Issues with my 3500 van.

[celticwarlock]

I'm not sure where to post this, so I'm putting it here. I have a 2000 3500 series van with about 330,000 miles on it which I'll be to putting into semi-retirement over the next few months, but there's an annoying issue I'm trying to solve.

I had an incident on the road recently which forced me to slam on my brakes. A couple of wheels partially locked up, and a minute or two after I began driving again, the ABS and BRAKE warning lights came on (the van is equipped with rear wheel ABS only). I have had no luck clearing the code from the ABS unit (assuming it stores related codes) by disconnecting the battery. I know that some codes remain for a while and eventually disappear if the fault is no longer detected for a certain number of consecutive start cycles, but that's probably not the case here. This was 3 weeks ago, and the van (which I use daily for work) has been shut down and re-started a great many times since then. If it sits for a day or two and I start it, the lights will go out for about 20 seconds or so, then reappear. I hooked up a scan tool that reads ABS faults and it indicated that it couldn't link with the ABS module, so I got no new information from it. A wiring or sensor failure is very unlikely because the system checks itself at each start-up, and there were no detected issues before stomping on my brakes that one time.

That leads me to the most important question: How can I tell if the module is bad? I *hate* throwing parts at a problem, especially one like this. I'd like to know for sure whether or not it failed before getting another one. Is it common for them to fail 'under load', so to speak? I know all this does is disable the ABS feature and won't cause any other problems, but everything else on the van works, and I'll repair this if I'm able to find out what's wrong.

 

[CBODY67]

I'd suspect a sensor issue, but no knowledge of why one panic stop would trigger any codes. You might need a Chrysler-specific scanner rather than one that's more "generic" or "many brands" in orientation. Back then, it usually took Chrysler-specific scan tools in some areas.

I suspect there should be some way to check the motor/module for correct operation. Have you checked the lines for brake fluid leaks/seeps?

IF the ABS did cycle in that panic stop, you would have known it by the specific noise the ABS motor makes and possibly a "feel" in the brake pedal. That might be the main issue, it didn't cycle but the system still operates normally otherwise?

This might be one issue that might best be addressed with a dealership's service department?

OR, just replace the parts and see if that fixes things. One sensor, on the rear differential housing? The modulator/valve/motor items that make it all work. Not nearly as complicated as more modern systems, as I recall. Have a factory manual available before doing any work on it yourself, though.

ABS modulation systems can be affected by the same issues as brake wheel cylinders getting pitted over time. Which is one reason to flush the system every so often.

Just some thoughts,
CBODY67

 

[67Monaco]

Check the brake fluid level. Just went through this on my '03 Ram. Fluid was low. Only to find a pin hole leak in the line.

 

[celticwarlock]

I have no leaks that I'm aware of, and in any case, the fluid level is not below the critical point where the light would come on. The wheel cylinders were also checked recently when I last had the drums off for an unrelated issue.

I strongly doubt it's the sensor in the differential because the system checks it at each start-up. I don't think it would fail suddenly because of a panic stop.

What I find most puzzling is why the scan tool couldn't communicate with the ABS system. I know certain systems require proprietary software, but the van is an older one, and the scan tool was quite new. It's possible it couldn't access the system, but I have not heard of others having a similar issue when attempting a scan on a Dodge, so I can't be sure what it means.

 

[Davea Lux]

I have no leaks that I'm aware of, and in any case, the fluid level is not below the critical point where the light would come on. The wheel cylinders were also checked recently when I last had the drums off for an unrelated issue.

I strongly doubt it's the sensor in the differential because the system checks it at each start-up. I don't think it would fail suddenly because of a panic stop.

What I find most puzzling is why the scan tool couldn't communicate with the ABS system. I know certain systems require proprietary software, but the van is an older one, and the scan tool was quite new. It's possible it couldn't access the system, but I have not heard of others having a similar issue when attempting a scan on a Dodge, so I can't be sure what it means.

If one or the other of the rear brakes is way out of adjustment, that can trigger a sensor glitch because the system can not compensate for a brake that does not properly apply. You might have a seized adjuster or broken adjuster spring. Check these items first before replacing any other parts.

Dave

 

[jct]

Unplug the abs bulb

 

[celticwarlock]

Unplug the abs bulb

I try not to do things like that, but it's an option, I suppose. Definitely a very last resort, though.

 

[celticwarlock]

If one or the other of the rear brakes is way out of adjustment, that can trigger a sensor glitch because the system can not compensate for a brake that does not properly apply. You might have a seized adjuster or broken adjuster spring. Check these items first before replacing any other parts.

Dave

When I was inside the drums a couple of months ago, I was servicing those very mechanisms. Everything is fine in there, but if I have to, I'll check them yet again.

 

[70NEWYORKER]

Check for power and ground at the ABS module. Check all fuses for ABS (blown or poor contact in box). Get service manual and follow trouble trees for Loss of Comm with module.

 

[CBODY67]

Unless the newer scan tool specifically says it will work on your particular model year and model of Chrysler-built vehicle, it probably won't. Which could well explain the warning light issue. It was a different world back then, with EACH OEM having their own scan tools and such . . . which is why OBD II standardized trouble codes between the OEMs. Find a service manual and/or a Chrysler MasterTech tech training course online (www.mymopar.com or www.imperialclub.org, for example) to learn how the system works and how it does things.

I'll concur that one hard stop should not have caused the issues you are experiencing. It could be that some malfunctions exist and that just caused them to be known? If the "start" self-check turns the warning lights on, then you need to find a scan tool that'll communicate with the system, one way or another. For the ECM, it usually took about 50+ start cycles to clear a "soft" code from that module.

AND, it might be that with a particular sequence of things, the BRAKE warning light might flash in sequence. A standardized sequence, then the trouble code, cycle repeat.

CBODY67

 

[celticwarlock]

Unless the newer scan tool specifically says it will work on your particular model year and model of Chrysler-built vehicle, it probably won't. Which could well explain the warning light issue. It was a different world back then, with EACH OEM having their own scan tools and such . . . which is why OBD II standardized trouble codes between the OEMs. Find a service manual and/or a Chrysler MasterTech tech training course online (www.mymopar.com or www.imperialclub.org, for example) to learn how the system works and how it does things.

I'll concur that one hard stop should not have caused the issues you are experiencing. It could be that some malfunctions exist and that just caused them to be known? If the "start" self-check turns the warning lights on, then you need to find a scan tool that'll communicate with the system, one way or another. For the ECM, it usually took about 50+ start cycles to clear a "soft" code from that module.

AND, it might be that with a particular sequence of things, the BRAKE warning light might flash in sequence. A standardized sequence, then the trouble code, cycle repeat.

CBODY67

This is an OBD II vehicle, of course, and it was scanned using a tool that listed my model amongst those it could communicate with. I made the selection from the menu, and when it attempted to connect to my module, it failed.

I removed the fuse for the ABS and drove the van. The "BRAKE" light went out, the "ABS" light remained on, and my speedometer stopped working. This tells me that the tone ring in the differential is responsible for creating the signal for the speedometer, which also means the sensor on top of the differential housing is working. I put the fuse back in, and things went back to the way they were (BRAKE and ABS light both on, speedometer working again). It seems the wiring to the sensor, the sensor itself, and all wiring responsible for transmitting that data to the computer is working fine. That likely means that the module itself, and anything immediately related to it, might well be suspect. I just need a way of testing it so I'm not throwing parts at the problem.

 

[celticwarlock]

I just ordered another module. I'll post what happens here after the installation is complete (probably in a week or two). Maybe it will help someone who runs into a similar problem in the future.