Your relay sound might be associated with a relay that controls a bunch of dash functions - have a look in the power distribution center. Everything you've described is dash related. If you don't look for an electrical fault, you won't find it & without a wiring diagram to make some sense of what you need to look for, a solution could be a long time coming.

The ABS is not vehicle speed related, it's calculated on wheel speed differences. The ABS light is dash related.

The vehicle engine is running, the vehicle is moving, and its transmission is shifting because all the speed related sensors are working - the PCM can't see the human factors side (dash outputs).

 

You can always try the General Motors approved "tap test". It is exactly what it sounds like. With access to the modules, connectors and harness, start tapping the modules and tugging lightly on harnesses and connectors to see if conditions change.

I've found a lot of issues this way.

Do you have a scan tool? Does it show vehicle speed information when moving?

 

You never mentioned whether your truck leaks around the windshield into the dash area - if it does, this would be the first place I'd look. It doesn't take much water to cause a lot of corrosion in connectors (and even inside wire insulation) to cause a lot of headaches. In earlier vehicles, Chrysler used "flex print" circuit boards in many dash modules - a bit of water would "eat" right through some of the traces on these flex boards making them partially or wholly inoperative. They may still be using similar products.

 

No water leaks that I'm aware of? I should mention this thing's been garaged since new, and has reasonably low mileage (65k). It spent the majority of it's time in Mi. though, and a lot of that time spent on I75 running in the salt from S.E. Mi to the northern lower.

Re: The ABS, according to my reading the last few days, it actually does supply the signal that's sent out via the controller area network (or CAN). This would be the signal the dash uses? The ABS module takes the data from the wheel speed sensors (or vehicle speed sensors, depending on where you're reading) and among other things turns it into serial data for use on the data buss (CAN). At least that's the way I have it interpreted at the moment? Would love to have somebody show me I'm wrong with more useful info.

I was wondering how the trans still seemed to know what to do earlier? Found that answer too. The speed sensors on the side of it supply info for use with the trans only! Not like the days a while back when your speedo cable attached to an adapter located there! So this is all starting to fit.

I've been through all the poking and rattling stages, trust me! As well as pulling, inspecting and reseating connectors.

So here's the latest, where I'm at now.
I used the connector pin out diagrams to locate the 3 sets of speed sensors (Left front, right front, and rear). They end up at the ABS module connector. I dont see them anywhere else? I've used an ohm meter to check each of the pairs and nobody's home on any of them. No continuity. So I pulled the connector at the right front, in the wheel well, to check the sensor itself. I forget the exact reading I got, but suffice it to say, it showed continuity. So I'm puzzled how all 3 of these sensors might have open circuits according to the results of my tests at the ABS module connector?

Completely befuddled now, I sprung for a medium priced OBD-II tester. Its showing 2 errors (P0501 and U1120). Both indicate issues with the speed sensors, but shed very little more light on the issue than what I already know.

My plan is to try and figure out why the speed sensors aren't showing continuity when checked at the ABS module connector. I think if I figure that out, hopefully that will resolve the issue.

Thanks for the input guys. All it's going to take is one idea to get to the bottom of this.... just like your keys are ALWAYS right where you left them, and the last place you look is always where you find it?
-Al

 

Al, you may be onto something. I'm sort of predisposed to making snap judgements & could be wrong when I'm not physically facing the problem & you're obviously doing a lot of "homework". I'll look into this a bit more and see what I can come up with.

I see from various drawings that there are multiple "speed" sensors on the Dakota, but they appear to be for different purposes. The vehicle speed sensor which I believe is in the area of the rear diff should supply the signal that's translated into the speedo speed - I seem to think this is a hall-effect sensor type. The ABS may or may not use this info - I don't see that it needs it. Generally it works on a wheel speed difference and takes it's information from the wheel speed sensors to perform it's "difference" calculation. I see in some pictures that there's a speed sensor coming out of the transmission, but I don't know the use of this yet.

 

Yup, they're so vague about all this it's frustrating as hell. The "vehicle speed sensor" is one and the same as "rear ABS sensor". How and what they use this for varies as there are 2 different ABS systems. I caught and looked into this after noticing 2 totally different ABS module connectors in the "pin out" section of the manual? One is just for the rear ABS system, the other front and rear ABS? The rear only uses what they call a "front" module, and that's not used on the 4 wheel ABS? (I have the 4 wheel ABS). Could they possibly be more vague or confuse this more?

Front trans sensor basically reads "input" rpm, which I'm assuming is the same as engine (?), and the back one measures output shaft rpm. Neither are referred to anywhere as "vehicle speed sensors" like the ABS sensors are. I'm assuming they feed the PCM to allow it to monitor both, then couple that info with a bunch of other stuff, then tell it what gear it should be in as I know it supplies that info.

Also, OBD-II trouble codes I'm getting, P0501 and U1120, both refer to vehicle speed sensors.

Thanks for your time looking into this Alfons! -Al

 

Frustrated, dropped it off at the dealer this afternoon. Will post results...

 

Dealer, after calling and saying they couldn't find anything wrong with it, asked if they could drive it 20 miles to see what it did. With that authorization it started acting up right away. 2 hours of diagnostic time later (!!!) they found a broken wire leading from the ABS module to the Integrated Power Module (fuse box).

Completely relieved as my biggest concern was taking it someplace with a tech that would just keep throwing parts at it until it was fixed....

Many thanks to Crystal Automotive in Homosassa Florida, and Jonathan, the service manger who kept me abreast of every move they made! -Al

 

glad they found the problem. I probably would have replaced all the sensors and then been mad because it wasn't fixed. I also think the dealer deserves a big THANKS for finding the problem.