Diagnostic Aids
WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
If the glow plug relay is stuck in the ON position, check for proper operation of the glow plugs. When the glow plugs are commanded ON by the scan tool, an internal Engine Control Module (ECM) timer protects the glow plugs from damage by cycling them ON for 3 seconds and the OFF for 12 seconds. The glow plug relay battery feed wire nut at the relay should be tested for proper torque. The California glow plug system will send the following voltages, or signals to the ECM. See GLOW PLUG VOLTAGE table.
GLOW PLUG VOLTAGE
| Signal Voltage (Volts) | Glow Plugs Failed Open |
|---|---|
| 5.0-6.0 | None |
| 2.0-3.0 | 1 |
| 1.0-2.0 | 2 |
| 0.8-1.7 | 3 |
| Less Than 1.3 | 4 Or More |
An intermittent may be caused by the following:
- Poor connections, terminal tension.
- Rubbed-through wire insulation.
- Broken wire inside the insulation.
- A short to battery positive voltage on the glow plug relay control circuit.