Technical Service Bulletins

GM wet codes

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GM wet codes

A range of GM vehicles may display an illuminated MIL along with several DTCs, resulting from water intrusion into the spark plug recess areas. This involves 2008-2009 Chevy Colorado and Trailblazer, GMC Canyon and Envoy, HUMMER H3 and H3T and Saab 9-7X (all equipped with engine RPOs LLR, LLV and LL8).

The engine may run rough, and DTCs P0300, P0301, P0302, P0303, P0304, P0305 or P0306 may be set or in history.

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

Do not reprogram or replace the ECM for this condition. If evidence of water intrusion in the spark plug recess areas is not observed, refer to the appropriate DTC procedures in the service manual.

  1. Observe the Misfire Current Counters parameter with a scan tool, in order to determine the affected cylinder(s).
  2. Remove the air cleaner resonator and outlet duct.
  3. Disconnect the engine wiring harness electrical connectors from the affected ignition coil(s).
  4. Remove the ignition coil bolt(s) and ignition coil(s) from the camshaft cover. NOTE: 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.

Warning: Wear safety glasses when using compressed air, as flying dirt particles may cause eye injury.

  1. If any water is present, remove the water from the spark plug recess areas with low pressure air.
  2. Remove the affected spark plug(s) from the cylinder head.
  3. Replace ONLY the affected spark plug(s) with new spark plugs as needed.
  4. Fill the bottom of the ignition coil bolt hole vent with Loctite 565 PST Thread Sealant, and apply sealant to the bolt threads.
  5. Replace only the affected ignition coils with new coils as needed.
  6. Connect the engine wiring harness connectors to the coils.
  7. Replace the air cleaner resonator and outlet duct.
  8. Clear all DTCs.


  1. Remove the hood air grille.
  2. Secure 3M Strip Caulk P/N 051135 around the outside perimeter of the integral retention clip openings in the hood (all 4 sides of each rectangular slot).
  3. Install the hood air grille and verify that it fits tightly against the hood.
  4. Advise the HUMMER owner to use care when washing the hood. Extreme water pressure should not be directly applied to the edges of the hood air grille.


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