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Old 08-18-2012, 01:44 PM   #15
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When I was service manager for a Honda dealer in SoCal we had a car that kept blowing the multiplex out. About 3 MP's later, found the car had been in an accident and the ground wire connection behind the front fender was making a poor contact. The grounding connection was painted which did not allow for a complete circuit. The ground back fed through the MP searching for a good ground and kept burning it out.

It was a 2006 Honda Accord with no hitch or add on wiring harness.

This problem was intermittent and very difficult to repair. When we put the new MP in, all systems seemed to work fine. That is until a few weeks later when the vehicle returned with the same concern.

Hope this helps
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Old 08-19-2012, 07:25 AM   #16
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Quote:
Originally Posted by Wanabee FTer View Post
the car had been in an accident and the ground wire connection behind the front fender was making a poor contact. . . The ground back fed through the MP searching for a good ground and kept burning it out.
This sounds a lot like our situation. We haven't had an accident, but we do have the tow equipment with ground connections which might have developed problems. This certainly gives me a plan, check out all the added wiring and make sure the grounds are good.

Quote:
This problem was intermittent and very difficult to repair. When we put the new MP in, all systems seemed to work fine. That is until a few weeks later when the vehicle returned with the same concern.

Hope this helps
You may have helped a lot. Since I first posted, we find that the problem is intermittant. From time to time the the shift lever works normally and comes out of park without special procedures. That suggests to this amateur that the multiplex unit is not actually destroyed.

Could it be the MPs have been ok, but a short somewhere causes the malfunction?

Maybe we might not have to actually replace it? I guess we'd know if I work on all grounds and it starts to function normally.

The fact that the malfunctioning started 2 or 3 weeks after we unhitched and parked the RV and is intermittent even though it has not been hitched or towed in weeks suggests the problem is in the Element itself, not in the RV. Does that make sense?

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Old 08-19-2012, 07:33 AM   #17
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Maybe you should call American Honda, Customer Relations 800 number from your manual.
Sounds like you are a reasonable person. So the caveat "Be Nice" isn't necessary.
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Old 08-19-2012, 12:09 PM   #18
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Quote:
Originally Posted by JucenBrudi View Post

You may have helped a lot. Since I first posted, we find that the problem is intermittant. From time to time the the shift lever works normally and comes out of park without special procedures. That suggests to this amateur that the multiplex unit is not actually destroyed.

Could it be the MPs have been ok, but a short somewhere causes the malfunction?
ON the Accord we worked on, the main problem was the power door locks stopped functioning. There was also some other minor things that did not work, just don't remember what all they were.

When we worked on cars with intermittent shift interlock failure, 90% of the time we found a faulty brake light switch. Best way to check is to catch it when the gear shift lever will not come out of park, leave your foot on the brake pedal and have someone else get outside of the car to see if the brake lights are on. If brake lights are off, chances are you have an intermittent failure of the brake light switch.
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Old 08-20-2012, 07:45 AM   #19
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When we worked on cars with intermittent shift interlock failure, 90% of the time we found a faulty brake light switch. Best way to check is to catch it when the gear shift lever will not come out of park, leave your foot on the brake pedal and have someone else get outside of the car to see if the brake lights are on. If brake lights are off, chances are you have an intermittent failure of the brake light switch.
Good morning John and group,

We did this test the first time and this time, but we'll repeat. Your information suggests the multiplex problem might be related to another problem we've had with the tow brake system. We use a Unified Tow Brake and have been happy with it. After 2 or 3 years and 20k miles, it started something odd, a beeping warning signal from the controller at the dash in the RV. This would happen after we'd driven about 100 miles and we hit the brakes. It would stop after a short time for no obvious reason. It was suggested that a bad ground somewhere was causing it, but inspection seemed to indicate the grounds were good so we lived with it.

Some time later, I don't even remember how it happened, I discovered that when the beeping was occurring, the Element brake pedal was slightly depressed, perhaps 3/8 inch. Simply lifting the pedal stopped the beeping. I "cured" the problem by installing a bungee cord to provide a very gentle pull on the pedal. No more problem since in 4000 miles plus.

