Mk8 Fiesta fault codes and airbag light

[lphuk]

Just bought a Mk8 (2018MY) 1.1 Fiesta for my son to learn to drive.

All good when purchased (privately) but air con needed re-gassing.

When I got the car home after buying it I hooked it up to Forscan and checked for codes etc. There were some stored codes which I cleared. After using the car a few times I did the same and found codes some related to AC pressure etc. which I expected but lots of others that all had a common theme, and open circuit or earth issue. Things like rear left taillight, handbrake switch, fuel pump, horn relay etc. Mostly listed under the Body Control Module section.

Cleared again and used the car. Then checked and no errors.

Took it for an aircon re-gas today. They did the usual tests, pressurised the system, checked the pressure switch operation and AC clutch etc. and all checked out fine. Re-gassed the car and then tested the AC. The radiator fan won't come on as it should when you switch on the AC. They plugged in a scanner and all the signals and info checked out - just no movement of the fan. So looks like the fan might be knackered. Not a massive issues and fairly easy to replace.

But....when they were doing the AC and checking with the OBD reader and airbag light came on. Never seen that before. They cleared it and it didn't come back. I drove the car home and all was OK. Then whilst I was sat checking codes again on Forscan it threw an airbag light and it won't go out. Checked other codes and again I've got lots of 'ground' type faults. I've run the PCM, BCM , GFM, ABS etc. etc on demand tests using Forscan and they all return no issues. And everything works in the car, there are no issues 9apart from the rad fan and airbag light now). The car never throws a general MIL.

Errors include a few U0401s a U1012, all the grnd issues appear in the BCM.

I'm thinking it's a dodgy earth somewhere? I checked the BCM and fuses under the bonnet and they all look OK. Fuses under the glovebox inside look OK too. No obvious corrosion or anything.

Anybody had anything like this before? Any advice would be gratefully received!

I've just ordered a different Forscan OBD cable as for some reason I can't see RSM module when I connect.

Cheers

[lphuk]

Don a bit more digging on the airbag light

Code B1413:13-8B

Driver frontal restraints sensor circuit open.

Could anyone tell me where I might locate said sensor?

Thanks

[TomsFocus]

1 hour ago, lphuk said:

Code B1413:13-8B

Driver frontal restraints sensor circuit open.

Could anyone tell me where I might locate said sensor?

The wording of this fault code is ambiguous.  It seems to relate the crash sensor(s) that are located just behind the front bumper.

The Mk7 Fiesta only had one in the middle, but the Mk8 may have one either side like the Focus.  They are small square plastic sensors.

I suspect one got knocked while the garage was doing the AC regas.

[lphuk]

Cheers - I need to take the front bumper off foe something else to will have a look when I do that.

I did wonder whether 'frontal restraints' referred to the seatbelts and the pre-tensioners on their that are linked to crash sensors / airbags.

 

[TomsFocus]

2 minutes ago, lphuk said:

Cheers - I need to take the front bumper off foe something else to will have a look when I do that.

I did wonder whether 'frontal restraints' referred to the seatbelts and the pre-tensioners on their that are linked to crash sensors / airbags.

If it's like the Focus, you don't need to remove the bumper to reach them.  The sensors are near the top of the slam panel.  

 

[lphuk]

More digging on fan. Removed rad fan from car. Test it in the bench (using the 2 main connectors on fan motor) and it spins fine.

Put it back in the car, and then checked for voltage across the connector to the fan motor when AC is switch on but nothing. 

For some reason forscan won't let me control the fan, no idea why. I can read the fan signal request etc but not force it to run. Which I though I could.

Might have to call an auto electrician in......

 

[Tizer]

5 minutes ago, lphuk said:

For some reason forscan won't let me control the fan, no idea why. I can read the fan signal request etc but not force it to run. Which I though I could.

Not much help but sometimes some the options in Output Control Mode in FORScan do not work even if there is no fault.

[lphuk]

1 hour ago, TomsFocus said:

If it's like the Focus, you don't need to remove the bumper to reach them.  The sensors are near the top of the slam panel.  

 

Cheers - but They don't seem to be there on a Mk8 Fiesta. Nothing obvious anyway.

[unofix]

5 hours ago, lphuk said:

Put it back in the car, and then checked for voltage across the connector to the fan motor when AC is switch on but nothing. 

