Breezy_Pete

I learnt two things this morning, one related to VCDS and the other about the fused feed I mentioned a few posts ago (engine bay fusebox fuse 11). I had always thought that VCDS only worked when ignition was switched on or engine was running. This morning I was looking at measuring blocks of the BCM and noticed that the displayed values kept refreshing even when ignition was off. That's good to know. The other thing was finding that the fuse 11 feed informs the 'voltage reference' as highlighted here: I was hoping that this would correlate with the 'battery'/charging system warning light, but unfortunately it's not that simple. Removing the fuse (with engine running) doesn't trigger the warning light. VCDS (with ignition off) show this when fuse is missing: The 'speech bubble' from VCDS is interesting. I would think that most of the time the engine is running, the voltage at that fuse would be higher than 13.5V (for non-start/stop cars anyhow). Perhaps the speech bubble says a different specification when engine is running? I didn't think to check that earlier.

The Roomster CBZB exhaust is single pipe from cat onward.

I don't have a downloaded facelift mk2 Fabia owner's manual, it should be towards the back of your hardcopy one, I think?

Apologies, I didn't scroll far enough and picked the CBZA data. Should have been this one; interestingly the same, exactly, for fuel efficiency.

Skoda offer these stats for Roomy with CBZB: I would say yesterday's journey would be nearer to the combination profile of journey, so they suggest 5.7L/100km. That's without A/C use for sure, and we all know that manufacturer's data is usually unachievable by at least some margin.

Oil separator and the PCV valve at cylinder head end are new and the internal inlet manifold valve was cleaned out when I found it after inlet manifold removal. That only leaves the valve that allows air entry from air filter, which is original, but works fine. Intake leaks maybe, but all seals on intake manifold were changed when that came off, and the two between turbo and throttle body are new. Vacuum line for brake servo etc. checked carefully. Not at all, as I've said before it is extremely smooth and near silent at operating temp when heard from driver's seat. Difficult to say, because I've never driven another car with this engine, in any condition. Thanks, me too. Which data?

It did 47mpg on yesterday's journey, 120 miles/3hrs home from alternator replacement location, with A/C working hard all the way.

As it was last time we discussed this, approx 45mpg, which is 6.3L/100km I think. I honestly don't think this is a problem for a Roomster with this engine on factory ECU software.

No, they were cleaned and tested by someone I trust.

I bought a secondhand set of injectors from a low mileage car about a year ago and had them cleaned and tested at a local specialist. Fitted them and noticed no change at all. 😆 Walnut cleaning would probably be more useful, but fitting a younger, less worn-out turbo is the next plan. Also probably new water pump and thermostat housing at same time. Scheduled for August. Between now and then I'm keen to install some voltage monitoring kit in the cabin, looking at both alternator output voltage and battery terminal voltage. No longer trust the car's resident warning system!

No, but that's way beyond being worth trying to save. I did refurb the car's original alt, but it's a right faff on the Valeo designs, and I wasn't very happy with the result. I did fit a new slipring assembly, which was pretty cheap, but I wouldn't bother again. Only paid £109 delivered for this aftermarket new one. The alt that the post-mortem pictures are of was sold on ebay as being from a car with only 50-odd thousand miles on it. In 6:6 (metric of 20:20) hindsight, I call BS!

Just did a quick post mortem on the alternator that I fitted approx 16 months back. As soon as the rear cover came off I could see that this was not a recent voltage regulator/ brushpack. I must have misremembered that. As the brushpack came away, big clumps of brush dust fell out. Both carbon brushes were pretty short, but the outer slipring is the standout feature! No wonder it was struggling.

The 107 passed. 😁

Got back to the car in Ely at around 9.30 last night. Set about swapping in my new alt at about 6.30 this morning. Back on the road homeward by 9, home just about noon. I was persuaded by my sister not to hang around until 3pm to be there for when her 107 comes out of its MOT. Que sera, sera. New, 140A alt (thanks for that idea @stigma ) working well, as was the A/C fortunately! 😎

Dud you check the blade fuses under the cover to the right of the strip fuses on battery?

The fans are wired in parallel, so both should come on. Hissing suggests low refrigerant level, when was it last checked? Can you scan the HVAC module for fault codes?

Only other thing that may be worth considering is that it's not hard to completely remove the door. Unplug electrics at A-pillar, undo checkstrap and two 13mm nuts - one at each hinge - and you can carefully lift the door off. That opens up the possibility of inverting the door to get help from gravity to move the glass. An assistant is very useful to take some of the weight of the door during removal and especially re-mounting it.

If you unscrew and remove the motor, you may be able to pull the glass up manually. Edit, apologies, re-reading your post I see you already tried that.

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?