Intermittent Service 4WD Message - keywords actuator B0790 C0306 case indicator lamp light MIL message module NP8 TCCM transfer

This PI was superseded to remove parts restriction. Please discard PIP3737E.

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

Intermittent Service 4WD message comes on in the driver information center. The TCCM may store no codes, may store a B0790 or possibly a C0306 code. Customer may also comment that they are unable to make the T/Case shift into any range or be inoperative. When commanded there will be no audible motor noise coming from the transfer case actuator/encoder motor. Condition may or may not be able to be duplicated.

Check TCCM connections and confirm power and ground to the module. Also check the affected GM LAN communications and select switch circuits as per the applicable service information in eSI for any electrical concerns.

If connections are OK check the TCCM Julian date, if built PRIOR to 2076 (see the image below for identification) suspect a possible TCCM concern. If the TCCM was built AFTER clean date of 2076 follow published diagnosis. For dtc c0306 if published diagnosis does not lead to a root cause suspect a possible transfer case actuator/encoder motor concern. For a no code stored or no communication concern verify the TCCM has the correct and latest calibration and software if OK check voltage, ground and communication circuits prior to TCCM replacement. For dtc b0790 follow published diagnosis.

Several TCCM module manufacturing process improvements have been implemented after Julian date 2076. This is the 205th day of 2006.

The Julian date is included in a series of digits on the module label. Digits 5 through 8 on the label just above the lower bar code will give the Julian date. See the image below.

All current GMSPO inventory on hand was manufactured after this date and contains the latest process improvements.

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.