JohnBS

Thanks for your help in clarifying which docs apply to which car by date of manufacture!

Yes, I think you're right! J538 on RHS

Having trawled through the schematics I have (relating to the CDAA engine code) - it looks like there may be no relay: rather, a fuel pump control unit

Yes, ditto: there are so many versions of the schematics, it gets ovewhelming. My reg is FT11 JZP John

Here's the other bank: both layouts are for RHD Octavia II

This is what I have for the Octavia relays under the dash: D2.2 is listed as fuel pump. But on my car only two of thse relay are present: D5.1 and D2.1, neither labeled as fuel pump! ( 2.1 Horn relay)

See post of 22nD May

I'm not entirely convinced that it's a battery problem: at lower temps the battery voltage is actually higher. If the issue is actually related to, say, the fuel pump then it might make sense in that this electro-mechanical device is "stiffer" when cold? The appearance of unrelated warning icons confuses the issue.

Yes, erWin Skoda. Massive file with all the engine, saloon/estate RH & LH drive options so it takes some time to find the appropriate data, and then it's a mico-circuit, not the bigger picuture.

OK, so here's the results of today's experiments. Starting with the currnetly installed battery, (which is one which was removed a couple of years ago and has been used as an emergency spare.) It has sat unused in the car for a few days. V as found, no load 12.55V V with ignition & radio on: 12.2 dropping to 12.15V (measued on battery terminals) Current taken by ignition + radio: appprox 7.5A Remove battery and replace with the one removed at the end of April (a newer example of the same blue Varta ). This battery was charged about a week ago, then left standing. V as found 12.8V Current taken by car in fully passive off-state, alarm disconnected, 25mA mean, wth circa 1 second pulses. Ignition on for a few seconds, then off again V battery now 12.64V With ignition on (and fan running) 12.2V There is significant current drain (c 2A) lasting for about a minute after switching ignition off . So, the terminal voltage of both batteries falls from around 12.6V to 12.2V with a load in the 7 to 8A range. I have found a paper which models this behavior, but it was for a 96 AH AGM battery. Accurate circuit model for predicting the performance of lead-aci.pdf

Roy: it's been OK so far, and i suspect the relay swap may have been responsible. The trouble is, merely going in and disturbing things could have caused the issue to go away. My hunch would be try swapping the two relays marked 646 (under the steering wheel). There's still something odd about battery voltages: I'm about to conduct a further experiment with a variable power supply. John

Update. I ended up downloading the schematics from the Skoda database: 2700 pages of pdf. - I've wiggled all the fuses, both boxes, and cross-swapped all the relays with identical type no's. - the battery voltage was slighly low at 12.2(5) volts, so it was given an overnight charge with a CTEK 5A charger. The battery did not make it to the last holding charge state. - after a short time & ignition load the battery voltage dropped back to 12.3 V which is not right for a healthy charged 12V battery, However, the car has not had a problem starting since these interventions, and the stability control icon goes out @ ignition position. I've now fitted a voltmeter module in the cabin, and also swapped out the battery for the one it replaced a couple of years ago. I'll report back if the problem recurs.

From the handbook: "The working life of the alarm siren is 6 years. " :>( John

2011

Another cause of battery flattening (following a few days of non-use) is the alarm (built-in) battery failing. It tries to charge from the vehicle battery, and in doing so can flatten a good battery over a few days. I ended up removing the fuse feeding the alarm.