Voltage issues

Invertigo

Invertigo

Invertigo

Associate
Joined
19 Sep 2010
Posts
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Location
The North
Morning all,

Hoping someone with a bit of car electrical knowledge might be able to help me here.

Basically, I've had a few moments when driving flat out ie down a slip road or something, and when the engine reaches high rpm (6k plus) I get a trio of warning lights for ABS DSC and TCS.

Did a code read and the error was 5d97 and 5df7, which equate to
Dynamic Stability Control (DSC) sensor. Voltage supply
And
5DF7 System voltage greater then 18 volts

At the same time most recent, there was a high load on the electrics, with heated seat, climate control, radio, lights and wipers on.

I've recently changed the voltage regulator as I thought that might be the problem. However on the way home yesterday I monitored the voltage all the way and had a constant 14v when driving, +-0.2v.

The car also reads the engine off voltage as 12.3v which I believe is on the low side? I've never had any issues with starting the car so the CCA is clearly not deteriorated severely, but perhaps the constant output could be?

The other consideration I had was a possible bad ground, does this sound likely?

Any help would be fantastic, and if any more tests can be done to further narrow down the culprit please let me know.

Edit: monitored the voltage on a drive this morning. Running engine to redline with HVA blower, lights and radio on and steady 14v.

Turn heated seats on and try again, spikes up to 18v.

So realistically, would this point to a bad battery/alternator? Can't see it being ground when it seems dependant on electrical load, unless it's a bad ground on heated seats?
 
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What car is this on?

It sounds like the alternator is playing up as that is what is generating the power. The battery sounds a little low but that wouldn't give you a higher voltage under load. Might be worth checking the ground cable from the body/battery to the engine, if this is playing up the alternators reference to ground(0v) would be off.

When you changed the voltage regulator is it part of the diode/brush pack on the alternator?
 
Tried with a replacement battery today and no change. Also checked battery and engine grounds, both perfect. Reseated them and cleaned them off as a precaution but no change.

Next step is to try a replacement alternator I guess, can order one from ECP at least and return if it doesn't solve the issues. I do however find it funny that a Bosch OEM one can be had from Germany for less than a Lucas branded one from ECP, including discount and core return.

The common issue, however, seems to be that it only happens when heated seats are turned on. Could this point to a ground fault in the seat circuit?
 
It's happening when the heated seats are on because of the high load on the alternator. Change that first if you have already checked the engine ground.
 
Dandle said:
It's happening when the heated seats are on because of the high load on the alternator. Change that first if you have already checked the engine ground.
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Planned for the weekend, however speaking to the previous owner, the current alternator is only around 1 year old. Surely it couldn't be gone bad so fast?
 
Invertigo said:
Planned for the weekend, however speaking to the previous owner, the current alternator is only around 1 year old. Surely it couldn't be gone bad so fast?
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If the alternator is that new you could just replace the voltage regulator in it which won't be very expensive.
 
I've had TCS, ABS and DCS occasionally flash up all together in a Mazda 6 MPS - was a flaky ABS sensor. I didn't get an ABS error code for this from any of the cheapo £10-20 OBD2 readers I tried, but the garage's better reader spotted it.
 
bledd said:
What car is it?

Tried the owners forums?
Click to expand...

BMW Z4, and yes I have topics on a couple of them too!

Dandle said:
If the alternator is that new you could just replace the voltage regulator in it which won't be very expensive.
Click to expand...

Already tried, no difference.

DereksDontRun said:
I've had TCS, ABS and DCS occasionally flash up all together in a Mazda 6 MPS - was a flaky ABS sensor. I didn't get an ABS error code for this from any of the cheapo £10-20 OBD2 readers I tried, but the garage's better reader spotted it.
Click to expand...

This has been checked with dealer grade software. INPA and DIS both show the same two errors, 5d97 and 5df7.
Not sure this would explain the voltage jumping up to 18v either?
 
I had a similar issue where it was the reluctor ring causing issues, this was also causing the car to drop revs as the ABS was starting to kick in, very annoying! (This was on an BMW E90 if that helps)
 
Well I have an alternator in the boot to try tomorrow, I both hope it does fix it and that it's something else cheaper, but hey ho!

Alternator was replaced previously due to not charging the battery. It was however a remanufactured unit so perhaps something has failed? I'll test it with my borrowed known good replacement anyway and if that solves the issue I'll get a new Bosch unit from Germany, much cheaper than here.
 
So, the previously replaced alternator is a 110 amp output.

Factory fit is 120 amp output.

Makes sense it wasn't able to handle full load on the electrics and engine then, no?

My test fit known working alternator did a perfect job, no voltage spike and never went over 14.1v measured at OBD, and never went over 14.5v at the alternator measured with a multimeter.

New Bosch part ordered from Germany, hopefully be the end of the issue. Same price as a rebuilt unit from ECP so it's a no brainer.
 
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