Circuit/System Testing

WARNING: This page is about a different car, the 2008 GMC Yukon and 2008 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.

IMPORTANT: You must perform the Circuit/System Verification first.

Ignition OFF, open the hood to disable the Auto-Stop function. Refer to Hybrid Modes of Operation Description .
Ignition ON, verify the scan tool hood position parameter displays Open.
- If the hood position does not display Open, refer to Diagnostic Trouble Code (DTC) List - Vehicle for DTC P254F.
Verify that the following conditions do not exist:
- The fuel injector wire harness electrical connectors are connected to the wrong fuel injectors. Refer to Engine Controls Schematics .
- Engine vacuum leaks
- Fuel pressure that is too low or too high-Refer to Fuel System Diagnosis .
- Contaminated fuel-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) .
- Restricted exhaust system-Refer to Restricted Exhaust .
- The cylinder deactivation system for misfire on either cylinders 1, 4, 6, or 7-Refer to Cylinder Deactivation (Active Fuel Management) System Diagnosis .
Measure the resistance of the spark plug wire and verify the condition of the spark plug wire. Refer to Ignition System Specifications and Spark Plug Wire Inspection .
- If the resistance value is not within the specified range or does not pass the inspection, replace the spark plug wire.
Install the spark plug wire to the ignition module/coil assembly.
Install the J 26792 to the spark plug wire boot.

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

Attempt to start the engine and observe the J 26792 . The spark plug tester should spark.
- If there is no spark, refer to Electronic Ignition (EI) System Diagnosis .
Ignition OFF, remove the spark plug from the misfiring cylinder. Verify that the following conditions do not exist with the spark plug:
- Gas, coolant, or oil fouled
- Cracked, worn, or incorrectly gapped-Refer to Spark Plug Inspection .
- If there is a condition with the spark plug, replace the spark plug.
Exchange the suspected spark plug with another cylinder that is operating correctly.
Operate the engine under the conditions in which the misfire occurred. This may include putting the engine under a load or allowing the engine to return to a cold condition. Observe the Misfire Current Counters with a scan tool. The misfire should not follow the spark plug exchange.
- If the misfire follows with the spark plug, replace the spark plug.
If all conditions test normal, test or inspect for the following:
- A lean or rich fuel injector-Refer to Fuel Injector Diagnosis (w/CH 47976) or Fuel Injector Diagnosis (w/J 39021 or Tech 2) .
- An engine mechanical condition-Refer to Symptoms - Engine Mechanical .