I feel like I need to ask wiser people for help. My 2011 Focus previously started showing an engine service light, and there were fault codes across the board, but even after clearing them, the following in particular returned immediately:

• U0001-00-AE High Speed CAN Communication Bus

• P0564-82-2F Cruise Control Multifunction Input A Circuit, Alive/Sequence Counter Wrong/Not Updated

Somewhat more randomly, but occasionally, this has also appeared:

• U0140-00-27 Missing Communication With BCM (Body Control Module)

Then, on a really bad day, these have also shown up:

• U0126-00-2B Lost Communication With Steering Angle Sensor Module

• U0126-00-2B ABS (Anti-Lock Braking System)

Possibly from the very beginning, there may have been these EGR faults, and clearly, they are not the only source of the engine warning light, but at least recently, the following have occurred:

• P042F-00-28 EGR (Exhaust Gas Recirculation) A Control Stuck Closed

• P042E-00-AF EGR (Exhaust Gas Recirculation) A Control Stuck Open

• And I have also seen at least once P1303-78-68 EGR (Exhaust Gas Recirculation) Calibration Failure, Incorrect Alignment/Adjustment

What all of these have in common revolves around the PCM. Sometimes, while driving, there has been a message that hill assistant and related systems are unavailable, as well as a false tyre pressure warning (which, in this car, is based purely on wheel speed data from the ABS). Sometimes, the cruise control does not respond at all, either, but that may also be connected to that update/alive counter fault.

Restarting the car may help, and it at least clears limp mode. Most recently, shortly after I started driving home, P042E-00AF (EGR Control Stuck Open) appeared, and when read from the PCM the position feedback, the voltage stayed firmly around 1V. After restarting, the position signal began moving between about 1.0–1.8V, and the fault was no longer active afterwards.

A local workshop cleaned all the fuse box terminals in the engine bay, and nothing unusual is visible in the PCM/BCM connectors. I myself have mainly monitored the HS-CAN bus with an analyser, and the signal waveforms look good, termination appears to be present at both ends of the bus, and I have not detected any communication errors with the analyser. Also, communication from the OBD port to the different modules has worked without problems.

Other faults, which may be completely unrelated to the above and which I do not consider critical but want to list just in case:

• An old fault present for years: sometimes when starting, the power steering does not activate. Restarting usually helps.

• Apparently, the driver’s seat constantly reports that the seatbelt is fastened.

• B1D26-13-2A Combustion Air Blower (but it has only worked occasionally for years between resets)

The instrument cluster has apparently worked perfectly, without flickering or other disturbances. There have been no starting problems. Apparently, instrument cluster faults are mainly the MK2 model issue?

My own guess so far has been a failing PCM or an issue with its power supply or ground. Experimentally, I have swapped relays R15 and R16, as well as the 50A fuses in the engine bay, MEGA 8 and MEGA 9 (C1617J and C1617K). These did not seem to make any difference. Regarding grounds, I checked the cable coming from the battery and the grounding point next to the PCM coming from the wiring harness, though that does not appear to go directly to the PCM. I haven't identified where the PCM ground is.

The battery was already in a poor condition and the fault code U3003-16-28 was found in memory, but replacing the battery has had no effect either.

It is possible that there are multiple overlapping faults here, but on the other hand, a vast majority could be explained by some electrical issue. I don’t know, but I also find it hard to believe that, for example, a faulty EGR alone would cause such a wide range of faults. But perhaps someone here might have tips on the next direction to take, or what else to check?

Seems the BCM isn't always connecting to the outside world to me.

Edited April 19Apr 19 by anon
thought again

Check the BCM connectors for windscreen wiper fluid ingress (from an internally leaking windscreen wiper fluid pump).

This is a well-known problem on the Focus MK3 that can cause several BCM related problems.

Hmm, that is interesting. I was quite confident that the culprit would be on the engine bay side, since almost every error code comes from the PCM. However, as I wrote, the BCM connectors also look just fine, and there are no leaks or anything visible. I haven't opened the BCM, though.

No, almost every code comes from the BCM. The seatbelt switch has nothing to do with power control nor the ABS, nor the steering angle sensor.

I don't know what to say. For example, these are listed under PCM, not BCM:

• P042F-0028 EGR (Exhaust Gas Recirculation) A Control Stuck Closed

• P042E-00AF EGR (Exhaust Gas Recirculation) A Control Stuck Open

• U0001-00AE High Speed CAN Communication Bus

• U0140-0027 Missing Communication With BCM(Body Control Module)

• P0564-822F Cruise Control Multifunction Input A Circuit

• U0418-0068 Data Invalid From Braking System Control Module A

Not that I'm saying the BCM couldn't be faulty, but fault codes don't usually accumulate under the BCM.

Regarding the seatbelt switch and e.g. AHCM(Auxiliary Heater Control Module), these are for sure whole other issues and at this stage, less interesting. I just decided to list these as well.

I think you are a long way out of your depth. The CANBUS isn't talking to the BCM. The BCM isn't communicating. It needs to be. You now need qualified help as your knowledge has taken you as far as it can.

Yes, suspect water ingress in BCM, early MK3s especially suffered with this

The EGR issues are probably that you do indeed have a faulty EGR

Yeah, agreed, the EGR might be faulty indeed, and that needs to be changed. So far, that has also been the only thing that the two shops, including the Ford service, have suggested. The other faults they cannot pinpoint, but say it "might be a grounding problem somewhere". So other than EGR, they haven't been much of a help so far.

I guess I'll take the hint here and re-check the BCM thoroughly.

15 minutes ago, PPi said:

I guess I'll take the hint here and re-check the BCM thoroughly

Absolutely

If the BCM turns out to be fine you have damaged corroded wires somewhere

Alright, I have an update. Took out the glovebox and BCM. No stains or anything like that are visible anywhere. I opened up the BCM, and it's clean inside as well. Checked the wiring harness connectors next to the BCM, and they all look good.

Interesting observation: After the last 200 km or so, there hasn't been a single EGR error recorded on the PCM. Also, the service light indicator hasn't been lit during this time, even once. However, the U0001-00AE High Speed CAN Communication Bus error returns immediately after clearing PCM errors, but everything works just fine and the car runs great. So I guess I'll just ignore that for now.

One peculiar detail: I was told that the aux heater suddenly started running today. It shouldn't be doing that, since, well, it's been malfunctioning for years already, and on top of that, it was +15°C outside.

So, yeah, good tips, thank you, but unfortunately at the moment, I can't even be sure if the EGR is good or not, or if that also is only a symptom of some electrical issue somewhere - whatever it is, a wire or a failing component.

Check all the earth points, as many as you can, behind the dash, in the engine bay, under the carpet