That leads to trhee questions:

1st, could it be that the pedal not returning fully left it riding on the brake light switch and perhaps keeping a voltage on the multiplex unit and burning it out?

2nd: what could be the reason for the pedal return problem?

3rd. How easy is it to replace the brake light switch? Maybe a preemptive replacement is in order.

Bruce
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Old 08-20-2012, 11:48 AM   #20
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Quote:
Originally Posted by JucenBrudi View Post

That leads to trhee questions:

1st, could it be that the pedal not returning fully left it riding on the brake light switch and perhaps keeping a voltage on the multiplex unit and burning it out?

2nd: what could be the reason for the pedal return problem?

3rd. How easy is it to replace the brake light switch? Maybe a preemptive replacement is in order.

Bruce
It's not likely that the brake light switch is causing the MP to fail. It is a simple on/off switch that controls the brake lights and the park interlock system.

I have not seen a problem with brake pedal return in any late model Honda's. Maybe the switch is hanging up the proper operation of the pedal. Is this a problem while driving the toad or only when hooked up?

The brake light switch is located under the dash and is activated by the brake pedal lever. A Honda technician will charge .5 to 1.0 hrs labor to replace it. If you have mechanical skills you can do it yourself.

After rereading this thread, I did not see what your original concern was for replacing the MP. Was it just the park interlock problem and/or RV warning signal?
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Old 08-20-2012, 11:48 AM   #21
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Multiplex

I'm thinking that the multiplex is always on no matter what else is off in the car. If you can identify the fuse(s) that powers the multiplex you might want pull the fuse(s) whenever you tow. If someone (or something) riding the brakes burned out multiplexes like this we would have heard about it in the Element Owners Club. Honda Element Owners Club Forum

- OR -
  • You might be dealing with a bad ground in your brake system.
  • A bad ground for to multiplex as has already been suggested.
  • A bad diode that's feeding RV power back into your Honda's system and toasting the multiplex over time.
  • Or it was mis-wired from the git-go.
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Old 08-22-2012, 03:29 PM   #22
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I have not seen a problem with brake pedal return in any late model Honda's. Maybe the switch is hanging up the proper operation of the pedal. Is this a problem while driving the toad or only when hooked up?
The only time we've noticed the pedal return problem is when towing and we are getting the signal from the Unified Tow Brake controller in the coach. Even when the problem is occurring the pedal has returned almost the full distance so you cannot see the effect. Of course, with the bungee cord in place pulling the pedal into place, the problem hasn't happened again.

Recently, I tried to duplicate the pedal return problem with the Element not hitched. I couldn't do it. It always returned fully whether I pushed it down by hand or had the tow brake pull it down via the brake away switch. My next test of this will be to connected the RV and Element as if for towing and trigger the brake from the tow brake controller in the coach. I can't do that test until the weekend because it requires moving the RV, etc. etc. (long story).

Quote:
The brake light switch is located under the dash and is activated by the brake pedal lever. A Honda technician will charge .5 to 1.0 hrs labor to replace it. If you have mechanical skills you can do it yourself.
I've managed to get in there and inspect the switch for myself. I see that the action is that when the pedal is pushed it releases the switch, it doesn't push the switch. That is relevant because it suggests the possibility that when the pedal fails to return the last 1/4 to 3/8 inch it is partially depressing the switch. Still, the bungee cord fix was in place before both the first and the second park interlock system failures, suggesting this particular tow problem has nothing to do with the park interlock problem.


Quote:
After rereading this thread, I did not see what your original concern was for replacing the MP. Was it just the park interlock problem and/or RV warning signal?
It was the park interlock problem. The RV towing system got brought into the conversation as a possible source of electrical problems bearing on the multiplex burns. Incidentally, the park interlock system has continued to work normally the past several starts, even though we have put off replacing the supposed defective multiplex unit until we think we have the problem fixed.

Bruce
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Old 08-22-2012, 04:02 PM   #23
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I'm thinking that the multiplex is always on no matter what else is off in the car. If you can identify the fuse(s) that powers the multiplex you might want pull the fuse(s) whenever you tow.
Honda's instructions for towing including pulling one of the fuses and we always do. It might not be the one you suggest, but it would be a good guess.

