Intermittent brake warning light, engine juddering error - off / on and problem clears

Q

quantumtokoloshi

Member
United-Kingdom
1.4 petrol has developed an intermittent brake warning light, dashboard lights up up like a Christmas tree style error. When coming off the throttle.

You'll be driving along fine, as you come off the throttle, dashboard lights up, red brake warning light, and engine judders. Turn on and off, and run perfectly again. Only other symptom we have noticed just before the error occurs, coming on and off the throttle is not smooth, has a flat spot between zero throttle and applied throttle as the engine hesitates, then goes, once you do the reset, engine runs smoothly again.

Battery is okay, charged it fully, no other issues, car runs well, pulls well, until this oddity happens. My guess is possibly throttle body, ABS and/ or sensor or maybe ECU, anyone has something similar?
 
Did you replace anything recently or been in engine bay doing some work?
 
The first thing to do would be to get a VCDS scan, the stored codes should give pointers as to what’s causing the problem
 
quantumtokoloshi said:
1.4 petrol has developed an intermittent brake warning light, dashboard lights up up like a Christmas tree style error. When coming off the throttle.

You'll be driving along fine, as you come off the throttle, dashboard lights up, red brake warning light, and engine judders. Turn on and off, and run perfectly again. Only other symptom we have noticed just before the error occurs, coming on and off the throttle is not smooth, has a flat spot betwen zero throttle and applied throttle as the engine hesitates, then goes, once you do the reset, engine runs smoothly again.

Battery is okay, charged it fully, no other issues, car runs well, pulls well, until this oddity happens. My guess is possibly throttle body, ABS and/ or sensor or maybe ECU, anyone has something similar?
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Sounds like Limp Mode. As @Indi says a scan will, very likely, tell you what's the cause.
Mac.
 
I had something similar. Check the brake light switch is correctly set, so it doesn’t come on with the lightest of touches on the pedal.
 
Do you get any crackling noise on the radio (AM stations in particular)? - that can be a sign that the brake switch is beginning to cause issues.

Our AUA has also experienced the limp / loss of throttle body control / all the lights coming on situation on a handful of occasions, mostly a calendar year ago when it was cold. The impression that I had based on common patterns of circumstances on a few occasions was that this was probably related to voltage getting to critical levels, with lights on, some time after starting, maybe battery not fully charged owing to short distance commute driving and then doing something like steering and braking at the same time. Sudden ping, lots of warning lights and erratic idling, probably caused by voltage dip making various ECUs get unhappy.

Solution to this (this year) has been reconditioning the battery on the CTEK every 2-3 days which has kept these events to a bare minimum, and I have a 110A alternator for the FSi that I'm going to get fitted when I have time to maybe give slightly more battery recharging effort.
 
Robin_Cox said:
Do you get any crackling noise on the radio (AM stations in particular)? - that can be a sign that the brake switch is beginning to cause issues.

Our AUA has also experienced the limp / loss of throttle body control / all the lights coming on situation on a handful of occasions, mostly a calendar year ago when it was cold. The impression that I had based on common patterns of circumstances on a few occasions was that this was probably related to voltage getting to critical levels, with lights on, some time after starting, maybe battery not fully charged owing to short distance commute driving and then doing something like steering and braking at the same time. Sudden ping, lots of warning lights and erratic idling, probably caused by voltage dip making various ECUs get unhappy.

Solution to this (this year) has been reconditioning the battery on the CTEK every 2-3 days which has kept these events to a bare minimum, and I have a 110A alternator for the FSi that I'm going to get fitted when I have time to maybe give slightly more battery recharging effort.
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I suspect the battery is the problem if it needs reconditioning every 2-3 days. Unless there’s other electrical faults causing a drain, or the current alternator is failing, then my money would be on a new battery having much more of an impact than a slightly uprated alternator
 
My VCDS is giving issues, won't connect, so will have to play with it to get the error messages. Thanks all for the helpful suggestions, please keep them coming.
 
