Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2012CHEVY EXPRESS G2500, VAN PASSENGER, 4.8L ENG VIN AREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1251 (ENGINE CONTROL SYSTEM & FUEL - HYBRID (HP2) 6.0L (LFA) - DTC P0231 TO DTC P0690)DTC P0300-P0308CIRCUIT/SYSTEM TESTING
2012 Chevrolet Chevy Express G2500, Van Passenger, 4.8L Eng VIN A
Circuit/System Testing
2012 Chevrolet Chevy Express G2500, Van Passenger, 4.8L Eng VIN ASECTION 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.
- 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 .
IMPORTANT:
An erratic or weak spark is considered a no spark condition.
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.