Quote:
If someone (or something) riding the brakes burned out multiplexes like this we would have heard about it in the Element Owners Club. Honda Element Owners Club Forum
That makes sense.

Quote:
- OR -
  • You might be dealing with a bad ground in your brake system.
  • A bad ground for to multiplex as has already been suggested.
  • A bad diode that's feeding RV power back into your Honda's system and toasting the multiplex over time.
  • Or it was mis-wired from the git-go.
good suggestions. I'm running them down. I checked the grounds which are part of the Element side of the Unified Tow Brake system. They are physically sturdy and appear to be electically fine. This is what I did: I took my VOM and read voltages between the positive terminal and negative terminals on the battery as a base reading. Then I moved the ground probe along the paths to the several grounds. All readings were identical out in the hundredths of a volt.

I don't know how to test the ground to the multiplex, but I should get an idea from the wiring diagrams.

As for a bad diode, I don't know where that diode might be or how to test it. I didn't do the original installation but might have the instructions on file.

As for miswired originally, I am tentatively ruling that out because we had towed 20k with the Unified Tow Brake before the first burn out and probably more than 60k with the Brake Pro before that, all with no problems like these.

Bruce
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Old 08-22-2012, 05:05 PM   #24
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Quote:
Originally Posted by JucenBrudi View Post
It was the park interlock problem. The RV towing system got brought into the conversation as a possible source of electrical problems bearing on the multiplex burns. Incidentally, the park interlock system has continued to work normally the past several starts, even though we have put off replacing the supposed defective multiplex unit until we think we have the problem fixed.

Bruce
I am not convinced you have a faulty MP. Additional problems besides the park interlock intermittent failure would be present.

The problem must be duplicated to be able to properly diagnose a faulty circuit. Otherwise you will be looking for a needle in a haystack. Yes you could inspect the grounds for the park interlock system, but you will need a Honda Element electrical (wiring schematic) manual to do this. I still suspect an intermittent brake light switch failure.

Hint, Brake light switch failures can sometimes be temperature sensitive.
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Old 08-22-2012, 09:14 PM   #25
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There is nothing very magical about a multiplex power controller. It is merely a set of relays, one per fused circuit. It distributes power by switching the circuits on/off in response to remote switches that are digital in nature. For example, when you push a button to lock the doors, the button isn't wired direct to the lock solenoid. Instead, the switch is wired to the multiplex controller and sends a signal that says "turn on the lock solenoid" and the controller switches power to do that.

The use of multiplex wiring systems saves a lot of wiring and reduces the size of the wire being used in the vehicle as well. All my motorhome wiring is handled this very same way.

I suspect the problem here is that power is being applied on a wire that is in fact intended to be only a signalling wire. Putting +12v on a wire that is suposed to be only a low voltage, low amp signal line would very likely overwhelm the sensitive signal processing side of the multiplex controller. The problem may be as simple as needing some diodes to prevent backfeed into the controller signal circuits, or as hard as requiring that the wiring to the towing lights be ripped out and re-done by someone who better understands modern vehicle electrical systems.
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Old 08-22-2012, 11:24 PM   #26
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Well Said!

I suspect the problem here is that power is being applied on a wire that is in fact intended to be only a signalling wire. Putting +12v on a wire that is suposed to be only a low voltage, low amp signal line would very likely overwhelm the sensitive signal processing side of the multiplex controller.

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Old 09-03-2012, 08:12 PM   #27
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Update

Hi gang,

A lot has been going on around here and Iíve gotten behind on my updates. The problem with the Element suddenly stopped and hasnít recurred for the past 18 days and we drive that car most days. So the Honda problem dropped from first place and some long-term RV problems moved to first place.

I really havenít done anything with the Element that seems likely to explain the ďcure.Ē I got down at the brake pedal and studied the switch mechanism. In the process I worked the switch several times. Thatís about all Iíve done except check some of the wiring which all looks good.

Iíll keep the thread up to date, but I expect to be involved with the RV problems again in a few days when a new part comes in.

Bruce
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