A damp day electrical problem

Question:

I have a garaged 1998 Dodge Dakota 1/2-ton, 4wd, 3.9-L V-6 automatic transmission pickup truck with 51,000 miles and it has an electrical problem I cannot solve. When it’s rainy or excessively damp outside my check engine light will come on and I am told it registers trouble code 37, which indicates that the solenoid inside the transmission should be checked.

Upon initial onset of the light, the truck starts out in 2nd gear. After three or four stops and starts the transmission will shift properly, but the light still stays on until conditions become dryer and then the light eventually goes out.

I have tried cleaning all of the wire connections going to the transmission and all grounds I could locate. I have pulled and re-inserted the power control modules to see if any invisible corrosion might rub off the contacts but none of these actions has helped.

The dealer wants $400-plus to rework the transmission and doesn’t seem concerned that the problem only happens in damp weather. Are there any other actions I can take or are there other things to look for?

Answer:

The first thing I would try if I had your situation would be to seal the transmission harness connector and all related wiring against water infiltration. There are a number of ways to do this.

For starters, you can apply a protective dielectric grease compound to the connector’s prongs and receptacles. Dow Corning DC4 and Permatex Dielectric Tune-Up Grease are two examples and there are numerous others on the market. Many automotive parts suppliers and electrical component sellers stock dielectric grease.

After applying dielectric grease to the inner workings of the connectors you can further protect them by encasing the outer areas with excellent quality electrical tape or, better yet, heat shrink tubing.

If the problem persists, there may be damage to the transmission’s control computer. Some have reported that a defective O2 sensor caused permanent damage to those areas of the TCM/PCM that control transmission shifting, with the result being inconsistent shifting, surging, and slamming into gear instead of shifting smoothly. The solution was to replace the O2 sensor and control module at the same time.