I have a Ford Focus (DA3/MK2) and a small budget. Recently some parts of my instrument panel / dashboard stopped working so i plugged in my ODB2 bluetooth thing and read the diagnostics codes. From that i found error code U1900 which is apparently a problem in the Canbus communication. After some searching i have with reasonable certainty found out that the canbus terminator on the ODB/PCM end of the bus is not functioning anymore, i measure a very very high resistance when i disconnect the instrument panel on the canbus cuicuit, this is what led me to this conclusion. It may very well be just a bad contact but to be honest i have no idea even how a ECU/PCM device looks and i am also unable to locate it.

Is there anybody so kind to give me some advice? I have written some questions down but the main thing that i want ofcourse is just fix the problem or at least hand it over to the garage with exact information so that they can skip the troubleshooting.

1. Is this something a person relatively handy and knowing about electronics but without a lot of car mechanics experience can further diagnose / solve?

2. Can i reach the ECU/PCM without taking the whole car apart? (for instance just to pull the plug and put it back in to improve the contact)

3. Can i replace just the terminator or would it involve replacing the whole ECU/PCM?

Many thanks!

Anton

Edited February 19Feb 19 by AntonBoutkam

It's probably just the common MK2 Focus Instrument cluster fault

Cracked solders on the board

Contact @rd457 on here, he'll sort you

2 hours ago, AntonBoutkam said:

From that i found error code U1900 which is apparently a problem in the Canbus communication.

Such codes are a common symptom of the common problem of cracked solder joints in the instrument cluster, which the MK2 Focus, both facelift and pre-facelift are plagued with. However there are of course also other possible causes, and it is my understanding that sometimes the odd Uxxxx code can simply be caused by use of a scantool, so you can end up chasing a red herring.

In this case, since you've removed the IC and found what appears to be a major issue with CANbus resistance, maybe something else is going on, instead of or in addition to the common IC issue.

First of all note that not all scantools are created equal. Price does not matter. Some tools can only recognise generic codes, and may ignore manufacturer specific ones, and some tools will only retrieve codes from the ECU, ignoring those held in other modules, so it could be that you're missing a bunch.

Next, double check that high resistance reading. Short the probes of your meter to check that there's nothing wrong with your meter itself. Check that the probes are clean. Sometimes poor probe contact can give false readings. Also, double check that you're probing the correct pair of wires.

If there really is a very high resistance reading on the CANbus with the IC removed, that would indeed indicate a problem. I'm very surprised that there's only one Uxxxx code resulting from it though.

Which CANbus are we talking about btw? The MK2 focus units have two. Both have a terminating resistor in the IC, while one has its second terminating resistor in the ECU, and the other in the GEM.

Also, how high a resistance are we talking? With the IC removed, the resistance should be 120 Ohms. If the module with the other terminating resistor was also unplugged, or otherwise the connection to the terminating resistor it holds was severed, the resistance reading should be 'OL' (over limit / open loop). Perhaps your meter oddly displays its highest possible reading rather than 'OL'?

If this high resistance is real, the problem could conceptually lie with the other module with a terminating resistor (ECU or GEM), but it could also lie with wiring/connectors. To figure out which you'd need to unplug the other module, and then test the CANbus pins of the module, and the wiring, separately from each other.

In the facelift MK2 Focus, the ECU is fixed to the side of the battery box. I can't remember if it's the same for the pre-facelift. The GEM is located in the passenger footwell. The ECU and its connector are not easy components to remove. The connector is held in place, plugged into the ECU, with a bolt which can only be removed with use of a drill! If you want to know what the ECU looks like, you could google "ford focus mk2 ECU".

2 hours ago, AntonBoutkam said:

Is this something a person relatively handy and knowing about electronics but without a lot of car mechanics experience can further diagnose / solve?

It depends. Presuming it's the CANbus that includes the ECU that's faulty, then if you could find the ECU and successfully complete the task of drilling away the special bolt which secures the ECU connector in place, then you could disconnect the ECU and check the resistance of the ECU CANbus pins and the wiring separately to narrow down the location of the issue. If it's the CANbus with the GEM, then that's a whole lot more simple. It can be a little fiddly getting the GEM in and out of place, but no tools are required to unplug connectors. You do need to be able to figure out which pins of connectors/modules are for the CANbus(es) though, which requires you or someone else consulting wiring diagrams.

