DTC P0300 and Engine Miss At Idle Due To A Leaking Intake Valve - Replace Cylinder With Valves - keywords CEL compression controls excessive high leakage leakdown low MIL misfire P0301 P0302 P0303

This PI Supercedes To Include A Request For Cylinder Leakage Test Results. Please Discard PIP3935A.

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

On rare occasions, a SES light and P0300 may be experienced due to a single cylinder misfire at idle that may or may not be felt. On vehicles built before the VIN breakpoints above, this may be due to non-uniform intake valve seat wear, preventing the intake valve from sealing properly. Vehicles built after these VIN breakpoints contain harder intake valve seats to prevent intake valve wear and leakage

Important: The engine misfires described in this PI, which occur as a result of the leaking intake valves mentioned above, will occur at idle. If the engine misfires do not occur at idle, this PI does not apply.

If the SI diagnostics do not isolate a cause for this concern, perform a cylinder leakage test as outlined in the "Cylinder Leakage Test" procedure in SI and document all leakage rates on the repair order. When performing the cylinder leakage test, it is very important to hold the crankshaft with the related piston at top dead center to ensure that the valves are fully closed or inaccurate results may be obtained. If an aftermarket leakdown tester is used, the instructions of the aftermarket tester should also be referenced.

If a leaking intake valve is found, follow the updated cylinder head replacement procedure in 06-06-01-017C and replace the cylinder head with part number 12611423, which contains harder intake valve seats to prevent future intake valve leakage. If this cylinder head part number ever supersedes to a new part number, it is acceptable to use the new part number as well. At this time, it may be necessary to set a SPAC case to obtain this updated cylinder head. This updated cylinder head assembly comes with new valves, valve springs, valve seals, valve retainers, and valve keepers. Inspect ALL of the other components from the original cylinder head and transfer them to their original locations on the new cylinder head if there is no problem found with any of them. If there is anything wrong with any of these components, replace them as necessary.

Important: If the vehicle is a 2006 model, install the latest PCM calibrations to complete the repair.

Important: The updated cylinder head replacement procedure outlined in 06-06-01-017C no longer requires removal of the oil pan, front cover, water pump, or crankshaft dampener. Before replacing a cylinder head by following 06-06-01-017C, also review PIP3940A, which contains some tips for using the lower timing gear tensioner holding tool (EN48464) that is mentioned in 06-06-01-017C

Important: If excessive intake valve leakage is found on a vehicle built after the VIN breakpoints above, repair the vehicle as outlined above and submit a product report by following 02-00-89-002F. Please include the cylinder leakage rates for each cylinder and any other details that may be useful to engineering.

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.