My rear window wiper will not operate (rear washer works fine). I posted about this 6 months ago, but, now, I have had two mechanics (independent and Dodge) both tell me that a) the rear wiper motor is OK, and b) the in-dash switching unit (the little button for rear wiper on) is OK, and, c) that they can provide fused hot-wire power (via the harness at the BCM) and operate the rear wiper motor. They both conclude that it is the BCM and I need to replace it

There is nothing else wrong with the BCM - the codes they get from their DRB III only show that the FCM (front control module) was disconnected at some point in the past, and that this usually means the battery was replaced - which was done last fall. They both say there is NO TEST for the BCM that would show definitely it is failing in its requirement to operate the rear wiper in response to the "on" setting of the indash switch.

I read that this feature of the BCM (rear wiper motor control) is a "LEARNED FUNCTION", whatever that means. Has anyone ever heard of this before? Could it be that this BCM only needs to be "programmed" so as to "learn" how to operate the rear wiper? It goes against my grain to replace the entire BCM for this one little malfunction, since the BCM has many more very important functions which are working just fine right now (you know - if it ain't broke, don't fix it).

Replacing the BCM via the Dodge dealer is just under $400 - going the independent route is around $200.

This malfunction is driving me to my wits end - how could a perfectly fine BCM suddenly "forget" how to operate the rear wiper? Why can't they just reprogram that "learned function" right in the car (without removing the BCM) - that shouldn't take more than a few minutes?

If I go ahead and have the BCM replaced, then I have to worry about all the other functions that are doing fine now, and, I'll never know if maybe the replacement BCM might also have some "learned function" that might start malfunctioning.

It is not knowing how this problem developed in the first place, and, not understanding the need for a total BCM replacement that is driving me nutty.

Any experience with this out there?

 

What year is the van?

 

Nope, never heard of a BCM "learning" anything beyond what it is programed to do. The PCM and TCM learn your driving habits and make adjustments accordingly. Maybe that's where the confusion lies.

Pull the IOD fuse for 2-3 minutes to reset the BCM. If that doesn't wake up the wiper disconnect the negative battery cable for 2-3 minutes. If it still sleeps and a new BCM is causing nightmares consider looking into rewiring the switch or adding a switch to power the wiper motor off the battery bus. Make sure a fuse is included.

 

It is a 2007 Dodge Caravan (4-cyl, no power accessories, no frills).

The service manual says, on page 8E-3 that "The BCM has the ability to LEARN additional features in the vehicle, provided the appropriate switch input and PCI data bus messages are received. Refer to the "LEARNED FEATURES table".

Again on this same page (8E-3), there is the "LEARNED FEATURES" table, and the first feature is "REAR WIPER CONTROL ON HVAC CONTROL ON INSTRUMENT PANEL", where the corresponding key is "PCI BUS MESSAGE RECEIVED FROM HVAC CONTROL".

The service manual makes no mention of how to "TEACH" this, or ANY, feature to the BCM! I don't know what to make of these statements in the service manual - what do we do with it?

On page 8E-4, it says that there are ONLY TWO CODES logged by the BCM for which replacement of the BCM is concluded: #01 - Internal BCM failure, and, #1F - J1850 Internal Hardware Failure.

Since my BCM has not logged either of these codes, I am hesitant to replace the BCM, even though both my independent mechanic and the Dodge mechanic tell me that I should replace the BCM anyway - they cannot explain this passage in the service manual, but, they just say that sometimes the BCM doesn't log an error code but needs replacing anyway.
This is just confusing to me and simply unacceptable as a way to do service business.

Why would Dodge publish a service manual and then instruct its mechanics to disregard it in some cases? Why would Dodge make programming this BCM thingie so secret that even their own mechanics have no idea how to enter any of the "learned" features to get this BCM to take over and operate the rear wiper when it gets the "blip" from the indash "wiper-on" switch? This "blip" was confirmed by my independent mechanic who put it on an osscilloscope and noted this "blip" when he depressed the "wiper-on" switch on the indash instrument panel, but, he said there was no corresponding acknowledgment "blip" from the BCM, which is supposed to happen (he says).

