[rt7085]

Over the past months I have been experiencing some intermittent instrument cluster (IPC) issues. Especially after or during humid weather, my instrument starts to show erratic behavior. See the video below. Additionally, when the IPC goes ‘wild’ the tailgate lock is clicking erratically and/or the tailgate wiper blade rotates in a pulsating manner. Of course, the IPC sounds the unlock alarm when all of this happens. The driving performance of the car is not affected, but it is certainly annoying and distracting. I like to observe issues for a while before I fix them; it usually works out better that way. I discovered in the process that the IPC behavior starts when I depress the brake pedal. And when it got dark outside I also noticed that my tailgate lights, mostly the right side, started dimming when the IPC goes crazy. This was an indication that I had power distribution issues or ground termination issues. Finally, another observation was that when I scan the car with ISTA+, I get a rash of KCAN bus related errors for a lot of different ECU’s, indicating bus integrity related problems (as not all ECU’s break at the same time). This all might appear a confusing set of many different issues, but it all boils down to two intertwined simple problems.

Video of the IPC cluster issues:
https://vimeo.com/305337403

Subtle note: Observe that a dot appears between the odometer reading and the mileage counter after a bit. This is an indication the IPC reset and/or there are KCAN bus issues. (Does anybody know for sure; I could not find any reference to this in BMW TIS).

Searching the forums for this issue, I did find some hints. There were some reports about a malfunctioning TPMS ECU. These issues were eliminated when the TPMS module was replaced. The module is around $325 and when you go to the Stealer, add a couple hundred of dollars more. Not a go for me, as the TPMS does work properly when the IPC is not intermittent, indicating a good functioning module. So, I decided to inspect the module.

Picture of the location of the TPMS ECU in the E91 wagon:


Picture of the ISTA+ KCAN bus errors:


TPMS ECU removed:


It should be noted that on the surface there are no visible issues with the TPMS harness, connector and module. But a closer inspection yield this:

Severely corroded TPMS module connector:


It should be noted that one of the pins is broken off. This turns out to be one of the KCAN pins to boot. See the 2nd pin from the left on the top row in the picture (hard to see). Interestingly enough, the module installed next to the TPMS module (PDC: park distance controller) did not have this corrosion. It could be a connector pin plating quality issues with the TPMS module.


The module looks fine on the inside. The module is easy to open and inspect by unclipping the plastic cover in the back.




The missing pin was of course stuck in the harness part of the connector.

Slide the terminal block of the connector sideways out of the connector housing. There are two small latching clips in the front that simultaneously need to be released. Use two small pins to accomplish this.





I pried the pin out of the connector terminal block by releasing the pin from the terminal block. There are small metallic latches on the side. When pushed down with a small pin, you can pull the wire terminal out of the block. I then used a small pin to gently push the broken pin out of the terminal from the wire side.

To fix this issue, of course, clean out the corrosion and electrolyte residues. I used a swab with rubbing alcohol and some patience. Be careful not to bend the pins in the TPMS ECU connector while cleaning. Also clean the connector housing well. The corrosion is everywhere. This is as good as it wanted to get:





Of course, since now a pin is missing I had to get creative to fix this without having to buy an all-new module. The neighboring pin pairs where not in used on either side of the connector. So, I shifted both KCAN pins over one position towards the inside of the connector. And then I shorted the pins together with a solder ball between the pins:



I put the whole thing back together. I reset all errors:



Normally the KCAN bus error would return pretty much immediately as one may expect. However, that seemed to have stopped after this correction. So, it did get better. I could communicate with the TPMS and everything seemed to work. I drove the car for a few days to see what would happen.

Some of the issues returned. The tailgate is still clicking sometimes, but I had to wait for rain for that to occur. The lights are still dimming, wiper still moves, etc. etc. upon brake application. But the IPC is no longer behaving erratically; the mystery dot does not appear anymore. A scan of the car still shows some KCAN issue and a JBE (junction box electronics) error. No specifics. According to TIS, the JBE controls the tailgate functions, such as the wiper, locks, button presses on the tailgate and the door sensors. There is only one harness into the tailgate. Putting it together I concluded that there must some power integrity issue. I suspected that it may be another corrosion matter.

I decided to follow the harness running from the JBE in the front dashboard (behind the glove box). Lucky for me, starting back near the TPMS location, I found the issue actually rather quickly. It was a loose ground terminal block:

https://vimeo.com/305334222

The module just needed to be torqued down for consistent contact. How it got loose is a mystery. Probably forgotten be a technician.

I hope this helps for some of your 3-series enthusiast out there. Enjoy.

[krhodes1]

Superb diagnostic work!

[nsjames]

just wanted to say that I found EXACTLY the same issue in my 08 e91.
adjacent modules were mint. Even had the same pin broken off in the connector.

I removed it and coded to FTM, rather than repair the TPMS system.

