Component Testing

WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Relay Test

Ignition OFF, disconnect the rear defog relay.
Test for 60-180 ohms between terminals 85 and 86.
- If not within the specified range, replace the relay.
Test for infinite resistance between the following terminals:
- 30 and 86
- 30 and 87
- 30 and 85
- 85 and 87
- If not the specified value, replace the relay.
Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.
- If greater than the specified range, replace the relay.

Rear Window Defogger Grid Test

Ignition ON, turn on the rear window defogger.
Verify that a test lamp illuminates between each rear window defogger grid line and ground. The test lamp should be off when testing at the ground side of the grid and get brighter as the test lamp moves closer to the voltage supply side of the grid. The test lamp should be dim when testing each grid line in the middle.
- If the test lamp remains bright at the middle of the grid line, test for an open between the test point and the ground side of the grid.
- If the test lamp remains off at the middle of the grid line, test for an open between the test point and the voltage supply side of the grid.