Diagnostic Aids

Perform this test only when directed by QUICK TEST. To prevent replacing good components, be aware following non-EEC areas may be at fault:

Engine base condition (cam timing, valves, rings, etc.).
Brakes.
Transmission fluid, friction elements and cooling.
Transfer case linkage or internal condition.

This test is only intended to diagnose:

Harness circuits LOW/ OCIL and OCS.
Faulty ECA.

Fig 1: Low & Overdrive Cancel Ckts. (Touch Drive Option)

Fig 2: Low & Overdrive Cancel Ckts. (W/O Touch Drive Option)

1) Code 65/632 Or 97/631 Code 65/632 indicates Overdrive Cancel Switch (OCS) is not cycled between engine ID code and WOT check during KOER SELF-TEST . Code 97/631 indicates OCS circuit fault during KOEO SELF-TEST . Possible causes for these faults are:

Faulty OCS switch or switch not cycled.
OCS bulb burned out.
OCS circuit open or grounded.
Faulty ECA.

Perform QUICK TEST . If no codes are present, fault is intermittent and cannot be duplicated at this time. If Code 47/633 or 65/632 is present, go to step 2). If Code 97/631 is present, go to step 3).

2) Overdrive Cancel Switch Turn ignition off. Disconnect 60-pin ECA connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Turn ignition on. To check LOW circuit, measure voltage between test pin No. 12 and test pins No. 40 and 60 at breakout box. To check OCS circuit, measure voltage between test pin No. 41 and test pins No. 40 and 60 at breakout box while cycling overdrive cancel switch. If voltage cycles, replace ECA and repeat QUICK TEST . If voltage does not cycle, go to step 3).

3) Check Circuits For Short To Ground Turn ignition off. Leave ECA disconnected from breakout box. Disconnect switch. To check LOW circuit, measure resistance between test pin No. 12 and test pins No. 40 and 60 at breakout box. To check OCS circuit, measure resistance between test pin No. 41 and pins No. 40 and 60 at breakout box. If resistance is more than 10,000 ohms, go to step 4) (Code 97/631) or step 6) (Code 47/633 or 65/632). If resistance is 10,000 ohms or less, repair short circuit. Repeat QUICK TEST . If code is still present, go to step 5).

4) Check Power Through OCIL Circuit Turn ignition off. Leave ECA disconnected from breakout box. Measure voltage between test pin No. 32 and test pins No. 40 and 60 at breakout box. If voltage is more than 10.5 volts, replace ECA and repeat QUICK TEST . If voltage is 10.5 volts or less, go to step 5).

5) Check Output Driver Voltage Signal Turn ignition off. Leave ECA disconnected from breakout box. Disconnect switch. To check LOW circuit, connect DVOM positive lead on KEY POWER terminal of fuse panel and negative lead on test pin No. 12 at breakout box. See Fig 3 . To check OCS circuit, connect DVOM positive lead on KEY POWER terminal of fuse panel and negative lead on test pin No. 32 at breakout box. If either voltage reading is less than 2 volts, check bulb and fuse. If bulb and fuse are okay, repair open circuit and repeat QUICK TEST . If both voltage readings are 2 volts or more, go to step 6).

Fig 3: Identifying KEY POWER Terminal in Fuse Panel

6) Check Circuit Continuity Turn ignition off. Leave ECA disconnected from breakout box. Disconnect switch. To check 4x4 LOW circuit, connect DVOM positive lead on KEY POWER terminal of fuse panel and negative lead on test pin No. 12 at breakout box. To check OCS circuit, connect DVOM positive lead on KEY POWER terminal of fuse panel and negative lead on power side of OCS wiring harness connector. Connect DVOM positive lead on test pin No. 41 at breakout box and negative lead on power side of OCS wiring harness connector. If either resistance reading is 5 ohms or more, repair open circuit and repeat QUICK TEST . If both resistance readings are less than 5 ohms, go to step 7).

7) Check Circuits For Short To Power Turn ignition off. Leave ECA disconnected from breakout box. Disconnect switch. To check 4x4 LOW circuit, measure resistance between test pin No. 12 and test pins No. 37 and 57 at breakout box. To check OCS circuit, measure resistance between test pin No. 32 and test pins No. 37 and 57 at breakout box. Measure resistance between test pin No. 41 and test pins No. 37 and 57 at breakout box. If resistances are more than 10,000 ohms, replace switch and repeat QUICK TEST . If any resistance is 10,000 ohms or less, repair short circuit and repeat QUICK TEST .