quantumtokoloshi said:
My VCDS is giving issues, won't connect, so will have to play with it to get the error messages. Thanks all for the helpful suggestions, please keep them coming.
Click to expand...
That in itself seems possibly indicative of a larger problem, maybe a wiring issue or possibly ECU related maybe. I would be starting with solving that personally, as if something is wrong then the other issues you have described could well just be weird symptoms
 
Indi said:
I suspect the battery is the problem if it needs reconditioning every 2-3 days. Unless there’s other electrical faults causing a drain, or the current alternator is failing, then my money would be on a new battery having much more of an impact than a slightly uprated alternator
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My suspicion is on the alternator - at >205,000 miles old and there is a distant chirp (not the clutched pulley failure you get on the Tdi but possibly beginning to fail). Hence planned refurbed 110A one.}

Apologies to OP for thread swerve onto my own car.
 
Robin_Cox said:
Do you get any crackling noise on the radio (AM stations in particular)? - that can be a sign that the brake switch is beginning to cause issues.

Our AUA has also experienced the limp / loss of throttle body control / all the lights coming on situation on a handful of occasions, mostly a calendar year ago when it was cold. The impression that I had based on common patterns of circumstances on a few occasions was that this was probably related to voltage getting to critical levels, with lights on, some time after starting, maybe battery not fully charged owing to short distance commute driving and then doing something like steering and braking at the same time. Sudden ping, lots of warning lights and erratic idling, probably caused by voltage dip making various ECUs get unhappy.

Solution to this (this year) has been reconditioning the battery on the CTEK every 2-3 days which has kept these events to a bare minimum, and I have a 110A alternator for the FSi that I'm going to get fitted when I have time to maybe give slightly more battery recharging effort.
Click to expand...
I also thought battery, we had issues before with shorter journeys causing problems. I made sure it was properly charged, had it on the smart charger for a day or so, but this problem still happened, not voltage drain, as it starts with alacrity, I'll check the earthing points, as this may also be a possibility,
 
Indi said:
That in itself seems possibly indicative of a larger problem, maybe a wiring issue or possibly ECU related maybe. I would be starting with solving that personally, as if something is wrong then the other issues you have described could well just be weird symptoms
Click to expand...
Fair point, may need to swop out the ECU to see if it it a connection or a module issue.
 
Starting with alacrity is not a typical symptom of bad earth. On ours the earth needing to be cleaned manifested itself as a freshly charged recent battery turning over 2-3 times and then everything conking out without even sparking up (ie dashboard lights browned out).
 
quantumtokoloshi said:
I also thought battery, we had issues before with shorter journeys causing problems. I made sure it was properly charged, had it on the smart charger for a day or so, but this problem still happened, not voltage drain, as it starts with alacrity, I'll check the earthing points, as this may also be a possibility,
Click to expand...
If the battery is still suspect then I would leave it in the car for a few days and then check the voltage, then start the car and check the voltage again with the engine running, a knackered battery can appear charged on a smart charger but may not hold charge well
 
Indi said:
If the battery is still suspect then I would leave it in the car for a few days and then check the voltage, then start the car and check the voltage again with the engine running, a knackered battery can appear charged on a smart charger but may not hold charge well
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Good point, I have an older trickle charger, which I'll give it a few hours on and see.
 
quantumtokoloshi said:
Good point, I have an older trickle charger, which I'll give it a few hours on and see.
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I would charge it for a few hours, check the voltage, then check the voltage in a few days to see if it’s dropped
If it charges up to 13-14 volts, and is still good in a few days time then you can probably rule out the battery I think
 
Similar issues with the dash lighting up like a Christmas tree are usually related to power (was for me, and I’ve seen multiple similar cases from other users on here) so I would try and rule that out first, and then if power is all good then probably look at why VCDS won’t connect
 
PlasticMac said:
What is the error message exactly, when you plug vcds into the car?
Mac.
Click to expand...
Will not sync on protocol, same issue with my Foxwell scanner, will not accept any protocol, , sometimes will connect to kw 2000 protocol on the Foxwell scanner, reads extremely slowly, and will not clear DTCs.

VCDS works okay on my other VAG cars.
 
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