Colorado 2WD L5-3.5L VIN 6 (2005)
Spark Plug: Technical Service Bulletins
Engine Controls - DTC P0300 Diagnostic Aid
Bulletin No.: 07-06-01-011A
Date: August 07, 2007
INFORMATION
Subject:
Diagnostic Tips for DTC P0300 Engine Misfire Detected and Cylinder Leakage Testing
Models:
2004-2006 Chevrolet Colorado
2004-2006 GMC Canyon
2006 HUMMER H3
with Vortec(TM) 2.8L I-4 or 3.5L I-5 Engine (VINs 8, 6 - RPOs LK5, L52)
Supercede:
This bulletin is being revised to include 2.8L LK5 engine. Please discard Corporate Bulletin Number 07-06-01-011 (Section 06 - Engine/Propulsion
System).
The purpose of this bulletin is to provide technicians with diagnostic tips for DTC P0300 and cylinder leakage testing.
Diagnostic Tips for DTC P0300
If DTC P0300 sets, follow DTC P0300 diagnostics in SI. The following tips may also be helpful:
Isolate the cylinder or cylinders responsible for the P0300 misfire code and determine if the misfire can be moved to another cylinder by swapping
components such as spark plugs, ignition coils and fuel injectors.
If misfire is random, diagnose for possible mechanical noise that may be misinterpreted as a misfire.
If diagnostics lead to suspect cylinder head valve seats, conduct a cylinder leakage test utilizing a cylinder leakage tester following the manufacturer
instructions and Cylinder Leakage Test procedure in SI.
Diagnostic Tips for Cylinder Leakage Test
When performing a cylinder leakage test, the following tips may be helpful:
Carefully follow the manufacturer's instructions for J 35667-A Cylinder Head Leakdown Tester (or equivalent automotive cylinder leakage tester) and
Cylinder Leakage Test procedure in SI.
The cylinder must be at TDC on the compression stroke when testing to ensure that all the valves are fully closed.
If holding the crankshaft balancer bolt with a wrench, regulate shop air to the J 35667-A to 345-414 kPa (50-60 psi) to reduce torque on the crankshaft
balancer bolt when air is applied. For other equivalent cylinder head leakdown testers, refer to the manufacturers instructions.
An alternative to holding the crankshaft balancer bolt with a wrench would be to use the EN-46547 Flywheel Holding Tool. A breaker bar with socket is
another alternative.
If intake valve seat leakage (rare) is suspected, verify by listening for air leakage inside the intake runner.
If excessive cylinder leakage is NOT observed, the cause of the misfire condition is NOT engine mechanical related. Misfire diagnosis should focus on
fuel and electrical for cases where excessive leakage is not observed.
The majority of vehicles will not experience an intake valve seat erosion condition. Expect a variation between cylinders if valve seat erosion has
occurred.
Use the labor code and time provided in the Warranty Information section of this bulletin to receive credit for performing cylinder leakage diagnostics.
Warranty Information
Cylinder leakage test results must be documented on the repair order.
