DTC 29

Fig. 22 Transmission wiring circuit. 1984:

Fig. 23 Transmission wiring circuit. 1985:

If this code is not displayed during the third pass of diagnostic codes, the problem is an intermittent failure. To help isolate the problem, disconnect transmission connector and observe fourth gear status light. Light should be illuminated with circuit open. Manipulate related wiring while observing fourth gear status light. If failure is induced, light will go out. A Code 29 can also be set if the drive ADL switch is misadjusted.
The ECM supplies a 12 volt signal on circuit 438 to transmission fourth gear switch. The fourth gear switch pulls this circuit to ground when transmission is in any mode except fourth gear. Fourth gear oil pressure causes ECM to sense operation when switch opens. Code 29 indicates that ECM is sensing circuit 438 grounded when transmission should be in fourth gear (above 50 mph with throttle switch closed). Possible causes of this condition are:
a. Defective fourth gear switch.
b. Defective wiring or electrical connectors.
c. ECM not able to process signals properly.
1. Disconnect transmission electrical connector.
2. Turn ignition on and enter diagnostics. Observe ``4th gear'' status light above ``Hi'' button on EEC control panel. If light illuminates, proceed to step 3. If light remains off, check circuit 438 for a short to ground. If circuit is satisfactory, check for faulty ECM or ECM connector and repair or replace as necessary.
3. Reconnect transmission electrical connector, then road test vehicle to verify 4th gear operation. If 4th gear operates properly, proceed to step 4. If there is no 4th gear operation, the system is satisfactory and the transmission is at fault.
4. While operating vehicle in 4th gear, enter diagnostics and observe ``4th gear'' status light. If light remains off, proceed to step 5. If light goes on, there is no malfunction in the system at this time and problem is intermittent.
5. Remove transmission oil pan, then disconnect 4th gear pressure switch electrical connector. Turn ignition on, enter diagnostics and observe ``4th gear'' status light. If light remains off, repair short to ground in wire between transmission connector and 4th gear pressure switch. If light goes on, check for fault in pressure switch or pressure switch connector and repair or replace as necessary.