Electrical Problems - Anti-skid, brake failure, etc

[hughjass]

Current plan of action would be get battery checked from a place down the road.
Don't know how to check alternator, maybe they can do too.

This is the 1.6D drive version, a Volvo guy said this has two batteries, is that true? Where do I find second and could that one have an affect or is it unrelated. When I unplugged the front battery to disconnect CEM, there is no sign of life which makes me doubt there's a second one.. didn't have the time to dig around in boot.

Buy used CEM + send to Volvo diagnostics guy to clone.

Cry if that doesn't solve it.

[pinballdave]

The DRIVe models do have a second battery. I'm glad you didn't have time to dig around in the boot, as the battery is mounted in front of the left hand front wheel. To access it you either remove the wheel arch liner, and then the engine ecu box, or take the front bumper cover off. It is there as a backup battery to keep the ECU voltages up while the starter motor runs in stop-start mode.

There's a complex set of relays and diodes to switch the second battery in and out when it's needed (which I don't fully understand yet!) but I think it is only connected when the ignition is on. Either way, it doesn't seem to cause problems.

Alternator or battery failure can cause communications errors, with VIDA some codes are logged with additional data, so you can check what the battery voltage was when the fault occurred. In theory this can be helpful to track the cause down, but in practice a battery / alternator test is often enough if your fault code reader can't read the logged data.


It's possible that a replacement CEM may be needed, but if you do get a replacement one to clone your old one into, make sure it's part number matches your original one. This will be the number printed directly onto the plastic casing of the CEM. As a 2012 model, I'd expect your one to read 'VOLVO 31327215' followed by a 6 digit date code.

Some people try to match using the part number for the Fuse numbers sticker (31268178), as this is the one that stands out more. But all the different versions of the P1 CEM use this same sticker part number, so you may get an incompatible one if you go by that one.

If buying a CEM from eBay, double check the photos for the correct part number, and check with the seller that you're getting the one in the photo. There are many breakers on eBay who list them by the sticker number, and don't realise there's different versions.

[hughjass]

Originally Posted by pinballdave

The DRIVe models do have a second battery. I'm glad you didn't have time to dig around in the boot, as the battery is mounted in front of the left hand front wheel. To access it you either remove the wheel arch liner, and then the engine ecu box, or take the front bumper cover off. It is there as a backup battery to keep the ECU voltages up while the starter motor runs in stop-start mode.

There's a complex set of relays and diodes to switch the second battery in and out when it's needed (which I don't fully understand yet!) but I think it is only connected when the ignition is on. Either way, it doesn't seem to cause problems.

Alternator or battery failure can cause communications errors, with VIDA some codes are logged with additional data, so you can check what the battery voltage was when the fault occurred. In theory this can be helpful to track the cause down, but in practice a battery / alternator test is often enough if your fault code reader can't read the logged data.


It's possible that a replacement CEM may be needed, but if you do get a replacement one to clone your old one into, make sure it's part number matches your original one. This will be the number printed directly onto the plastic casing of the CEM. As a 2012 model, I'd expect your one to read 'VOLVO 31327215' followed by a 6 digit date code.

Some people try to match using the part number for the Fuse numbers sticker (31268178), as this is the one that stands out more. But all the different versions of the P1 CEM use this same sticker part number, so you may get an incompatible one if you go by that one.

If buying a CEM from eBay, double check the photos for the correct part number, and check with the seller that you're getting the one in the photo. There are many breakers on eBay who list them by the sticker number, and don't realise there's different versions.

Can't say it would have impossible that I would have hastily bought any old board 😬.

Took the Cem out for a few days, upon reinserting there's only the check engine light. No flickering of the radio today. After starting the car I let it idle and all seems fine. I clear the codes and check again. There's a fault with something unrelated.

The kicker here is that as soon as the brake pedal is pressed, the fault lights will return about brake failure and antiskid. And intermittently the wipers came on, forgets the mileage, etc. All the high speed issues. And sure enough the reader shows communication faults.

Not sure if this means anything but was curious. The battery voltage is still a bit low as it was only taken around the block a few times and just idling. 11.8v off to 13.6v when engine on idling.

I did the "recessive" test with the Obd and got a reading this time. (I was using the wrong pin).

4 14 1.72v
5 15 1.65v
4 6 2.11v
5 6 2v
So no short?

I've been told we've booked it in at a place next week, let's see how that goes...

[hughjass]

Looks as if this garage has no clue about proper electrical stuff, just saying things I know already and suggesting an EGR solenoid change or something

Not sure if it's worth doing the CEM swap myself, or finding another garage or what..

[hughjass]

Taking car back from that garage today, anyone recommend anyone who can deal with this sort of stuff near Edinburgh?