For some reason forscan won't let me control the fan, no idea why. I can read the fan signal request etc but not force it to run. Which I though I could.

Have you checked both fuses in the engine bay fusebox for the cooling fan ?

9	60 A	High-speed cooling fan.
10	40 A	Low-speed cooling fan.

[unofix]

This the wiring schematic for the cooling fan control

[unofix]

Engine bay view

[lphuk]

Cheers - tested those. Removed both and they look OK and show continuity with a multi-meter.

Next plan is to unplug the coolant temp sensor as I understand this should put the fan on constantly. Should I see 12v across the plug that goes to the resistor at the bottom on the fan shroud if there is a request to run the fan?

Am I right in thinking there are no relays as such for the rad fan and it's controlled by the ECU (PCM)? If I unplug the coolant sensor and still nothing, and no 12v at plug then it could be the PCM output buggered?

[unofix]

There are two relays in the engine bay fusebox but they are none serviceable. If you remove Fuse 9 and Fuse 10 you can test the operation of the fan by applying a temporary 12V positive supply to one side of the fuse holder.

Applying 12V to fuse holder 10 will make the fan run slow. Applying 12V to fuse holder 9  will make the fan run fast. See the circuit diagram above for details.

[lphuk]

Cool that helps cheers - I will try tomorrow. When looking at the fusebox in the engine bay from the front is it the top or bottom leg of the fuse connections?

How do I physically apply 12v to that fuse as the fuse is inaccessible when the box is fitted? Do I do it from the connector contacts on top.

Ignition on or off?

If I get nothing I presume the non-serviceable relays are dead? This means a replacement fusebox?

If I do see the fan spin it's the PCM not outputting a signal? New PCM?

Thanks

[unofix]

41 minutes ago, lphuk said:

How do I physically apply 12v to that fuse as the fuse is inaccessible when the box is fitted? Do I do it from the connector contacts on top.

I would try and jam a bit of wire in the fuse holder if possible and then put the fusebox back together. Of course it will be a guess which side of the fuse holder is to the fan and which side is to the relay. You could do it from the connector on the fusebox but that's probably even harder to get a contact with.

[lphuk]

Removed the connector on the coolant temp sensor. Got the 'overheat' warning on the dash and the fan came on at full speed (I presume).

Not managed to work out how to send 12v to the fan as car won' power up without both of the large connectors to the fuse box attached.

Checked continuity from the fuse box connector to the fan connections and it's there for both. 

So it looks like the PCM can send fan signal request, and the fast speed relay (fuse 9) is working. Relay on fuse 10 dead? Or possible low speed resistor on fan cowl dead? How would I test that?

A quick way to see if was the relay would be to get a replacement fuse box. They are pretty cheap second hand. I can get one with the exact matching par number - is it a straight swap or does in need coding to the car?

 

 

 

 

[unofix]

30 minutes ago, lphuk said:

How would I test that?

Short out the resistor and the fan will run at full speed if the problem is the resistor.

[lphuk]

Bridged the resistor and nothing.....

 

Now need to check if it's getting a 12v signal to the plug connected to the resistor I guess. If not either relay dead or PCM nor requesting?

HVAC self test comes back OK and no codes against HVAC in Forscan.

[lphuk]

Found the issue!

It was the resistor - I just didn't bridge the plug properly the first time.....

So, can I buy a new resistor? Can't seem to find them listed online.

 

Still have an airbag light though ☹️

 

 

[unofix]

eBay: https://www.ebay.co.uk/itm/116108479181?

[lphuk]

Finally got the fan sorted. Bought as working second hand one for £59. Fitted it yesterday and all good.

Used the opportunity to fix some other bits like broken headlamp brackets and removed the bumper to replace the stop slam panel section (also damaged).

This car was CAT S. God knows how. The only damage was bumper slightly damaged, rad surround cracked and (looks like) a broken washer bottle as it's been replaced I think. The structure is total untouched and straight as a die. What are insurance companies doing??

Still have the airbag light. Anyone help with suggestion for that please?

Code B1413:13-8B 'Driver frontal restraints sensor circuit open'

Checked wires and connections under the seat and all look good. I presume this is a seatbelt code and not an airbag code?

Cheers