The battery has been disconnected many times during this ordeal, for several minutes each time - no "resetting" of the BCM (as per this feature) occurred at any of these times.

What is the IOD fuse? Is it one of the many fuses located on the IPM (Integrated Power Module - under the hood on the driver's side)? Both mechanics checked ALL the fuses in the IPM and state that they are all good.

What I am hoping for is someone who has had this same problem and what they did to fix it, and, I am also hoping SOMEONE with Dodge will respond as to what gives with this BCM thing that you cannot simply reprogram a failing "learned" feauture without having to pull and replace the whole BCM in the process? They require my OLD BCM as a "core charge", and, the replacement BCM will not be a "FACTORY NEW" BCM, but, a "reprogrammed" one for my vehicle (they need the VIN for my vehicle). That tells me that somewhere (who knows where), Dodge service folks are capable of programming the BCM and they just take in malfunctioning ones and simply reprogram them unless they have blown some internal hardware circuits. So why not allow for this particular feature to be reprogrammed right where it is?????? Why so darn much money to just "reprogram" a BCM that has no hardware failure?

This episode has soured my prior love affair with Dodge/Plymouth/Chrysler - it seems they are just hiding their "secrets" to make more money on expected repairs that cannot be fixed any other way.

My independent mechanic did suggest, off the cuff, that I could put in a fused power toggle switch to operate the rear wiper in continuous mode, but, he agrees this idea would be "tacky". The rear wiper is supposed to operate in intermittent mode, between 4-7 seconds depending on the speed of the vehicle and the BCM is supposed to control this as it gets vehicle speed data from other inputs.

It just rubs me the wrong way to have to replace a BCM that is functioning perfectly in every way except for this lone "learned" feature, and, why Dodge wants so darn much money for their secrets that they won't even let their own mechanics find out about.

 

I was going to ask if fuse 11 was checked. But I guess it was. The next thing I would do is remove the liftgate panel and check for power and ground to the motor. If you have power and ground, the motor maybe no good.

 

My independent mechanic did that (checked the motor with a fused test lead). He did it in the back with the rear panel removed, and, also, he checked it using the BCM harness and shorting out pin 32 with a fused test lead - in both cases the wiper motor spins continuously.
For some reason, the BCM is just not powering up the rear wiper motor and that is where I am stumped.

I was thinking - I never actually operated this rear wiper before. As soon as I got it, I lent it out to someone else (who is no longer available) and so I really don't know if the rear wiper EVER worked. When I got this vehicle back, the rear wiper was not working but I wonder if it EVER worked because I can't see how a BCM "forgets" a "learned" feature!!!!!!!

 

I'm guessing the problem maybe in the front control module or the IPM/TIPM.

 

The diagnosis they gave you sounds a bit odd... It is very hard for a module to fail on its own... Just Like master tech states, the signals have to be tested at the rear hatch... if nothing there the the input command, which is the switch has to be tested for proper operation. With a scan tool, the outputs could be commanded to see if the actual module is working...if the technicians did this test , and got no command signals at the rear wiper module then it could be a wiring problem. Remember there are plenty of tests to be done before condeming a module... can you provide the exact write that the technicians that inspected it wrote on your work orders? If you are mechanically inclined Maybe I can give you some steps to try....

 

I am more than willing to try any test that might shed light upon this, but, I have already paid good money to two mechanics who were supposed to run these tests.

First, the independent mechanic, who comes highly recommended locally and specializes in auto electronics and auto computer codes, performed the wiring test after testing both the indash switch (with an osscilloscope) and the wiper motor. I didn't get to watch (customers are not allowed in the work bay), and he did NOT give me a written report, but, he did talk to me about what he did.

