'O5 4x4 Dakota Laramie with 65k on it. Out of the blue (I've done nothing to it other than adding gas and driving it since it was last serviced this past Oct.) I picked up an erratic electrical gremlin that's affecting my speedo, brake, ABS and check engine lights, and my auto door locks! Problems appeared at the same time. Nothing progressive.

Problem starts when the truck is started. After the dash diags are done running after the engine starts, the brake, ABS, and check engine lights remain lit. Drop the truck into gear and proceed down the road, everything seems normal until you notice the speedo is inop.? All other gauges and lights seem to be functioning normally. Engine running smooth, trans shifting normally. No other hint there's trouble anywhere.

Then, you hear the muted click of a relay closing, the warning lights go out, the speedo starts functioning, and the auto door locks engage! This happens on a completely random basis, and nothing else seems to be affected? Everything may stay functional for the balance of the errand, or the cycle may start over again a few minutes later (warning lights on, speedo quits, then back to normal).

So far, I've pulled the battery cable to reset everything, and cleaned the ground strap connections for the PCM. Any other ideas would be most welcome!

TIA, -Al

 

test your battery and charging system

 

I know in my '96 Dodge Dakota the wiring harness in the steering column was bad and if you moved your steering wheel up or down it would cause problems. Dodge didn't do a good job of the way they ran the wiring through the steering wheel. It's like they got it too tight. Mine ended up pulling clean out of the key switch and I had to fix it. But it could also be a loose connection in the plug for your instrument panel too. Someone else will hopefully chime in that has more experience.

 

Also I have noticed that when I get in my truck if my knee hits my steering wheel or gets caught under it and puts pressure on it my ABS light will light up on my instrument panel and i have to bump my steering wheel and turn off my truck then turn it back on to get it to go off.

 

Update...
Battery and charging system are fine. Thanks.

I did run another errand with it, and though the trans is shifting fine, thinking otherwise, it's got no clue it's moving. The cruise is no longer working, and the seat belt chime that goes off almost as soon as you start moving isn't working either?

 

I would start with pulling the shroud from the steering column. Check the service manual for instructions. (sticky on main page)

 

Strange things like this can often be attributed to a bad connection in a circuit - the chances are that it's most likely a bad ground, but corroded contacts or wires can also be on the list - a sticky relay might also be a problem. You mentioned that the problems are rectified when you hear this "muted relay click" - there won't be that many of them that will kick in to do the lamp test on start-up, so I would suggest downloading the service manual from the sticky post and then look up the section that deals with the start-up circuits (chapter 8 is usually all the wiring stuff, so between the index and pawing through chapter 8, you should get the info you're looking for. The box under the hood that contains the relays, should have a descriptive title on what each relay is for - you should also be able to find a picture with similar description in the manual. Find the relay(s) that sound like they'd be involved, then you'll need to get a "known good" relay and replace the one(s) you think might be the problem (one at a time, moving the known good relay from socket to socket until you find the one that's the problem.

 

For the sake of bouncing ideas around, I'm convinced this issue has something to do with speed. Here's why:

The first clue is the Speedometer is inop.

The ABS system (with associated light) depends on speed inputs, and I understand that system feeds the brake light as well (thank you section 8).

The power door locks are set to engage/lock automatically when the truck starts to move (10 mph or something like that). I'm pretty sure there's a relay that's engaged when the speed get to a certain point (the one I'm hearing), much like the alarm/gong telling you your vehicle is in motion and your seat belts aren't fastened (that's not working either)? The key here is that whatever controls this circuit, and controls that power door lock relay, doesn't know the truck is moving. None of that works...

Cruise control, same issue. The dash indicator comes on telling me it has power, but it will not engage. Same story - it doesn't know the truck is moving?

Confusing the the thoughts regarding speed sensing, is the fact the trans is shifting perfectly. What's up with that? Could be it uses a different speed sensor, or, the truck is picking up the info the trans needs to shift correctly, but due to a bad connection and/or short, it's not passing the info along to the other systems?

All systems that depend on speed information, other than the trans, seem to be completely down.

Alfons, agreed. The answer is in section 8. The problem is section 8 is huge AND so technical it will make your eyes bleed inside half an hour.... That's why I'm here, hoping somebody has dealt with this or a similar issue recently enough to remember some details.

Thanks guys, -Al

BTW, It's no longer erratic. It's a full time thing now.

 

Do you have turn signals and headlights? Doesn't the FCM control all that you have described as well as the lights? I cant remember exactly... but that could be your culprit. I thought we've had others with a similar issue.

 

Pretty sure all this is Power Control Module (PCM) related? All speed functions/speed controlled functions, including odometer, are now down. Lights are fine and all other functions seem to be up and running as well.

Nothing seems to know the truck is moving! How is it that the tranny is still shifting fine (thank God!)?

PCM ground strap removed and cleaned (both ends), transmission speed sensor connectors (both of them) have been removed and checked for corrosion (spotless, no hint of contamination!) as well as the 4 big connections that plug into the PCM (also spotless). No joy....

-Al