.
Does the test lamp illuminate?		 Go to Step 31  Go to Step 35 
11
  1. Turn OFF the ignition.
  2. Probe both test points of the 30-amp IGN 1 fuse 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 in Wiring Systems.
Does the test lamp illuminate on both test points of the fuse?		 Go to Step 15  Go to Step 12 
12 Does the test lamp illuminate on one test point of the 30-amp IGN 1 fuse? Go to Step 13  Go to Step 21 
13 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 in Wiring Systems.
Did you find and correct the condition?		 Go to Step 36  Go to Step 14 
14 Test the ignition 1 voltage circuit between the ignition switch and the 10-amp PCM, BCM, U/H relay fuse terminals in the I/P fuse block for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 36  Go to Step 33 
15
  1. Turn ON the ignition, with the engine OFF.
  2. Probe both test points of the 10-amp PCM, BCM, U/H relay fuse with a test lamp that is connected to a good ground. Refer to Circuit Testing in Wiring Systems.
Does the test lamp illuminate on both test point of the fuse?		 Go to Step 22  Go to Step 16 
16 Does the test lamp illuminate on one test point of the 10-amp PCM, BCM, U/H relay fuse? Go to Step 19  Go to Step 17 
17 Test the ignition 1 voltage circuit between the ignition switch and the PCM, BCM, U/H relay fuse for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 36  Go to Step 18 
18 Test the battery positive voltage circuit between the underhood junction block and the ignition switch for a high resistance or for an open. Refer to Circuit Testing in Wiring Systems.
Did you find and correct the condition?		 Go to Step 36  Go to Step 33 
19 Test the ignition 1 voltage circuit between the I/P fuse block and the underhood junction block for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 36  Go to Step 20 
20 Test the underhood junction block, ignition 1 voltage bus bar circuit to the ignition relay for a short to ground. Refer to Circuit Testing in Wiring Systems.
Did you find a condition?		 Go to Step 35  Go to Step 32 
21
  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 in Wiring Systems.
Does the test lamp illuminate?		 Go to Step 35  Go to Diagnostic System Check - Engine Electrical in Engine Electrical
22
  1. Turn OFF the ignition.
  2. Remove the ignition relay with the J 43244  from the underhood junction block.
  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 in Wiring Systems.
Does the test lamp illuminate?		 Go to Step 23  Go to Step 35 
23
  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 in Wiring Systems.
Does the test lamp illuminate?		 Go to Step 25  Go to Step 24 
24 Test the ignition 1 voltage circuit between the I/P fuse block and the underhood junction block for a high resistance or for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 36  Go to Step 35 
25
  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 in Wiring Systems.
Does the test lamp illuminate?		 Go to Step 27  Go to Step 26 
26
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnect/Connect Procedure in Engine Electrical.
  3. Disconnect the underhood junction block electrical connector that contains the relay coil ground circuit.
  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 in Wiring Systems.
Did you find and correct the condition?		 Go to Step 36  Go to Step 35 
27
  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 in Wiring Systems.
  3. Probe the following fuses with a test lamp that is connected to a good ground:
Does the test lamp illuminate on at least one test point of each fuse?		 Go to Step 28  Go to Step 35 
28
  1. Remove the A/C clutch relay from the underhood junction block with the J 43244  .
  2. Probe the ignition 1 voltage circuit of the A/C clutch relay with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp in Wiring Systems.
Does the test lamp illuminate?		 Go to Step 29  Go to Step 35 
29 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 in Wiring Systems.
Did you find a condition?		 Go to Step 35  Go to Step 32 
30 Repair the short to battery positive voltage in the ignition 1 voltage circuit between the ignition switch and the I/P fuse block. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 Go to Step 36  -
31 Repair the short to battery positive voltage in the ignition 1 voltage circuit between the I/P fuse block and the underhood junction block electrical connector. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 Go to Step 36  -
32 Replace the ignition relay. Refer to Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) in Wiring Systems.
Did you complete the replacement?		 Go to Step 36  -
33 Replace the ignition switch. Refer to Ignition Switch Replacement in Steering Wheel and Column.
Did you complete the replacement?		 Go to Step 36  -
34 Replace the A/C clutch relay. Refer to Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) in Wiring Systems.
Did you complete the replacement?		 Go to Step 36  -
35 Replace the underhood electrical center. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems.
Did you complete the replacement?		 Go to Step 36  -
36
  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 37  Go to Engine Cranks but Does Not Run 
37
  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 System OK
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