Technical Service Bulletins

Smoothing out rough-running GMC vehicles

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Smoothing out rough-running GMC vehicles

This TSB applies to 2008-2009 Chevrolet Colorado and Trailblazer, GMC Canyon and Envoy, Hummer H3 and H3T and Saab 9-7X, all equipped with engine LLR, LLV and LL8.

Customers may complain about the MIL on and a rough-running engine. DTCs may include P0300, P0301, P0302, P0304, P0305 or P0306. Upon further examination, the technician may find evidence of water intrusion into the spark plug recess areas.

This condition may be caused by an engine being exposed to a large quantity of water, which may result in some water seeping down past the vented threads of an ignition coil bolt, then flowing through the vent opening that is located in the bottom of the related ignition coil bolt hole and collecting in the spark plug recess.

Observe the misfire current counters parameter with a scan tool in order to determine the affected cylinder(s).

Remove the air cleaner resonator and outlet duct.

Disconnect the engine wiring harness electrical connectors from the affected ignition coil(s).

Remove the ignition coil bolt(s) from the camshaft cover. If water is observed in any of the spark plug recess areas, it will be necessary to apply Loctite 565 PST Thread Sealant to all of the ignition coil bolt hole vents and bolt threads.

Inspect for water intrusion in the spark plug recess areas.

If any water is present, remove the water from the spark plug recess areas using low-pressure compressed air.  NOTE: Wear safety glasses when using compressed air.

Remove the affected spark plug(s) from the cylinder head.

Replace only the affected spark plug(s) with new spark plug(s) as needed.


 Fill the bottom of the ignition coil bolt hole vent with Loctite 565 PST Thread Sealant, and apply the sealant to the ignition coil bolt threads.

Replace only the affected ignition coil(s) with new ignition coil(s) as needed.

Connect the engine harness electrical connectors to the ignition coil(s).

Replace the air cleaner resonator and outlet duct.

Clear the DTCs with a scan tool.


In order to eliminate possible water intrusion on Hummer vehicles, remove the hood air grille.

Secure 3M Strip Calk P/N 051135 around the outside perimeter of the integral retention clip opening (1) in the vehicle hood (all 4 sides of the rectangular slot).

Install the hood grille and verify that it fits tightly against the hood. Advise the customer to use care when washing the hood, as extreme water pressure should not be applied directly to the edges of the hood air grille.


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