Breezy_Pete

If you go up and down the menu structure from that page, you can look at every part on the car (that is available as a spare part). I didn't see anything helpful on the diagram of the wheel arch trim either just now.

On cars without start/stop there's no BMS, and the alternator isn't LIN-controlled, it just has a voltage regulator inside that attempts to maintain a constant output voltage of around 14.3V (at operating temp). I think there may be a dedicated BCM input for battery voltage monitoring, from fuse 11 on battery fusebox. Described in BCM pinout as "Input of fuse in fuse holder A on the battery (30 analogue)". Next pin is also called "Input (31 analog)" which hints at 'clean' references.

Diagram plus part number table here: Car Parts Catalog - LLLParts

Something that needs investigation after the car is repaired and brought home... ...Apart from seconds before total shutdown, the charging system warning light (red battery symbol) didn't appear (I'm told, I wasn't in the car). And when driving for a total of about 60 minutes with little or no alternator charging happening, with new battery reading (at ciggy lighter skt) as low as 12.1V at times, still no warning lights at all. My partner was frequently probing the cigarette lighter socket with multimeter probes as I drove back to where the vehicle is parked now. The reading varied up and down by a few hundred mV, mostly about 12.3V, never above 12.5V. Why did that not trigger the warning light for charging system?? The light does come on when ignition is switched on, so it's not a dead LED. VCDS scan done immediately on arrival at breakdown had lots of low voltage faults, obviously, including some modules reporting freeze frame T30 at about 11.5V. Will attach that scan tomorrow. I wonder what the threshold voltage is for 'battery light' to be displayed? Some advance warning seems wise, particularly as power steering assistance completely disappears when voltage drops too low. 🤔

Look at the connector contacts on both sides. I mean the loom connector which plugs into the whole light cluster. You're looking for crusty corrosion, especially on the contacts of the brown earth wire both sides. Look at the male pins on the light cluster connectors too.

Thanks. Alternator change was the first ever job I did on this car, before I'd even bought it, so I know tge method. Don't think O2 sensor needs to come off on Roomster, nor fan shroud. I didn't last time anyhow. Sometimes it's quicker and easier to make more space though, so I'll consider your suggestions. Thanks again.

Only things I can guess is that they are referring to the refrigerant pressure sensor, or the solenoid valve that varies the throughput of the compressor. Ask them which of these is the problem, according to the diagnostics that you have paid for. Whereabouts are you based?

Home safely now, Yaris on the driveway (nice quiet, smooth trip home, just over 3hrs). Old battery on charge, taking a good solid 6.2 amps for the last hour or so, seems to be recoverable. Circumstances suggest that Wednesday will be the next mission eastward, with new alternator and every relevant tool I can imagine on board. Sister's car's MOT that day, so will be good to be there if anything unexpected turns up.

The car doesn't have start/stop.

I can send you airbag wiring info for your car this evening if no-one else does first. I'm on the road for the next few hours.

If you have a place where you usually take your cars for MOT, I would pop in and ask them. I suspect that if all lights (including number plate lights?) are OK, that the warning light cannot constitute a reason for failure. I believe that the 'common wisdom' that 'any warning light is a fail' is simply an urban myth.

Have now ordered an aftermarket new 140A one from Ebay/ Schmitz Rotary in Birmingham, should be with me at home on Mon/Tues. We'll borrow Dad's car to get home and me back here again in a few days. Thanks for the support folks. 🙂

I was wrong about manufacturer, it's a Valeo. The car has dealer-fitted detachable towbar and rear parking sensors, but I suspect the alternator was not changed from factory supplied one at the time. It's on the PR list as 110A. I will try searching 03F903023D - Bosch 140A instead, thanks @stigma

110Amp, 03F903023E is the genuine part number, to suit 2012 1.2 tsi Roomster. Think it's a Bosch. If anyone knows where I could buy something plug and play compatible within about 40 or so miles of Ely, Cambridgeshire, please let me know. 🙂

Pretty sure I fitted a new regulator/brushpack before I fitted this (genuine, 2nd hand) alternator only 16 months ago, so I think it must be one of the diodes in the alt that has failed. I'll try to test how much ac ripple voltage there is when it's running, tomorrow morning.

Thanks. Just checked and this one engages and turns rotor in the clockwise direction, as expected. If rotor is wedged it freewheels with anticlockwise turning of pulley, again as expected. Can't blame that I reckon.

Check fuse 11, and message me if that is OK. I can potentially lend you a known good driver's side motor (which is the master of both). If that fixes everything you could buy it from me.

That's cheered me up Gaz, appreciate the sentiment greatly. Hoping it'll turn out to be the pulley, which I have one of at home, I think. Offers of cars from various family members in the short term to get us where we may need to be. 🙂

The third character of the part number tends to be different on parts that have distinct LHD and RHD versions. Double-check for match of that third character.

Sadly not just battery failure. Either alt, or alt freewheel pulley freewheeling both ways (is that possible?). Can't check the pulley for a few hours, at a family birthday in a different car. Not finding a replacement alt showing as collectable at either GSF or ECP within at least 25 mile radius. ☹️

Looking that way. Just picked up a replacement battery only a few miles away. Fitting it shortly.

Front suspension change was unremarkable really, did take a few pics I think which I may add later. Unfortunately right now I'm en route to Roomster breakdown. Somewhere in Norfolk, following a what3words address. Fortunately I had just finished an oil change on my sister's car, and we are under an hour away. VCDS and a few tools on board, but I'm not wildly optimistic of an easy fix. Reportedly a succession of warning lights came on, followed immediately by major power loss and luckily a safe spot to pull over into. Allegedly not even turning over now. 🥲

What makes you think the wiring has been changed?

You may be able to do the nearside, but offside won't usually go low enough due to driveshaft bumping into stuff.

Trusting what ECP, Autodoc etc. suggest for compatibility is often a bad idea.