DTC P0300 And Engine Miss At Idle Due To A Leaking Intake Valve - Replace Cylinder Head With Valves - keywords CEL compression controls excessive high leakage leakdown low MIL misfire P0301 P0302
| Subject: | DTC P0300 and Engine Miss at Idle due to a Leaking Intake Valve - Replace Cylinder Head with Valves |
| Models: | 2004-2005 Chevrolet Colorado, GMC Canyon |
| with 3.5L Engine (VIN 6 - RPO L52) |
| 2006 Chevrolet Colorado, GMC Canyon |
| with 3.5L Engine (VIN 6 - RPO L52) |
| and Last 6 of VIN Less than 287698 |
| 2006 Hummer H3 |
| with 3.5L Engine (VIN 6 - RPO L52) |
| and Last 6 of VIN Less than 287591 |
This PI was superseded to refer to the latest versions of 07-06-01-011 and 06-06-01-017. Please discard PIP3935B.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
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 only. If the engine misfires occur off of idle, this PI does not apply.
Recommendation/Instructions:
If the SI diagnostics do not isolate a cause for this concern, perform a cylinder leakage test as outlined in the latest version of 07-06-01-011 and in the "Cylinder Leakage Test" procedure from SI. Please document all leakage rates on the repair order.
If a leaking intake valve is found, replace the cylinder head by following the latest version of 06-06-01-017. This bulletin, which contains all of the part numbers that will be needed. The bulletin also contains a revised replacement procedure that no longer requires removal of the oil pan, front cover, water pump, or crankshaft dampener. The cylinder head listed in 06-06-01-017 will come with the valves already installed and it contains harder intake valve seats to prevent future intake valve leakage. When replacing the cylinder head, 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: 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 the latest version of 02-00-89-002. 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.
