v70 tdi charging problem

[mikebo]

Hello everyone, I bought my Volvo (my first) in 2021 with 279k kms and everything went well until recently. I'd driven 21k kms since buying without the slightest hitch and then in May 2023 I had my first problem - the alternator light wouldn't go out. So I changed the regulator (the brushes were completely worn out) with a Bosch Aftermarket item from WoodAuto. The slip rings were worn but not excessively. Since then I've done 6k kms with no problems - no battery light and no charging problem.

Unfortunately the battery light started staying lit/unlit under really strange conditions (strange for me at least, I've never seen this before) and seeing how the Volvo is way more complicated than I'm used to I'm asking if anyone can shed some light.

So about a month ago the battery light started flickering in relation to roads bumps and the acceleration/deceleration of the car. A week ago when I finally got the chance to look at it I saw that the glow plug lead connection on the cylinder nearest the injection pump had broken and that the wire was arcing with the cylinder head.

After fixing the connection I did some tests over a couple of days and came up with these results which I don't understand :

when starting from cold or if the engine's been off for 4/5 hours, the battery light stays off and the alternator is charging at 14.2V. Leaving the engine running while stationary (idling and revving) until it gets to temperature - the light stays out.

restarting the engine immediately or soon after having stopped it - the battery light stays on for 4/5 seconds, goes out momentarely twice in quick succesion then stays on. The battery isn't charging.

The accessory belt and tensioner are in good condition, the alternator pulley (solid tyoe) is turning with the belt. I've reseated the alternator wires plug and checked the tightness of the nut holding the main red cable. I swapped the relay 2/35.

The problem remains and I've done this test at least 3 times with the same result.

Can anyone help?

Many thanks

Mike

[Baffler]

If the original regulator brushes were that worn then other components will have excess wear too. You mentioned the slip rings have wear so you're going to see false readings if there is poor or uneven contact.

Personally, I would have your existing alternator completely refurbished, Google services in your area, and go from there. They will also test it, prior to refurbishment, to make sure everything else is good.

Ohh...and your existing alternator is very well made so don't swap it out for an inferior product. It lasted 300k so try get another 300k out of it

[hal9000f]

Originally Posted by Baffler

Ohh...and your existing alternator is very well made so don't swap it out for an inferior product. It lasted 300k so try get another 300k out of it

Agree with that 100% and recommend refurbishing it completely. I have done that twice for my 1996. 855 TDI, and it's now at 590.000 km still running strong.

What I also recommend is - if you are going to do it in a shop let them refurbish the main engine ground also. It makes a lot off difference, cause it must be pretty oxidized after so many years. So, renewing it gives a lot healthier electric flow. Small thing, but very important...

[mikebo]

Hi Liam, thanks for your reply.

I've rebuilt/repaired a few alternators from simple stuff like changing the diodes upto changing the slip rings and bearings. As you say, it's a good quality Bosch unit and although the rings have wear they're acceptable.

The car's done 6k kms since the regulator was changed and even now the alternator will charge if the engine is started from cold. What I don't understand is why the alternator systematically won't charge upon restart, as tested at least 3 times by myself.

I see that there's a red/black control wire going from the alternator to the item 4/46A:33 (engine control module). Does anyone know what signals/parameters are monitored by the ECU for this connection. For example temperature?

My assumption is that charging is governed by this red/black wire?

Any help greatly appreciated

Many thanks

Mike

[Baffler]

Originally Posted by mikebo

I see that there's a red/black control wire going from the alternator to the item 4/46A:33 (engine control module). Does anyone know what signals/parameters are monitored by the ECU for this connection. For example temperature?

My assumption is that charging is governed by this red/black wire?

Hi, Mike, I'll need to double check the sequence but my understanding is, when the engine is started from cold, the glow plugs and the coolant heater plugs are continually working away in background...I think in 15 minute cycles. This may help explain no charge when up to temp. I'll get back to you on this.

[mikebo]

Hi Liam, thanks for that.
Just to clarify, upon cold start the alternator would charge and the light would go out until the engine was stopped : that is, engine running for 30 seconds (so still cold) or running for 5 minutes (so up to temperature).
No matter what the engine temperature was on stopping and then restarting, the alternator wouldn't charge and the light would come on, flicker then stay on for as long as the engine was running. Same on 2nd, 3rd or 4th restarts.
Going to "play" some more with it, see what happens under different circumstances.
Before this problem surfaced the battery light behaved normally, it went out and stayed out as soon as the engine had been started.
I'm wondering if that arcing hasn't sent or provoked transient spikes into the electrical wiring and so affected the ECU. I don't know for how long it's been arcing, the car's been starting normally
Many thanks
Mike

[mikebo]

Hi Liam, I hope this rabbit hole doesn't go too deep LOL.
Been experimenting and have come up with some interesting stuff.
I started the cold engine and as usual the light went out. I put the A/C control on auto (which I've never used) to demist the windscreen and the battery light came on. Coincidence? Stopped the engine, left the A/C on auto, restarted the engine, the battery light went out and the fan started blowing. Turned the A/C to OFF and the battery light came back on. More coincidences? Repeated engine starting with various A/C manipulations several times and although not repeatable 100%, it did seem to me that the A/C auto switch was affecting the battery light. So searched for 9459769 (P/N for the heater control unit) and found this thread

https://www.matthewsvolvosite.com/fo...c.php?p=452108

the post from jimmy57 at 11.43 is very interesting.
Still doesn't explain why the battery light comes on when restarting after the first start.
Thanks
Mike

[Baffler]

Originally Posted by Baffler

Hi, Mike, I'll need to double check the sequence but my understanding is, when the engine is started from cold, the glow plugs and the coolant heater plugs are continually working away in background...I think in 15 minute cycles. This may help explain no charge when up to temp. I'll get back to you on this.

Can I find where I've read the above...no chance! I can't find it in VIDA so must have been in the older version of VADIS or perhaps the Owners Manual. Do you have your Owners Manual to hand?


Not wishing to go down the rabbit hole either, Mike, so if you could go back to the beginning once more. When you found the glow plug lead arcing against the head did you inspect and test all the fuses in the engine bay fuse box, there's a large 80amp fellow in there, and is the copper strip/fuse intact under the plastic cover in the pre-heat relay located to the front of the ECU housing?

You appear pretty well versed in the area, much better than I, but are you 100% certain the replacement regulator is correct for your alternator? There is a 110amp and 120amp alternator depending on region. The 120amp, I believe, has some additional harness.

And how good is your battery? These can produce strange electrical behaviour when a battery is weak or low.

[mikebo]

Hi Liam, apologies for the delay in replying, a combination of being pulled in several directions and lousy weather. No worries for not being able to find the information, it's been often my experience to only find what I've been looking for 3 weeks later when looking for something entirely different. Extremely frustrating.
Confirm that all fuses are in good condition.
I saw that the D+ wire from the alternator goes to connector 24/15 which is the part you identified as having the pre-heat relay and the large copper fuse/link.
After making sure all connections were clean and tight I started and stopped the engine, the battery light behaved correctly On restarting 3 times in succession the battery light behaved correctly. My hopes were rising. 4th restart and the battery light came on. Damn (or something similar!).
Going to start changing bits.
Confirm it's a 120A alternator and the regulator was for 120A.
What document can I use to identify the parts? I've ordered the Audi Haynes manual for the engine (read that somewhere on this forum iirc) but don't know from where to get the rest.
Thanks
Mike