| Subject: | Engine Rattle or Tick Noise Worse with AFM (Active Fuel Management) Enabled |
| Models: | 2005-2006 Buick Rainier |
| 2005-2006 Chevrolet Trailblazer |
| 2005-2006 Chevrolet Impala, Monte Carlo |
| 2005-2006 Pontiac Grand Prix |
| with 5.3L Engine (RPO LH6 or LS4 Only) |
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
Some customers may notice a light engine tick or rattle noise while driving the vehicle. This noise will be more apparent with AFM enabled (4 Cylinder Mode) and it may be mistaken for a noise in the transmission. This noise may be the result of normal
timing chain slack.
Recommendation/Instructions:
Use a Tech 2 to enable and disable AFM while listening to the front cover area of the engine at a hot idle. If a light tick/rattle noise is heard that increases when AFM is enabled, normal timing chain slack is the root cause of this noise. Only temporary
noise relief will be achieved by replacing the timing chain, crank gear, cam gear, and timing chain dampener. As a result, no repairs are suggested at this time. This is currently considered a noise characteristic of this engine.
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.
