CAN-Bus not communicating with anything
 

On my 2003 base model, I have a lot of electrical gremlins I've been tracking down since I bought the car. I finally bought a Foxwell OBD reader, and I got a plethora of codes. They include "CAN-Timeout, Instrument Cluster-No signal (DME, ABS, PCM, Air Conditioning, Fuel Level, Oil Level, Airbag), and what I believe the problem is actually, Instrument Cluster (No Signal B+, and Implausible Signal Power Supply)". I will list the code numbers at the bottom of this post for anyone who is interested. The Porsche troubleshooting manual recommends replacing the instrument cluster for most of the no signal faults, but for the last 2 that I have a hunch about, it suspects wiring, and I also suspect an open in the CAN-wires. I have no problem checking wires with a multi-meter, but I don't have a good bearing with where these wires might be located in the vehicle, weather this might be a CAN-hi or CAN-lo problem, and what some likely spots my issue might be at (ie grommets through the firewall, etc). Additionally, to my knowledge the 2003 model year is the first model year to have a CAN-Bus, which has made my search for information difficult (shoutout to charm.li for having manuals). I may be on the wrong track entirely, but I would really appreciate any insight into this problem!
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Code list; P1601, P0071, P1576, (Instrument Cluster) 36, 9110, 9111, 9114, 9115, 9122, 9123, 9130, 9131, 9140

Your assumption that this is a wiring problem is likely a good one. I chased similar gremlins in a B5.5 Passat some years back. The culprit turned out to be a broken CANbus wire in the flexible bundle going to one of the rear doors. Took months, on and off. To find it, and about 10 minutes to effect a temp repair to it (solder and shrink tubing).

It’s tedious work, no question about it. Wiring diagrams in the Bentley aren’t totally awful, so use them as best you can.

Thanks tcoradeschi, I appreciate the insight and I will consult the Bentleys. Did you have any rhyme or reason when looking in the door wire bundles? I'm thinking that's a reasonable spot with high wear, and thus a good place to look, but was there any other reasons you checked there?

Oh, boy. Time to put in my thinking cap, as it’s been 10+ years.

The B5.5 (this was an 02 Passat wagon, V6, 5-speed) has two CANbus circuits: a high speed circuit, which was tied to mission critical systems, ie engine controls and the like, and a low speed circuit, which was tied to all the rest. The latter included HVAC, audio, power windows, etc.

We started seeing flaky behavior in the low speed systems - radio would not turn off when exiting the car, heat controls would not work, and all of it was random in nature.

After doing some parts swapping (used HVAC controller) to no avail, I ended up with a knockoff OBD2 cable, the free version of VAG-COM, and doing repeated scans (at this point the car was our eldest child’s DD during her senior year in HS) when I could. It showed error msgs of some sort in the low speed circuit, so learning what was on that circuit was the next step.

At some point, we realized that one of the failures was the ability for the driver to raise and lower the window in driver side back door. The door switch itself would work, but not the switch on the driver’s door.

After that, it was just basic inspection of the wiring, and if wiring to a door fails, the flexible bit in the door jamb is a logical place to start. Sounds simple, but probably took a couple of months, when it was all said and done.

I have no idea what’s on the 986 CANbus, so getting smart on that would likely be your first order of business.

Hope this helps some.

Not an expert on this, but maybe someone with more knowledge will correct me or it is already helping you out a bit.

As far as I am aware there are two CAN busses on these models. One for the powertrain and one for the comfort / hvac stuff.

On the cluster:
Yellow: CAN comf high
Black: CAN comf low
Blue/White: CAN antrieb high
Gray/White: CAN antrieb low

ABS is on CAN antrieb
DME / ECU is on CAN antrieb
Tiptronic is on CAN antrieb

Radio is on CAN comf
Clima is on CAN comf

It looks like the CAN antrieb wire colors are also used for other functions in the engine wiring loom.

Thanks Marc_986, that's very helpful. From what you're saying, I have a problem with both CAN-systems, which in my opinion would rule out the CAN-data wiring having a break somewhere being an issue.

That leaves me with the instrument cluster being faulty (seeming more likely now), or an issue with the CAN-power supply wiring, if such a thing exists.

I don't believe I clarified, I have no noticable issues with my instrument cluster. Whatever the problem is, I believe it is isolated to the CAN-computer.

By any chance, does someone know the pinout of the connectors on the instrument cluster, and which spots the CAN-related pins are? I think my next step should be to check for voltage at the power supply pins. If that check passes, replace the instrument cluster, and if not, repair the wiring.

Other than the codes you see, what are the issues you are tracking down? If none, wouldn't it make sense to try another code reader? As far as I am aware the code reader would still only communicate over the diagnoses bus (assuming this is LIN).

The instrument cluster in your car does not have a speed input. So it will get speed info over CAN from the ABS unit. If that works, the CAN is operational. If cruise control works it means that speed info also comes from ABS to DME.

I have a few other issues, and I think they are related. Upon opening the doors (the initial power on of the vehicle systems), my radio pops and static comes out of the speakers and the radio does not work, the air conditioning control panel sometimes is unresponsive, and the instrument cluster sometimes has all the lights on and the readouts do not work. The radio can be corrected by removing and reinserting the fuse, ie resetting the system. The other problems take about 3 to 5 minutes of the vehicle powered on to correct themselves.

Also, I cannot clear my Airbag fault light, and I have a hunch it is because the reader isn't able to communicate with the airbag computer through the CAN, but there is a chance the reader is not capable, although it is advertised to clear it.

My speedometer and cruise control do work.

All of these real issues seem to be comfort-CAN related to me, maybe that is where I should check first. But it does not explain all the codes I have.

Also, what does LIN mean? I am unfamiliar with the diagnoses bus.

I agree, start checking the comfort CAN wiring. Seems like a bus very local in the dash area, so probably not the worst to check.

CAN does not have it's own power defined, it uses differential signals and can tolerate very high voltage differences between the units on the bus. So just check the high and low individually.

If wiring checks out ok it probably starts to become a matter of removing units from the bus and checking.

Awesome, mega thanks to you Marc_986! I will be checking the comfort-CAN wiring shortly! Thanks for bouncing some ideas off me.

Some other thoughts I've had brewing; since my problems are so isolated to the vehicle initializing, what other components might be included in that system?

I know in older model 986s, the ignition switches are a common problem for mysterious electrical gremlins. However, in newer ones (2002+ maybe? Whenever Porsche switched from the black switch to white) the issues seem to be generally fixed, and I wrote it off when I saw a JFP forum post say he had never seen one of these newer style units fail. I have one of these newer white switches, and I have one on order. I plan on swapping it for funzies. Its my only non-CAN guess.