1996 850 T5 ABS fault, strange.

Dec 2nd, 2005, 18:07

I have done a search on this and used the knowledge gained to try and sort this out but to no avail. here are the symptoms:

The ABS light only comes on under hard or aggressive acceleration but never under braking or if the car is driven normally. It started a few weeks ago and as long as the car is driven normally it is fine. I have tried swapping ECU’s with a friends 96 T5 due to the notorious dry joint fault on the pins inside the ECU, when I did this I could see mine had already had the repair. The new ECU made no difference. The sensors have been checked with a meter and the front nearside one replaced, again no difference. The only OBDII tool I have will not communicate with Volvos so was of no help when I left the light on and plugged it in. The light resets whenever I start the car. Wierd one this I know, any ideas? thanks in advance.

bigandquick · Dec 3rd, 2005, 00:27

Yes, here's an idea. Turn off the TRACS system and try your harsh acceleration again. Does the ABS light still illuminate?
Unlike other more refined systems, the TRACS on the 850 does not control wheelspin by reducing power to the wheels, rather by utilising the ABS system to slow the wheelspin, or that's what I've been led to believe. That's why the TRACS system on them is not particularly effective. Chance now to test the theory.
So if the ABS light doesn't illuminate when the TRACS is off, chances are that is what is causing it. That said, the ABS light shouldn't come on during wheelspin, so there probably is a problem of some sort in the ABS side of things.

Dec 3rd, 2005, 09:16

thanks tim but the car does not have TRACS!

Chris_Rogers · Dec 3rd, 2005, 20:03

Suggest checking the each of gear-shaped sensor rotors and the sensor elements for dirt and to make sure the fixings are secure.

If that fails look for a crack in the rotor this may allow the rotor to move on the shaft and give false speed readings to the ABS ECU.

It would make it easier to have any fault codes read first, you can get a fault code reader here:

http://www.onboarddiagnostics.co.uk/volfcr/index.htm

Dec 4th, 2005, 08:43

thanks ,will do.

Dec 9th, 2005, 16:57

Just thought I would let you all know what the fault was in the end. It was the brake fluid pressure sensor mounted in the underside of the servo. Wierd one and the garage had never had that before. Took them a while to find and the only way to recreate the fault was to drive the car so a bit of a pain int he a**e!

Dec 2nd, 2005, 18:07	#1
jizm Guest Location:	1996 850 T5 ABS fault, strange. I have done a search on this and used the knowledge gained to try and sort this out but to no avail. here are the symptoms: The ABS light only comes on under hard or aggressive acceleration but never under braking or if the car is driven normally. It started a few weeks ago and as long as the car is driven normally it is fine. I have tried swapping ECU’s with a friends 96 T5 due to the notorious dry joint fault on the pins inside the ECU, when I did this I could see mine had already had the repair. The new ECU made no difference. The sensors have been checked with a meter and the front nearside one replaced, again no difference. The only OBDII tool I have will not communicate with Volvos so was of no help when I left the light on and plugged it in. The light resets whenever I start the car. Wierd one this I know, any ideas? thanks in advance.

Dec 3rd, 2005, 00:27	#2
bigandquick Premier Member Last Online: May 15th, 2024 14:37 Join Date: Dec 2003 Location: Cambridge	RE: 1996 850 T5 ABS fault, strange. Yes, here's an idea. Turn off the TRACS system and try your harsh acceleration again. Does the ABS light still illuminate? Unlike other more refined systems, the TRACS on the 850 does not control wheelspin by reducing power to the wheels, rather by utilising the ABS system to slow the wheelspin, or that's what I've been led to believe. That's why the TRACS system on them is not particularly effective. Chance now to test the theory. So if the ABS light doesn't illuminate when the TRACS is off, chances are that is what is causing it. That said, the ABS light shouldn't come on during wheelspin, so there probably is a problem of some sort in the ABS side of things. __________________ Tim '16 XC60 SE Lux Nav

Dec 3rd, 2005, 09:16	#3
jizm Guest Location:	RE: 1996 850 T5 ABS fault, strange. thanks tim but the car does not have TRACS!

Dec 3rd, 2005, 20:03	#4
Chris_Rogers VOC Member Last Online: Apr 10th, 2017 16:55 Join Date: Jan 1970 Location: South Kent Coast	RE: 1996 850 T5 ABS fault, strange. Suggest checking the each of gear-shaped sensor rotors and the sensor elements for dirt and to make sure the fixings are secure. If that fails look for a crack in the rotor this may allow the rotor to move on the shaft and give false speed readings to the ABS ECU. It would make it easier to have any fault codes read first, you can get a fault code reader here: http://www.onboarddiagnostics.co.uk/volfcr/index.htm

Dec 4th, 2005, 08:43	#5
jizm Guest Location:	RE: 1996 850 T5 ABS fault, strange. thanks ,will do.

Dec 9th, 2005, 16:57	#6
jizm Guest Location:	RE: 1996 850 T5 ABS fault, strange. Just thought I would let you all know what the fault was in the end. It was the brake fluid pressure sensor mounted in the underside of the servo. Wierd one and the garage had never had that before. Took them a while to find and the only way to recreate the fault was to drive the car so a bit of a pain int he a**e!

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