False Misfire at Steady Speed or Slight Deceleration - keywords 5.3L AFM decel cruise DTC engine LH6 MIL miss P0300 SES

This PI was revised to include repair information. Please discard PIP3828.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Vehicles equipped with the 5.3 LH6 (Active Fuel Management engine) may experience a SES light with trouble code P0300 found. This concern will occur when the vehicle is at a steady cruise speed or on a slight deceleration. The SES light will illuminate or flash with no driveability symptoms noticed. During diagnosis the Non-AFM cylinders (2, 3, 5, and 8) will show random/history misfire counts.

If the vehicle has a misfire that can be felt, this PI will not apply, and the current SI misfire diagnostics should be completed.

Please complete bulletin number 06-06-04-001A for "Service Engine Soon (SES) Light On/Diagnostic Trouble Code(s) (DTC) P0300, P0171 and P0174, Active Fuel Management Misfire Due to Fuel Injector Connectors Crossed/Swapped/Incorrectly Installed", has been completed.

The customer concern of random or false misfire must be verified on a test drive. The description/verification of the concern will be a misfire trouble code/SES light on only during a steady cruise speed, or a slight deceleration.

There was a new calibration released on 8/6/2006 to address a SES light on, and a false DTC P0300. This calibration should only be used to repair a trouble code P0300 when it sets with no driveability symptoms. Update the vehicle ECM with the new calibration named "New software with diagnostic enhancements for DTC P0300 occurring in four cylinder mode at 60 to 75 mph" and evaluate repairs.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.