I had persistent kcan errors, but they never caused issue.
I'm going with everyone needs to check their RDC modules for corrosion, because it's not moisture that's causing this. There was no water staining anywhere in my cargo area. Bone dry.

edit: my build date is 10/07, so this is at least a multi year issue.

potato phone pics

[POBEP]

rt7085 - thank you for incredible diagnostic effort!

I got same KCAN errors on my 09 E91, along with identical RDC module pins corrosion and the very same broken pin.

I spent my teenager days building PCB's myself.
I'll start with replacement ebay takeoff unit for $30.
If that will not work, I'll be looking for my soldering iron in the garage.

My guess is that (copper) corrosion comes from the factory flooded battery.
I remember cleaning up residual electrolyte at the bottom of the battery bay.
I hope that new AGM battery produces less acid fumes.

[rt7085]

Interesting theory as I never found a leak or the like. But them why is everything else not corroded around that area? Mine is still working ok; I have not had issues with the TPMS. But maybe it is just a matter of time!

[POBEP]

Originally Posted by rt7085

Interesting theory as I never found a leak or the like. But them why is everything else not corroded around that area? Mine is still working ok; I have not had issues with the TPMS. But maybe it is just a matter of time!

My hypothesis is as follows:

Overall BMW build quality is high.
Hence, there is very low chance that any items in the battery bay are affected by the acid battery fumes (it just not strong enough)

As you noted, RDC module is very well built (inside) too.
Its PCB has decent amount of clear coat the prevents any liquid from reaching IC components.
In fact, there is so much clear coat that even harness connector is coated from the inside.

With one exception - the actual connector and the harness section outside.

It appears (to me) that
- RCD gold pin coating is way too thin.
- the corrosion is mostly at the pin base points (pins tips are not affected)
- E91 RCD module position allows some vapor to condensate in the connector area
- over the years, light acid fumes condensate does its job.

[krhodes1]

Originally Posted by POBEP

My hypothesis is as follows:

Overall BMW build quality is high.
Hence, there is very low chance that any items in the battery bay are affected by the acid battery fumes (it just not strong enough)

As you noted, RDC module is very well built (inside) too.
Its PCB has decent amount of clear coat the prevents any liquid from reaching IC components.
In fact, there is so much clear coat that even harness connector is coated from the inside.

With one exception - the actual connector and the harness section outside.

It appears (to me) that
- RCD gold pin coating is way too thin.
- the corrosion is mostly at the pin base points (pins tips are not affected)
- E91 RCD module position allows some vapor to condensate in the connector area
- over the years, light acid fumes condensate does its job.

One thing though - you do need to make sure that the battery vent hose is in place and nor plugged up. I could see an improperly vented battery causing issues - especially if it is not registered correctly and being overcharged. And those two things would probably go together...

[nsjames]

My battery vent was hooked up when I replaced the BMW battery, and was still hooked up on the replacement battery that was in the car for two years before mine failed.

so I can't imagine fumes did it.
I've been happily living with just the FTM, swapping wheels all willy nillly and what not. Coding even persisted properly through my ccc-cic upgrade.

[POBEP]

Originally Posted by nsjames

My battery vent was hooked up when I replaced the BMW battery, and was still hooked up on the replacement battery that was in the car for two years before mine failed.

Same here - vent was hooked up and new battery got vent plugged-in too.

However, I clearly remember wiping out some electrolyte at the very bottom of the battery bay (when I replaced factory flooded battery).
It was not per-say "visible" puddle, but certainly was not a plain water liquid.

I just can not imagine that gold-plated copper pins can corrode without "help" from external source.

[nsjames]

Originally Posted by POBEP

Same here - vent was hooked up and new battery got vent plugged-in too.

However, I clearly remember wiping out some electrolyte at the very bottom of the battery bay (when I replaced factory flooded battery).
It was not per-say "visible" puddle, but certainly was not a plain water liquid.

I just can not imagine that gold-plated copper pins can corrode without "help" from external source.

maybe someone spilled it when wedging a battery in there.

mine had nothing of the sort, everything in the entire quarter panel was dry as a bone. There was dust in there with no fluid tracks.

which only added to my confusion as to how the RDC sustained corrosion to such a degree.

[bman142]

Found the exact same pin corrosion on my 08 328xi E91.
I do see a little liquid at the bottom of the battery tray so MAYBE that is related?
I suspect it's just from 12 years of use at this point.
Now that I think of it, going to check the pins for other modules in that same area.

[nsjames]

Originally Posted by bman142

Found the exact same pin corrosion on my 08 328xi E91.
I do see a little liquid at the bottom of the battery tray so MAYBE that is related?
I suspect it's just from 12 years of use at this point.
Now that I think of it, going to check the pins for other modules in that same area.

I checked all the other stuff on mine.
they were all fine. Only the RDC module was corroded.