Car electronics died while driving

This morning on my way to work, I had to make a sudden stop. About a mile later, my dash lights began to dim, the ABS light came on, then the airbag light, then the radio cut out, and finally all the lights died as I parked. The battery died as well and the car could not restart.

Before this there have been no indications of a bad battery or alternator and I've had strong starts, even in the cold weather (it's been below freezing all week) and the serpentine belt is fine. Has something come disconnected? Would the shock of a sudden stop cause something to fail so suddenly?

Edit: I took a look at the 150A fuse and it's not blown.

I would get a jump start and then get a volt meter on your battery. Sounds like a dead alternator to me

If the alternator died would it be so sudden? Is it possible that just the voltage regulator failed?

I have noticed that when I removed the alternator completely from my spare ALH car the battery light did not illuminate after starting it to move it around.. kinda odd but I guess that's how it works on these cars so if the trigger wire got broken/disconnected from the alternator it may not have illuminated the light.

Thanks. I'm definitely leaning toward a connection issue since there wasn't any indication that the unit itself was failing. My battery/alternator light also did not come on. I think I'll replace the voltage regulator and hopefully that will solve the problem.

steve6 said:

I have noticed that when I removed the alternator completely from my spare ALH car the battery light did not illuminate after starting it to move it around.. kinda odd but I guess that's how it works on these cars so if the trigger wire got broken/disconnected from the alternator it may not have illuminated the light.

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The light is turned on through the regulator detecting something wrong.
I never trusted the light to indicate a problem.

stikshift said:

Thanks. I'm definitely leaning toward a connection issue since there wasn't any indication that the unit itself was failing. My battery/alternator light also did not come on. I think I'll replace the voltage regulator and hopefully that will solve the problem.

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Before throwing money at it guessing charge the battery and check the voltage:
Key off - battery voltage 12.6V is full charged.
Running should be at least 14 V iIrc
Does the alternator light come on with the key on & car not started?

Start it up, turn on all accessories (headlights/heat/radio) and disconnect the battery; if the alternator cant keep the car running it'll die again.. which means your car was running off battery power largely until it could not keep up anymore.. the battery is only used for starting, then the alternator should take care of the rest ontop of replacing the charge in the battery from the start.

If the battery isn't charging isn't it definitively the alternator? The battery is less than a year old and has been strong starting the car, even after sitting.

Batteries occasionally fail prematurely usually from defect or certain types of alternator failure.
But you can sort out whether your battery is good.
Likely alternator or connections. Alternator pulleys are trouble, but I don't know that that affects their ability to charge.

power relay 109 could be bad, search "relay 109"

Bit of an update; I was able to start the car without a jump, although it was very weak (it was sitting all day and it had warmed up a bit since this morning which probably helped). Drove home without issue with everything off and the gauges were displaying info properly. Once I parked, I shut the car off and the battery was too weak to start the car again, even with a warm engine. So it definitely is not charging.

wonneber said:

...
Does the alternator light come on with the key on & car not started?

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The light does not come on, but every other idiot light does

jayb79 said:

power relay 109 could be bad, search "relay 109"

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Doesn't sound like the same issue. All the power functions work, even with the weak battery. In fact, the car was pretty much normal.

Your battery would have to be a massive current sink for it to kill the car while it was driving; jump it again and follow the instructions I provided earlier.. Last time I had a bad alternator it could keep the engine running until it got dark and I turned on the headlights, then it put that load on the battery and it didnt make the long trip home; it shutoff on me on the turnpike..

Jumped it back alive, disconnected the battery and it was still running.. then I turned on the headlights and it was like I hit a kill switch.. the alternator could not recharge the battery or provide enough amps to do more than keep the engine going.

You can take the alternator out and most local automotive stores can put it on a rig and test its output for confirmation before you start throwing money at it.

Alternators are pretty cheap though. Had a similar problem with I first bought my Golf. Aside from the battery being bad, it wasn't charging on me either. Replaced the alternator and put on a new accessory belt/tensioner - RockAuto had the continental belt kit for under 60 bucks and a remanufacturered alternator (I think I got the 120A Bosch or Valeo, which even had a VW logo on the regulator) for about $120 or so. Haven't had any problems since, but YMMV.

I would first check for bad connections between the alternator and the battery; as well ast the fuses on top of the battery.

JB05 said:

I would first check for bad connections between the alternator and the battery; as well ast the fuses on top of the battery.

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The fuse is good. However I'm reading that the connection from the alternator to the cluster (the blue wire?) can fray and cause these faults. Where does it run?

Just track it from the engine compartment.
Check all your fuses.

So this has turned into a cruel joke...



The outer insulation of the harness from the voltage regulator cut the lead to the ECU. With no ground, there was no excitation, so no regulation. I'll get around to splicing the wire on Sunday and I will report back.

Failed wiring on a MKIV? Say it ain't so!

As time goes by it will become standard practice to always look over the wiring if there's any problem that could be associated with electrical issues.

Spliced the wire back and still no battery light. I jumped the D+ terminal and verified that the light does work, so now I'm back to the voltage regulator. Is it possible that because the lead to the ECU broke that it caused the regulator to overcharge and fail open?

stikshift said:

Spliced the wire back and still no battery light. I jumped the D+ terminal and verified that the light does work, so now I'm back to the voltage regulator. Is it possible that because the lead to the ECU broke that it caused the regulator to overcharge and fail open?

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I would think its possible.
Without a ground the regulator thinks there's low voltage and turns the alternator on.

A final update...

The regulator was in awful condition. The contacts and heat sinks were very corroded and the brushes were very worn. I guess losing the lead to the ECU was the final straw. Dropped the new regulator in and everything is back to normal.




However, it's the original alternator! (regulator was dated Feb '02, alternator dated Sep '02) So I suppose 14 years and 266k miles isn't half bad.

Excellent work!

Thanks! I wanted to make sure everything was documented in case someone else in the future has the same issue.