Circuit Description
The main relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the armature contact at all times. The engine control module (ECM) supplies the ground path to the relay coil control circuit, via an internal integrated circuit, called an output driver module. When the ECM commands the relay ON, ignition 1 voltage is supplied to the ECM through the V8 ECM fuse in the underhood fuse block. This ignition 1 voltage input to the ECM provides the ignition power for the ECM circuitry, and is also used to confirm that the main relay has closed. A voltage more than 10 volts indicates a short to battery positive voltage in the ignition 1 voltage circuit to the ECM. This DTC will set when the ECM detects more than 10 volts on the ignition 1 voltage circuit to the ECM, after the ignition switch is turned OFF.
Conditions for Running the DTC
The battery voltage is greater than 11 volts for more than 1.5 seconds with the ignition OFF.
Conditions for Setting the DTC
The ECM detects greater than 10 volts on the ignition 1 voltage circuit for more than 125 milliseconds.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| • | The main relay will remain powered up for 15 seconds after the ignition switch is turned OFF. |
| • | This diagnostic table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test in Engine Electrical. |
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views and Engine Controls Connector End Views | ||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||
2 |
Did the DTC fail this ignition? | -- | Go to Step 3 | Go to Intermittent Conditions | ||||||||||
3 |
Does the test lamp illuminate on either test point of the fuse? | -- | Go to Step 4 | Go to Step 7 | ||||||||||
4 |
Does the test lamp illuminate on either test point of the fuse? | -- | Go to Step 5 | Go to Step 10 | ||||||||||
5 |
Notice: Refer to Test Probe Notice in the Preface section.
Does the test lamp go out when a relay is removed? | -- | Go to Step 13 | Go to Step 6 | ||||||||||
6 |
Notice: Refer to Test Probe Notice in the Preface section.
Does the test lamp go out when a fuse is removed? | -- | Go to Step 11 | Go to Step 15 | ||||||||||
7 | Measure the resistance from terminal #30 of the main relay to terminal #87 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems. Does the DMM display the specified value? | ∞ ohms | Go to Step 8 | Go to Step 12 | ||||||||||
8 | Measure the resistance from terminal #30 of the main relay to terminal #85 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems. Does the DMM display the specified value? | ∞ ohms | Go to Step 9 | Go to Step 12 | ||||||||||
9 | Measure the resistance from terminal #85 of the main relay to terminal #87 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems. Does the DMM display the specified value? | ∞ ohms | Go to Intermittent Conditions | Go to Step 12 | ||||||||||
10 | Test for shorted terminals and poor connections at the ECM electrical connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Micro .64 Connectors in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14 | ||||||||||
11 | Repair the short to battery positive voltage in the ignition 1 voltage circuit that caused the test lamp to go out when the fuse for that circuit was removed. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- | ||||||||||
12 | Replace the main relay. Refer to Relay Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||||||
13 | Replace the relay that caused the test lamp to go out when the relay was removed from the underhood fuse block. Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||||||
14 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||||||
15 | Replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||||||
16 |
Did the DTC fail this ignition? | -- | Go to Step 3 | Go to Step 17 | ||||||||||
17 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||
