Breezy_Pete

Condensers give the appearance of being super-fragile due to the very fine comb of fins that conduct heat away from the much more robust tubing that actually transports the refrigerant around.

Hey, you started it, by poking an 18-month dormant thread back into life. You supplied no information about brake fluid capacity, but just told the OP he didn't need to change it! Pots and kettles.

Are you doing the work yourself? DOT4 is DOT4. No point in buying it yourself if you're not DIYing though.

Cams, throttle body, exhaust, mapping. May be some other things. "We know what you're thinking"...😆

I bought a cheap spare alternator for our Fabia on ebay once. Despite having already acquired a cheap spare alternator for our Fabia from ebay some time before...and I knew that I had done so! Still to use either.

If the breather system is working properly, there should be no positive pressure in the crankcase to force oil past any seals. Do some reading about crankcase ventilation systems (abbreviated to PCV generally), especially for your engine type, or wait for someone familiar with the arrangement to advise you on here.

Fix the breather system fault that's causing the crankcase pressure to be high. What engine does you car have?

Battery voltage is a little low, but not hideous. Thinking of ways the alternator could fail whilst standing for two weeks, all I can come up with is that the carbon brushes have stuck in their holders, rather than being sprung onto the sliprings, so may not be making sufficient contact to energise the windings. If you're feeling 'experimental' try giving the alternator body (towards back/non-pulley end) a few taps with a rubber or wooden mallet, to try to shock them free?

What is the voltage between the battery posts? Best bet is to borrow a known good battery that will fit (any that physically fit, with the terminals the right way round). If that doesn't show an increase in voltage when the car is started, you can be fairly confident that it's not the battery that's at fault. What year is this car? Have you looked at the alternator fuse? Generally the leftmost stripfuse in the battery-top fuseholder.

Presence of auxiliary belt confirmed?

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.

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.

@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.

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?

I'm not sure really mate, but it does look like the valve is misbehaving in some way, if the car works better when it is disconnected. Wait for the confirmation on a longer drive before considering what to do, I think. It is a valve that's driven by a proportional solenoid, with potentiometer position feedback, so a number of faults can occur and be detected by the diagnostics. The P0NNN generic codes aren't as useful as the VAG-specific numerical codes which you could read with VCDS or a handheld scanner with VAG coverage. e.g. 16785 flow rate too low 16786 flow rate too high 16788 control difference 17811 (as above) 17812 basic setting not performed Quite possible that the EGR valve is sticking due to age/wear. When ours failed in that way it generated one of the control difference codes, can't remember which. I think it means position indicated by potentiometer doesn't match position requested by electronics. Your PCV valve may have a slight leak, but not significant/critical if it doesn't change engine behaviour when you block that port, I think.

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?

What fault code was reported? Have you checked fuses? I'd be quite surprised if the module itself has failed.

BKY is 4 pot 1.4L

Always 2 & 3 that shut off in the 1.4, doubt anything changed in that respect for the 1.5 Can probably see at a glance by lumps of actuators over cam cover

I think ignition switch is another possibility. Way, way less likely though.

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.

Do the radiator fans come on? See what compressor shutoff code - if any - appears when it goes from working to not.

That's it. Make sure the drive includes conditions where the bad behaviour was happening. Be careful not to break the connector latch when you disconnect the EGR. Push the connector firmly onto the valve as you release the latch (you may hear it click open), then pull the connector off/away.

I can only suggest replacing the cable from alternator to battery then. May be a part number printed on it.