I recently took my focus to a car electrical specialist to get the rear parking sensors and the reverse light working again. He could not fix the problem and wrote this in his invoice to describe the problem as best as he could   - 

 "I tried connecting 3 different diagnostic tools but none of them could communicate with the vehicles as they were saying the PCM was blank. Also, while checking the vehicle I noticed that the reverse light didn't work so checked for power at the bulb but there was 0v. i would imagine there is some sort of fault with the BCM because the power comes direct from the BCM, but cannot be sure as we can't connect to the vehicle."

I'm hoping someone on here has a better insight into what could be the issue? I'm likely going to have to take this into a Ford main dealership to get this sorted but want as much information as possible before hand.

Thanks

The communication issue is very likely to be the well-known solder joint problem in the instrument cluster caused by the use of lead-free solder. The reverse light and sensor issue sounds like the gearbox switch, although I'd imagine your specialist will have zeroed in on that first. However since the reverse light and sensors are (I think) controlled by the BCM it's likely the communication issue is the culprit there as well.

This would sound to me like the vehicle is not detecting that reverse gear has been selected.

The signal from the gearbox switch is sent to the BCM. From there the BCM then supplies power to the reverse lights and also a separate signal to the PCM which operates the parking sensors.

I doubt that you have two faults, therefore I concentrate your fault finding to checking that the gearbox reverse switch is getting a 12V supply and that when reverse is selected, that the switch operates and sends a 12V positive signal to the BCM.

 

5 hours ago, Maxfield25 said:

 "I tried connecting 3 different diagnostic tools but none of them could communicate with the vehicles as they were saying the PCM was blank.

The use of 'Generic' code readers (even the very expensive ones) often results in DTC's not been read and modules not communicated with.

Use FORScan which is designed specifically for use on Ford cars.

With all due respect @unofix any 'generic' code reader should at least be able to connect and communicate with the car, just not read the Ford-specific codes.

As I said earlier I imagine the OP's electrician would have checked the reverse light switch early on in the investigation. Looking at the year I still think this is the cluster issue.

That said, I agree Forscan is the diagnostic to use.

Unplug the switch and bridge it out to confirm.  On Mk2 Focus' the switch is a very common failure.  (Unless I was just unlucky...)

Which engine & gearbox do you have?

4 hours ago, mjt said:

I imagine the OP's electrician would have checked the reverse light switch early on in the investigation.

You would certainly like to think so, but having witnessed the abysmal state of fault finding at main dealers I've learnt never to assume and to check for myself. The switch may have been tested and may be working fine but is there actually a supply to it ? Has the wire from the reverse light switch to the BCM been checked ?

Depending on which variant of a 2010 Focus (possibility of 3) then it could be worth checking Fuse 76 (10 Amp) in the passenger compartment fuse box, for the reverse lights. Also Fuse 30 (5 Amp) in the rear mounted fuse box for the parking aid.