Transfer Case - Four Wheel Drive Inoperative

File In Section: 7 Transmission

Bulletin No.: 76-74-02

Date: September, 1998

Subject:
Four Wheel Drive Inoperative
(Replace Transfer Case Synchronizer Relay/Install Diode)

Models:
1988-98 Chevrolet and GMC K3 Models with Electronic Front Axle Actuator

Condition

Some owners may comment that four wheel drive does not engage after installation of the updated four wheel drive fast actuator.

Cause

When the transfer case is shifted into four wheel drive, then shifted back to two wheel drive before the axle engages, approximately 7 seconds, a voltage spike may result in failure of the transfer case synchronizer relay.

Correction

Replace the transfer case shift synchronizer relay and install a diode to protect the circuit. Use the part numbers listed below. Use the following Service Procedure.

Service Procedure

1. Install the diode on the relay branch approximately 50 mm (2 in.) from the base of the relay connector.

2. Place CKT 150 (BLK) lead to the "X" (anode) cavity of the diode. Place CKT 1297 (RED) lead to the "Y" (cathode) cavity of the diode. "X" and "Y" sides of the diode are labeled on the case. Do NOT cross the positions of the circuits in the diode.

3. Tape wire leads to the tabs provided on the diode. Then tape over the diode and leads on the relay branch.

Part Information

P/N Description Qty

12110147 Diode 1
12182085 Relay, Synchronizer Shift 1

Parts are currently available from GMSPO.

Warranty Information

For vehicles repaired under warranty, use:

Labor Operation Labor Time

K4125 0.2 hr.