2009 Chevy 2500HD 6.0L Misfire Diagnosis: Finding the Root Cause

Initial Diagnosis and Codes

• 💡 A 2009 Chevy 2500HD with a 6.0L V8 presented with a severe misfire and flashing check engine light, towed in after another experienced mechanic was stumped.
• 🔍 Initial scan revealed codes for low voltage on bank 2 O2 sensors, a P0300 (random misfire), and an EVAP leak, but the primary concern was the severe misfire affecting multiple cylinders.
• 📊 Misfire history indicated cylinders 2, 4, 6, and 8 were affected, but current misfire data was not initially registering.

Investigating the Misfire

• ⛽ The truck reeked of gasoline, and fuel trims on bank 2 were maxed out at +30%, indicating a significant fueling issue or lack of combustion.
• ⚡ Despite the severe symptoms, unplugging all four ignition coils on bank 2 resulted in no change in engine operation, and the truck only set coil primary circuit codes after this test.
• 🚫 No spark was detected from the ignition coils, suggesting a lack of spark across the entire bank.

Ground Circuit Failure

• 🛠️ Testing revealed power at the coils, but the black wire, identified as the ground circuit (G102), was found to be corroded and not providing a proper ground.
• ✅ Jumping a temporary ground to the coil pack restored spark, and the engine immediately began running smoothly, indicating the ground circuit was the root cause of the misfire.
• 💨 After fixing the ground, the exhaust was heavily saturated with fuel, causing significant fumes and smoke, which gradually cleared.

Secondary Issue: Coolant Temp Sensor

• ⚠️ After the misfire was resolved, a new issue arose: an engine coolant temp circuit high code, indicating an open circuit.
• 🔌 Upon inspection, the wire to the coolant temperature sensor was found to be broken directly at the sensor connector, likely due to the truck's corroded condition.
• ⏳ A replacement connector was ordered, and the repair was deemed necessary due to the vehicle's overall deteriorated state, particularly around the engine bay and chassis.

Diagnostic Learnings

• 🧠 The video highlights how a complete lack of combustion on an entire bank can render O2 sensors nearly useless for diagnosis, as they will read lean due to the lack of exhaust gases.
• 💡 In such cases, a more