GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Uplander Ext. 🢒 Engine 🢒 Engine Controls - 3.5L (LX9) 🢒 Powertrain Relay Diagnosis

Circuit Description

Ignition Main Relay

When the ignition switch is turned to the Run or Start position, voltage is supplied to the body control module (BCM). The BCM supplies 12 volts on the ignition 1 voltage output to the ignition main relay.

The ignition main relay supplies voltage to the following components:

    • Crank relay
    • Air conditioner (A/C) compressor clutch
    • Transaxle internal mode switch (IMS)
    • HVAC module
    • Cruise control system
    • Powertrain control module (PCM) ignition 1 voltage input

Any condition which interrupts the voltage source or ground source to and from the ignition main relay will prevent the engine from cranking. Following the Diagnostic System Check - Vehicle for loss of communication with the ignition main relay in mind will assist the technician in quickly identifying the cause. The ignition main relay is normally an open relay.

Powertrain Relay

When the ignition 1 voltage input to the PCM is received, the PCM activates the output driver module for the powertrain relay. The powertrain relay supplies voltage to various sensors and components necessary for the engine operation.

The ignition main relay supplies voltage to the following components:

    • The ETC fuse
    • The ELEC IGN fuse
    • The FUEL INJ fuse
    • The EMIS/AWD fuse
    • The ENG SNSR/EVAP fuse

For both relays, 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 powertrain 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 powertrain relay table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test in Engine Electrical.

Step

Action

Yes

No

Schematic Reference: Ground Distribution Schematics and Power Distribution Schematics in Wiring Systems 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 in Vehicle DTC Information

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 ETC fuse
    • The ELEC IGN fuse
    • The FUEL INJ fuse
    • The EMIS/AWD fuse
    • The ENG SNSR/EVAP fuse

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

Go to Step 3

Go to Step 4

3
  1. Turn OFF the ignition.
  2. Probe the following fuses with a test lamp that is connected to a good ground.
    3. • The ETC fuse
    • The ELEC IGN fuse
    • The FUEL INJ fuse
    • The EMIS/AWD fuse
    • The ENG SNSR/EVAP fuse

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

Go to Step 8

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

4
  1. Turn OFF the ignition.
  2. Remove the powertrain relay from the underhood junction block with the J 43244 Relay Puller Pliers and Relay Replacement in Wiring Systems.
  3. Probe each battery positive voltage cavities 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 each of the cavity test points?

Go to Step 5

Go to Step 8

5
  1. Turn OFF the ignition.
  2. Disconnect the ignition switch electrical connector.
  3. Connect a 20-amp fused jumper wire from the battery positive voltage cavity to the load side of the powertrain relay cavity . Refer to Using Fused Jumper Wires in Wiring Systems.
  4. Probe the following fuses with a test lamp that is connected to ground:
    5. • The ETC fuse
    • The ELEC IGN fuse
    • The FUEL INJ fuse
    • The EMIS/AWD fuse
    • The ENG SNSR/EVAP fuse

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

Go to Step 7

Go to Step 6

6

Test the powertrain relay load circuit of the underhood fuse block between the powertrain relay and the fuses for an open. Refer to Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

7

Inspect the underhood fuse block for loose or corroded terminals. Refer to Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 10

Go to Step 9

8

Repair the open in the powertrain relay battery voltage circuit at the underhood fuse block for an open. Refer to Circuit Testing in Wiring Systems.

Did you complete the repair?

Go to Step 10

--

9

Replace the powertrain relay. Refer to Circuit Protection - Fusible Links in Wiring Systems.

Did you complete the replacement?

Go to Step 10

--

10
  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 11

Go to Engine Cranks but Does Not Run

11
  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