First, he said he provided ground at the rear motor to make sure the motor would spin, which it did. Second, he put a scope between the indash switch and the BCM and noted the required "blip" when depressing the "wiper-on" switch. He also stated that the BCM was *SUPPOSED* to respond with an "acknowledgment" blip, which IT DID NOT DO. He suspected that the BCM simply is not programmed to respond to the indash "wiper-on" switch being depressed. To confirm that there was no wiring problem from the BCM to the rear wiper motor, he disconnected wiring harness C2 from the BCM, and provided solid ground to pin 32 via a fused test lead to the battery. He reported that by merely touching pin 32 with this ground lead, the rear wiper motor would operate (spin). He concluded that there was no wiring problem between the BCM and the rear wiper motor (neither a ground short, nor open circuit). He was convinced that the BCM needed to be replaced because he was not aware of any procedure for programming the BCM, IN PLACE, to respond to the wiper-on signal from the indash switch.

He said there were NO CODES logged by the BCM, but, that he had seen BCM go bad before without logging any codes, and, that replacing them (after eliminating all other options) had fixed the problem.

I paid him his going rate for this diagnosis, and, he awaits my return with instructions to go ahead and order the replacement BCM.


I then went to the Dodge dealer, and paid them to diagnose my BCM and to determine why the rear wiper does not work. Again, I was not able to watch him work in the bay, but had to wait in the waiting room. Even then, I didn't get to talk to the mechanic, but, instead, I had to talk to the "service rep" - a glorified salesman peddling repair work for the mechanics in the back.

This service rep was very UNknowledgeble, and couldn't explain anything to me about the recommendations made on their report. He said that they determined that the motor and switch were fine, and that they needed to check the wiring from the BCM to the rear motor, and, if the wiring had no problems, then, they would conclude that the BCM needed to be replaced.

I explained to him that my independent mechanic had already checked the wiring and determined that there was no problem there, but, the Dodge folks insisted that I come up with and additional $100 for them to determine on their own that the wiring was OK. I balked, of course, and insisted that there must be SOME TEST for the BCM specifically, so that the need to replace it would be based on a clear error code, instead of by the process of elimination. They wouldn't budge, cough up $100, or go away.

So, I am thinking about letting my independent mechanic replace the BCM, but, I am more than willing to check anything that might shed light on it. Remember, I have paid good money to 2 different mechanics to tell me the motor and switch are good, and, to my independent mechanic to tell me that hot-wiring pin 32 of the BCM C2 harness results in the rear motor spinning continuously, so there is no problem with the wiring from the BCM to the rear wiper motor.

I looked over the service manual painstakingly for any pinouts for the FCM and IPM that would refer to the rear wiper motor, but, there are none. I have serious doubts that either the FCM or the IPM have anything to do with the rear wiper motor - unless Dodge just didn't bother documenting it in their service manual.

I am leaning towards suspecting that the BCM was never actually programmed at the factory to respond to the rear wiper motor - somehow maybe it slipped through the crack and I, nor my loanee, never actually engaged it to discover the failure.

Anyway, he scribbled something on the bill which says:

"BCM to motor code"
"FCM not received"
"Hvac communication fault - FCM"

The service rep was truly an ignorant sot, but, he said his mechanic told him these codes indicated that the battery had been disconnected at some time in the past, and, they did NOT indicated anything wrong, other than no battery sometime in the past. I did replace the battery last October.

Let me know what tests you think could help, and what we expect to learn that we don't already know.

 

Dont know what to tell you there, it seems you got incompetent technicians checking it. With the proper tooling and diagnosis tools they can verify that issue and pintpoint in that hour of diagnosis that you paid. But nowadays its very hard to find good technicians specialized in computer diagnosis. The dealer you took the van too should of been able to perform tests with the witech and trace the problem but it seems the tech got lazy in that hour and did not. Let me look at the wiring diagrams for your van and i will get back to you. See if i can lead you in the right direction...