Circuit/System Testing

WARNING: This page is about a different car, the 2007 GMC Sierra, 2007 GMC Cab & Chassis Sierra, 2007 Chevrolet Silverado, and 2007 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Crank the engine for 15 seconds.
Observe the vehicle DTC information with a scan tool.
- If any DTCs are set, then repair those DTCs first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
With the ignition ON and the engine OFF, test the fuses that are supplied ignition 1 voltage by the powertrain relay. The test lamp should illuminate ON for each test point of the fuses.
- If the test lamp does not illuminate on, for at least one test point of each fuse, refer to DTC P0685, P0689, or P0690 .
Crank the engine for 15 seconds. Observe the engine speed parameter with a scan tool.
- If engine RPM is not indicated, refer to DTC P0335 or P0336 .
Install a spark plug tester onto one ignition module/coil assembly, on each bank of the engine.
Observe both spark plug testers.

IMPORTANT: An erratic or weak spark is considered a no spark condition.

Crank the engine for 15 seconds. The ignition coil secondary voltage should be observed across the gap of both spark plug testers.
- If the ignition coil secondary voltage is not observed, is inconsistent, or weak on either spark plug tester, refer to Electronic Ignition (EI) System Diagnosis .
With the ignition ON and the engine OFF, command the fuel pump ON and OFF with the scan tool. The fuel pump should energize when commanded ON, and de-energize when commanded OFF.
- If the fuel pump does not turn ON and OFF, refer to Fuel Pump Electrical Circuit Diagnosis (with LMG, LC9, or LY6) or Fuel Pump Electrical Circuit Diagnosis (FPCM) .
Turn OFF the ignition.
Install the J 34730-1A Fuel Pressure Gage. With the ignition ON and the engine OFF, command the fuel pump ON several times with the scan tool. Refer to Fuel System Diagnosis (with LMG, LC9, or LY6) or Fuel System Diagnosis (FPCM) for the fuel pressure specification.
Inspect for the following conditions:
- Compare the actual engine coolant temperature to the ECT parameter
- Filter and air intake system for restrictions and obstructions
- Test the fuel for contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
- Inspect the spark plugs-Refer to Spark Plug Inspection .
- Test the exhaust system for restrictions-Refer to Restricted Exhaust .
- Engine mechanical conditions, such as worn timing chain, sprocket gears, low compression, etc-Refer to Symptoms - Engine Mechanical .