ABS Light ON But VCDS Shows No Fault Codes

mike

Veteran Member
Joined
Sep 28, 1999
Location
New England
TDI
2015 Q5 Tdi, RIP 2003 Jetta GLS 5sp
ABS light randomly comes on and stays on. VAG Com / VCDS shows no fault codes under Engine, Instrument Panel or ABS Systems. But Meas block 3 under ABS shows fluctuating On/OFF. Car runs great except it beeps when ABS light comes on randomly about 5-10 min into drive then ABS light stays on for duration of the journey.

Any advice on how to reset that ABS light appreciated.

2003 A4 GLS ~138kmi
 

MOGolf

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Joined
Jun 27, 2001
Location
underneath something
TDI
2001 Golf GLS TDI Reflex silver, rough road suspension and steel skid plate, 2004 Passat Variant, Candy White, rough road suspension and geared balanced shaft module, and much, much more. 2016 LR RR HSE TD6, 2019 Jaguar I-PACE
I suspect a rear brake is dragging. This will cause the wheel to turn slower than expected and cause these symptoms.
Or something is causing a rear sensor to not give the expected number of pulses.
 

Powder Hound

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Joined
Oct 25, 1999
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Under a Bridge, Crestview, FL, USA
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'00 Golf 4dr White 5sp, '02 Jettachero 5sp, Wife's '03 NB Platinum Gray auto(!)
I've had an abs light on twice. Once in the Golf after an emissions test, but it calmed down during the drive home from the testing station.

The other was lately after the brakes were worked on in the Jetta. A scan showed the left rear sensor is intermittent. An examination of that sensor shows one that is corroding and small chunks are breaking off. I've ordered new rear sensors.

A scan of the system should show the stored codes. You really need a VCDS for diagnosis.
 

mike

Veteran Member
Joined
Sep 28, 1999
Location
New England
TDI
2015 Q5 Tdi, RIP 2003 Jetta GLS 5sp
abs light

Please share your thinking why the rear wheel sensor?

My VCDS (RossTEch) doesn't find any fault code for rear wheel sensor?
What's confusing is it shows no fault codes whatsoever but that ABS light is on.
 

MOGolf

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Joined
Jun 27, 2001
Location
underneath something
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2001 Golf GLS TDI Reflex silver, rough road suspension and steel skid plate, 2004 Passat Variant, Candy White, rough road suspension and geared balanced shaft module, and much, much more. 2016 LR RR HSE TD6, 2019 Jaguar I-PACE
If the sensor isn't sending the proper number of pulses expected, then the ABS thinks the wheel isn't turning properly and you get the ABS light. Just set the parking brake, drive off with it dragging and you can get the ABS light on. Release the parking brake, turn the car off and on, drive off again and the light is off. It isn't finding an open circuit or a grounded circuit. It is finding a difference in number of expected pulses.

You can only monitor this at less than 20 kmh. Above that it stops responding. Monitor measuring block group 002. Watch the values in blocks 1 and 2. They should not be more than 6 kmh different. Watch values in 3 and 4. They should not be more than 2 kmh different.

Other causes are a damaged rotor or excessive air gap between a sensor and the sensor wheel on the front or ribbs on the rears.
 

mike

Veteran Member
Joined
Sep 28, 1999
Location
New England
TDI
2015 Q5 Tdi, RIP 2003 Jetta GLS 5sp
Now Always On

MOGolf said:
If the sensor isn't sending the proper number of pulses expected, then the ABS thinks the wheel isn't turning properly and you get the ABS light. Just set the parking brake, drive off with it dragging and you can get the ABS light on. Release the parking brake, turn the car off and on, drive off again and the light is off. It isn't finding an open circuit or a grounded circuit. It is finding a difference in number of expected pulses.

You can only monitor this at less than 20 kmh. Above that it stops responding. Monitor measuring block group 002. Watch the values in blocks 1 and 2. They should not be more than 6 kmh different. Watch values in 3 and 4. They should not be more than 2 kmh different.

Other causes are a damaged rotor or excessive air gap between a sensor and the sensor wheel on the front or ribbs on the rears.

Just to clarify the instrument light in question is the one with the circle and a band on the left and right kinda resembles a drum brake like this (0). Now this light is always on. As soon as I turn the key the others go out but this stays on as I drive off.

VW Vortex seems to suggest lots of problems with ABS and a possible recall. Anyone know?
 

fitzski

Veteran Member
Joined
Oct 13, 2004
Location
Ottawa
TDI
Uh... hmm... Well, none...
What you're describing is the brake pad wear indicator, from a sensor on the left front wheel. The warning lamp is the top centre icon in the middle of this cluster:


The ABS warning says "ABS"... they are separate.
 
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