Front Drive Axle Engagement
87chevy29 TSB # DCS1897Date: 03-30-88
BULLETIN ID: 869701 REQUESTING DIVISION: GM TRUCK AND BUS FRONT DRIVE AXLE ENGAGEMENT
1988 K-1, 2, 3 SIERRA TRUCKS
THIS IS A GMC TRUCK DCS MESSAGE
Some comments have been received regarding front axle thermal actuator switches being replaced in service. Dealers should pass on the following message to their sales and service managers.
Sales Manager
When sales people are advising purchasers of 1988 K model Sierras on how to operate the 4WD system, they should instruct them to refrain from making hard turns when shifting into 4WD until after the 4WD indicator light has confirmed engagement.
Service Manager
When diagnosing customer comments regarding 4Wd engagement on 1988 K model Sierras, refer to GMC Truck Electrical Troubleshooting Manual X-8742, page 38-0.
If diagnosis indicates that replacement of the front axle (thermal actuator) switch P/N 15569735 is required, repairs should be made in the normal manner.
When returning the repaired vehicle to the customer, he/she should be advised to refrain from making hard turns while shifting into 4Wd until after the 4WD indicator light confirms engagement. Attempts to shift into 4WD during hard turns could render the thermal actuator switch inoperative, which will result in the vehicle remaining in 4WD.