Hello,

 

I've got an airbag light preventing me getting an MOT at the moment. Diagnostics point to the airbag controller module which I'm booked in to replace. However, I am wondering if broken wires in the driver's door loom can cause the airbag light. I presume there are sensors in the door for side impacts, but I don't know if they would route though the loom. Mine does have broken wires that have been causing issues with the windows but I've delayed repairing them until after the MOT. This might have been a mistake.

 

Can anyone offer any insight or advice? Thanks.

 

Mike

Hi M, when my door loom went, it didn't give a warning light for the airbag or anything else, things just stopped working, like windows. 

Yes if there is a crash sensor in the door.

For the sake of repairing them, a free job if you can do it yourself, worth a try!

Not sure how many airbags your car has, but early delvage into wiring diagrams suggests that side airbag crash sensors are probably with the airbag itself, as there are no  intermediate wiring connections between airbag control unit and sensor. To my mind that means the sensors can't be in the doors, as that usually would entail a plg/skt connection at the a-pillar.

Thanks for your feedback. I did repair the wires a couple of years ago but they've broken again and I'm not sure if wires other then those that are obviously snapped might also be faulty. I'll replace the loom once the MOT is done, but given that the car's done 200k miles I'm reluctant to spend money before it's got an MOT. I was quoted £900 for the airbag part (£1100 with fitting), but I've managed to find one on ebay for a fraction of that. Fingers crossed it does the job. NZ100 and Wino make me feel confident enough that the loom is outside of the airbag issue. I'll crack on and get the part fitted - fingers crossed!

 

Thanks!!

21 hours ago, Mikexsr said:

Diagnostics point to the airbag controller module which I'm booked in to replace

 

What fault code was reported?

Have you checked fuses?

I'd be quite surprised if the module itself has failed.

Scratch that about fuses, there don't seem to be any associated with the airbag control unit, just an ignition 12V feed.  

Interestingly, there's a device I've never heard of upstream of the controller power feed called an airbag energy accumulator unit, J177. Wonder what that's for? and where it is?

J177. Wino, if you dont know, nobody will. 😊

Thanks but surely not true.  Anything introduced in the last dozen or fifteen years is likely to be something I have no direct experience of.  This J177 seems not to have been fitted to the earliest Roomies from March 2006, but introduced shortly afterwards in December 2006.  Trying to think of other changes that happened around then that may have required it, failing so far.

 

Maybe a change in regulations to cover the situation where the accident has instantly killed the supply voltage? So a power buffer, maybe?

Edited 14 August, 20205 yr by Wino
sp

@Mikexsr.Who did the diagnostics???

 

Have you tried simply resetting the warning light??

28 minutes ago, Wino said:

 

Maybe a change in regulations to cover the situation where the accident has instantly killed the supply voltage? So a power buffer, maybe?

 

Thats what it sounds like.

 

I had an airbag controller go on my MK1 Octavia, I didn't even know of VCDS so was relying on a friend who runs a French Kwik-fit type place for diagnostics (snap on tester) I did all the connections but the fault code could not be erased (no comms with unit?) I new nothing about diagnostics & VCDS then.

 

I simply pulled another one out of a car in a scrapyard, did not know to look at the part number, suffix or coding, I just plugged it in and everything worked, probbaly had to get him to remove the fault code, cant recall, it was too long ago.

 

I did later read that they were a common failure and the £10 I had paid was a bargain because they were sought after.

@Tilt I had a Bosch garage run diagnostics for me. They said they cleared one fault but were unable to clear a second. I don't have the tools to clear them myself. They told me I needed to replace part# 1C0 909 605 F and quoted £900. I just had the one from ebay delivered (£12.99). Fitting won't be cheap but I guess I'm going down that route. I had just been worried that it could be something else causing that part to show a fault, rather than the part itself. It doesn't seem to be a part that fails, typically. 

 

The report they gave me identifies two faults:

1. ChecksumError - ECU Defective

2. Supply Voltage B + Signal Too Low - Intermittent

 

@Wino I looked at the fuse map after you said that and I couldn't find anything there either. I had done a fair bit of googling before posting here though and some people had seen airbag lights caused by fuses for wipers... no idea how that works.

 

 

@Mikexsr

Might be worth your while reading this: https://www.airbagreset.com/articles/how_to_fix_vw_airbag_code_65535.html

Haven't yet myself, so don't know how easy the fix is.

 

Edit: Wait, no, looks a bit scammish as I scroll down.

Edited 14 August, 20205 yr by Wino

Unless the Roomster is any different to the MK1 & MK2 Octavia and the Yeti then fitting is easy, you just need the hands and the skills of a gynaecologist.

 

I think they are all mounted on top of the transmission tunnel level with the drivers shin.

That J177 module disappears again for the 2010 and 2013 editions of wiring info, so it looks like it may have been a short-term fix for a vulnerability in the airbag ECU itself?  There's stuff on the Ross-tech site about low voltage being implicated sometimes in the occurrence of this error.

1 hour ago, Mikexsr said:

The report they gave me identifies two faults:

1. ChecksumError - ECU Defective

2. Supply Voltage B + Signal Too Low - Intermittent

 

This might be a really daft question, but does the 2nd fault indicate a battery issue? Presumably fixing that wouldn't solve my ECU issue?

 

I've tested the battery and it sits at 12.25v when off and dips to 8.5v when starting. Occasionally it turns over a little slowly, but always starts. Maybe I've just got a couple of issues at once though. 

 

I should have definitely mentioned this earlier, but the airbag light initially came on about 8 weeks ago at a time when the car was starting badly. The garage told me that the throttle body needed replacing and it's been ok since then. As I said though, it does sometimes start a bit slower than normal (1 in 10 starts, maybe). 

Not daft at all, and the answer is almost certainly yes. I doubt that fixing it will solve it in terms of this airbag ECU but might protect against future trouble with replacement. Do you have a battery charger you could put on it for a few hours?

May not be the battery per se, so much as normal self-discharge and normal parasitic loads bringing it down due to lack of use.

If the battery is the factory original it is probably on borrowed time.  Does it have a VW group part number on the top surface? That's usually a giveaway indication of originality.

 

Diesel or petrol engine? Diesels will probably tend to dip the battery voltage more than petrols at start-up.

Edited 14 August, 20205 yr by Wino

8 minutes ago, Wino said:

Diesel or petrol engine? Diesels will probably tend to dip the battery voltage more than petrols at start-up.

 

Mine's a diesel. I doubt it's the original given the car is coming up to 12 years old. I installed the new (second hand) ECU this afternoon, and am booked in to get it reprogrammed on Monday now. Although it's interesting what @J.R. said about just being able to clear the fault afterwards. If all works out I'll look at getting the battery changed.

 

Bloody cars.

 

Thanks for all your input!

Definitely due for a battery change as it will start to generate all sorts of fault codes & warning lights with that volt drop, a shame because the engines will start easily at that.