Diagnostic Aids

A misfire may only occur when the engine is under a load or when the engine is cold.

A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect for the following possible sources:

• A tire or wheel that is out of round or out of balance
• Variable thickness brake rotors
• An unbalanced drive shaft
• Certain rough road conditions
• A damaged accessory drive component or belt
• A damaged reluctor wheel
• The Crankshaft Position System Variation Learn procedure may need to be performed.
• The 3.9L, RPO LGD, VIN code W, E85 compatible engines only, may use either American Society for Testing and Materials (ASTM) gasoline with 10 percent or less ethanol content or unleaded fuel containing 85 percent ethanol, or ASTM E85. Refer to Fuel System Description .
• The 3.9L, RPO LGD, VIN code W, E85 compatible engines only, over-estimation of the ethanol content will result in a rich shift of fuel trim values and under-estimation will result in a lean shift of fuel trim values. A misfire DTC may set if the learned alcohol content, Fuel Alcohol Content parameter, on the scan tool is different than the measured alcohol content in the vehicle such that values exceed failure threshold values. Refer to Fuel Composition Diagnosis .