2006-07 C4500 C5500 Commercial Cutaway Models With 6.6L LLY Diesel Engine Exhibit Speedomoter And Tachometer Gauges Fluctuations For A Few Seconds After Cold Start Up - keywords active air cold heater

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Some 2006-07 C45 C55 Commercial Cutaway Models with 6.6L LLY diesel engine can exhibit speedometer and tachometer gauge needle fluctuation for the first few seconds after a cold start up.

On cold start up the 6.6L diesel engine Air Intake Heater (AIH) is activated and can create an electronic interference signal that will cause the speedometer/tachometer needles to fluctuate for approximately 5 seconds.

To verify this electronic interference condition, with the ignition off, disconnect the Battery + supply in Circuit #19 from the AIH module stud (see Document ID #1658665). Start the engine when cold and if the needle fluctuation is eliminated, follow the repair instructions below.

Note: If the speedometer/tachometer needle fluctuation is NOT eliminated, do not perform the following instructions and call TAC for further diagnostic assistance.

Install a separate, dedicated Battery + voltage supply wire for the AIH module as follows:

1. Fold over the original AIH module wire terminal and tape it to the OEM harness to protect and insulate the terminal end (see Figure #1).
2. Use a length of red 10ga wire long enough to reach from the battery positive terminal to the AIH module stud. Install a 6.0 inch long 14ga fusible link to the battery end of the wire and an eyelet terminal on the opposite end to fit over the AIH module stud.
3. Place the new dedicated wire inside protective plastic wiring conduit. NOTE: do not cover the fusible link wire with the protective conduit.
4. Install the dedicated wire from the Battery + terminal to the AIH module stud and check the routing to prevent contact with other components
5. Perform a cold engine start up and check to see that the speedometer/tachometer needle fluctuation is eliminated and the Air Intake Heater functions properly per Document ID #1639373.

Figure 1

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.