3 hours ago, AntonBoutkam said:

Can i reach the ECU/PCM without taking the whole car apart? (for instance just to pull the plug and put it back in to improve the contact)

Yes, if it's located on the side of the battery tray as discussed above, though as discussed above, there's a big complication to being able to unplug the connector.

3 hours ago, AntonBoutkam said:

Can i replace just the terminator or would it involve replacing the whole ECU/PCM?

Not sure what you mean by 'terminator'. Firstly let's double check a bunch of things as above, and see whether or not the ECU is even relevant. If it is relevant, the problem is far more likely to be the wiring than there being anything wrong with the ECU itself. The ECU is sealed in a metal case. The pair of CANbus pins are connected together internally through a 120 Ohm resistor (or pair of 60 Ohms resistors in series), and then in parallel connect to CANbus microchips. The only way for a resistance higher than 120 Ohms to be present in the ECU itself is if that simple connection between connector pins and the 120 Ohm resistor was damaged. While this is a common problem for the instrument cluster (for which I personally offer a UK repair service), I'm not aware of it being a problem with the ECU. Almost certainly it should be a problem with the wiring or an intermediate connector somewhere.

Wow, thank you for this help, did not expect such an elaborate message, thank you!

1. I took the instrument cluster apart and soldered those joints as i found on Youtube that this is the most common problem. Then i put them back in place but nothing changed.

2. The cirquit is called comfort i believe, my direction lights are not working (for instance) and the central door locking mechanism is not working anymore. When i press the button on my key i do hear a relay clicking in the car but the doors remain locked.

3. My driver side door lock was a bit crappy when used manually so this is a part that is a bit suspicious but from what i found online this is probably not the problem.

4. When i measured on, i believe pin 6 and pin 14 (from my head) but the canbus pins on the ODB connector i measured 120 ohms initially but when i removed the instrument cluster i measured something in the order of Mega ohms, could very well be open ended i guess with interference (not 100% sure this is possible).

5. I did double check the resistance reading, took the measurement twice and then again when the instrument cluster was attached and they remained 120 ohms when connected close to nothing when disconnected. Ofcourse close to nothing may also be a bad sign but it should be 120 without the instrument cluster and 60 with right?

6. There is another error indicating something about a valve, i think air intake but because Canbus is only working partially on that cirquit i am not sure if this is related and if i can actually trust any other readings.

7. I tried to find the ECU, removed the battery but all i found was a fuse box (next to the battery) and nothing begind the battery but there was a metal plate. Should it really be there? then i will just try again.

8. Thanks i will google it.

Thanks again and i do not exepect you to answer all my questions, you have already been very kind. I will try to locate the ECU again and otherwise just go to the garage i guess.

Have a nice evening /day

The PCM is in different places depending on which engine you have.

Most are in the front left wheel arch, just behind the arch liner. Sone are next to the battery. All have security bolts so you cannot simply unplug them.

23 minutes ago, AntonBoutkam said:

but it should be 120 without the instrument cluster and 60 with right?

Correct.

23 minutes ago, AntonBoutkam said:

i believe pin 6 and pin 14

Yeah that's the standard CANbus pair. The other pair is on pins 3 & 11 if I remember correctly. The one on 6 & 11 should be the high-speed CANbus which includes the ECU/PCM. The other is the Mid-speed CANbus with the GEM.

26 minutes ago, AntonBoutkam said:

direction lights are not working (for instance) and the central door locking mechanism is not working anymore

The GEM has a lot to do with lights and locks, so you likely have a faulty GEM or some corrosion on one or more connector pins.

1 hour ago, AntonBoutkam said:

measured 120 ohms initially but when i removed the instrument cluster i measured something in the order of Mega ohms, could very well be open ended i guess with interference (not 100% sure this is possible).

1 hour ago, AntonBoutkam said:

I did double check the resistance reading, took the measurement twice and then again when the instrument cluster was attached and they remained 120 ohms when connected close to nothing when disconnected. Ofcourse close to nothing may also be a bad sign

Definitely suspicious.

The GEM module itself it located within the housing of the passenger footwell fusebox, which also houses a bunch of fuses. If I remember correctly a whole bunch of wires pass through this fusebox, with it effectively acting as a combined fusebox/junctionbox/module, so maybe the high-speed CANbus that involves the ECU/PCM goes through here, and considering the lighting and locking issues, I'm very suspicious that your passenger footwell fusebox has some corrosion on the connector pins.

Thank you very much! (-: Both answers are probably helpfull, i have something todo tomorrow after work. (-: