GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 TrailBlazer - 2WD 🢒 Engine 🢒 Engine Electrical 🢒 Powertrain Relay Diagnosis

Circuit Description

The powertrain 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 powertrain 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 (ODM). When the ECM commands the relay ON, the relay coil creates an electromagnetic field. This electromagnetic field overcomes the spring tension and pulls the armature contact into the stationary contact of the relay load circuit. The closing of the relay contacts allows current to flow from the battery to the following fuses:

    • The INJ A Fuse
    • The INJ B Fuse
    • The TAC fuse
    • The ENG 1 Fuse
    • The 02 A Fuse
    • The 02 B Fuse

When the ignition switch is turned to the OFF position, power is interrupted to the ODM in the ECM and the powertrain relay electromagnetic field collapses. This action allows the spring tension pulling on the armature to separate from the relay load circuit contact, which interrupts current flow to the fuses. If the powertrain relay fails to close, the engine will crank but will not run. The GMLAN and class II data communications will be available with the use of a CANdi module and scan tool. The powertrain relay will remain powered up for 5 seconds after the ignition switch is turned OFF. The powertrain relay system diagnosis table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test in Engine Electrical.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Electrical Center Identification Views in Wiring Systems, Engine Control Module Connector End Views , and Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Is DTC P0685, P0689, or P0690 also set?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Remove the underhood fuse block cover.
  3. Probe the following fuses with a test lamp that is connected to a good ground:
    4. • The INJ A Fuse
    • The INJ B Fuse
    • The TAC fuse
    • The ENG 1 Fuse
    • The 02 A Fuse
    • The 02 B Fuse
    • Refer to Troubleshooting with a Test Lamp in Wiring Systems.

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

Go to Step 6

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Remove the powertrain relay from the underhood fuse block with the J 43244 Relay Puller Pliers. Refer to Relay Replacement in Wiring Systems.
  3. Connect a 20-amp fused jumper wire from the battery positive voltage terminal for the powertrain relay armature at the underhood fuse block, to the relay load circuit terminal at the underhood fuse block. Refer to Using Fused Jumper Wires in Wiring Systems.
  4. Probe the following fuses with a test lamp that is connected to a good ground:
    5. • The INJ A Fuse
    • The INJ B Fuse
    • The TAC fuse
    • The ENG 1 Fuse
    • The 02 A Fuse
    • The 02 B Fuse

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

Go to Intermittent Conditions

Go to Step 5

5

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 6

--

6
  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 7

Go to Engine Cranks but Does Not Run

7
  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 in Vehicle DTC Information

System OK