Hi all. My 2010 octavia 2.0tdi elegance has a fault code p0562.

Low voltage detected. Check engine light is on.

The alternator puts out 14.4 ish at tickover rising to 14.8 or 9 at 1500/2000 rpm.

With a load lights heated seats windows etc it drops to 13.9.

Ive checked the continuity of the two small wires back to the ecu and all seems good. I have a small obd scanner and if i erase the code, and start the car the check engine light goes off. If i stop and restart the engine, it comes back on again.

I have fitted a new battery, so can  cross that off the list. I can see no obviouse signs of corrosion in the connector or wiring, and all the pins on the ecu are there and in good condition.

So. Where do i go next with this ? Im erring toward changing the alternator, but it seems to be capable of a decent charge rate. Maybe the ecu its self has failed? I just dont know. If theres anyone that can give me advice on what direction to go in , i would really appreciate the help. As i am rapidly loosing the plot.lol.

BKD engine code?

Have a look (for corrosion) at the terminals of fuse 13 in the engine bay fusebox. It gives the main power feed(s) to the engine ECU. If that looks OK and is gripped snugly by its fuseholder, consider trying another relay in position 1 of the e-box; that feeds fuse 13 amongst others.

 

Might also be worth cleaning up the ends of the main earth cable between engine and chassis.

Edited 18 May, 20215 yr by Wino

Hi Wino. Thanks for your reply.

The engine code CFH on the timing cover and CFHC, on the lable in the boot.

Ive checked fuse 13 and it shows no sign of corrosion.

Already cleaned the earths.

I presume the e box is where the relays are located behind the drivers lower panel so will take a look at that next.

Ill update when ive had a look at the relays. Thanks again.

I'll check the wiring diagrams again now that I know the right engine code. 

 

E-box is the fuse/relay box under the bonnet, not the one in the cabin.

That same fuse 13 still applies, as does the relay in position 1 of the under-bonnet fuse/relay box.  Fuse 10 in there, a 5 amp one, may also be worth checking.

There seems to be only 1 relay in the fuse box

In the engine bay? That's the one then!

Just looked at the relay. Its clean and no signs of corrosion. I tested it and it clicks, but only showed 0.2 volts through the large connections. I dont suppose thats normal is it? Surely it should be 12. Something?

It will only be switched on when the engine is running, I think?

Measure the voltage (relative to battery negative), when engine is running,  at either side of fuse 10 and/or fuse 13, if they are the fuse types with metal pads at the top to allow such probing.

Edited 18 May, 20215 yr by Wino

Thanks for taking the time to help Wino. Its so frustrating when you cant work things out.

Checked the volts each side of both fuses  14.24 or there abouts. Same as across the battery.

Hmm. There's also an ignition switched feed from fuse 2 in the cabin fuseholder, so measure volts on that one too if it has the metal pads.

 

Just done the same test on fuse 2 with the same results.

 

Last thing I can think of is to examine/clean any/all earth connections that go to the engine ECU. Not sure of exact locations of far ends but thick brown wire(s) coming out of ECU.

Ok. Ill do that. If it is still the same is it likley to be the ecu? . Also how can i test the signal that comes from the ecu to the alternator i believe the blue L wire should be battery voltage, but not sure about the the reading would be for the dfm wire.

Just to be clear. The engine ECU, is the cast aluminium unit with the two multi pin block terminals and an anti tamper device, thats fitted under the plastc panel by the wipers?.  Sorry to be a moron, but i think ive seen it described as the ECM. Or is that something else? Lol

It's almost never the ECU (unless there's obvious water ingress into connectors, or wiring damage, but then that's not really the ECU itself). Your description of it sounds right. ECM stands for engine control module I guess. PCM is another name, Powertrain control module. All the same.

 

The L connection goes to another control unit too, and I'm not too sure which one it originates from, but from experience of my cars I'd expect to see ignition-on voltage minus about 0.6V when ignition is on but engine not running. Once engine is running and alternator working, I'd expect it to exactly mimic alternator output volts. From alternator it goes to pin 70 of the engine ECU, and pin 32 of the brown 52-way at the onboard supply control unit (BCM) in the cabin. If that wire wasn't making it to the engine ECU, it may explain what you're seeing (assuming that it originates from the BCM).

 

DFM is a pulse width modulated signal from the alternator that may go up and down from 12 (nominal) to zero or 5V to zero in a square wave with pulse width (inversely) proportional to the alternator's electrical loading.  You may be able to see this change as loads are added/removed with a digital meter, as you may see an average voltage, depending on how the meter deals with such a pulse train.

Doubt it's relevant unless it sits at one extreme or other full time, but I think that would generate a different fault code. 

 

 

Mmmmm. Much scratching of head's lol. Ok im checking earths at the moment, when i put things back together, ill test voltage at the alternator plug and see what it is. Ive had a good look at the ecu/pcm and appart from some surface corrosion on the cast aluminium top cover, everything else looks clean and  good.

Do you know what colour and position on the ecu the power cable goes to? I can check there if the ecu is getting power. Before delving into the dashboard.

Thanks again for your patience Wino.

The fuse 13 feeds go to pins 3, 5 and 6 with red/green wires. The fuse 10 feed, red/black, goes to pin 92. The cabin fuse 2 feed, black/grey, goes to pin 87.

Earths, brown, are on pins 1, 2 and 4.

 

Oh, and L, blue wire, goes to pin 70, DFM, blue/white, to 65.

 

Good luck. 

Edited 18 May, 20215 yr by Wino

One other thought...

Everything I've written so far has been based on the premise that it's the engine ECU that's complaining about the low voltage.  How has that P0562 fault code been read? Does it definitely originate from the engine ECU?

It said it was low voltage detected. Below 10 v for 1 minute.

What device has been used to read that fault code?

 

Its an ansel vd 500. Small hand held thing.

Ah, OK, so probably only talking to/reading from Engine ECU and maybe ABS system?

 

Ive just discovered that it also reads vag codes. I checked the engine option it gave me and it said 

002751 and 001fe9. Both  had a message below . Dtc not found. Refer to vehice service manual.

Ive only used it on obd so didnt realise that it also gave vag codes. Ive no idea what they mean.

It gives me a list of systems to check. So if you think it may be related to something else i could check.

Not sure that either of those relate to the original one.