ABS Fault, but what's wrong?

[Heddy]

Hi all, I've read a few posts and if I list the symptoms maybe I can pin down this problem. I have 'ABS Fault' (top display) briefly appearing, ABS light constant, have no speedo reading and the fuel gauge is up and down constantly, showing low fuel warning on and off even though I have over 1/4 tank. Your thoughts please.
Cheers.

[klarzy]

Hi all, I've read a few posts and if I list the symptoms maybe I can pin down this problem. I have 'ABS Fault' (top display) briefly appearing, ABS light constant, have no speedo reading and the fuel gauge is up and down constantly, showing low fuel warning on and off even though I have over 1/4 tank. Your thoughts please.
Cheers.

The ABS light and speedo point to an ABS sensor fault, the fuel issue could be a bad sender or a short...

[spudtrooper37]

The o/s/f wheel. Could be the abs sensor, bearing or loose wire. I had same symptoms. Because that sensor controls the speedo, so if that is not working then the fuel computer does not get a correct reading, hence the fuel gauge gets affected. Hope it's just a loose connection.

[Heddy]

Thanks for the replies.The ABS light has been on intermittent for a few days, disappearing when the ignition was switched off and back on. The speedo only ceased to work tonight, along with the erratic fuel gauge. Will check the sensor. :}

[klarzy]

Thanks for the replies.The ABS light has been on intermittent for a few days, disappearing when the ignition was switched off and back on. The speedo only ceased to work tonight, along with the erratic fuel gauge. Will check the sensor. :}

It may also be the reluctor ring in the wheel bearing braking up... the ABS sensor reads off of this...

[Heddy]

It may also be the reluctor ring in the wheel bearing braking up... the ABS sensor reads off of this...

Yes, I'm just familiarising myself with it, new bearings were fitted last month.

[klarzy]

Yes, I'm just familiarising myself with it, new bearings were fitted last month.

Well you have to remove the abs sensor from the hub to get the bearing past it, they are usually corroded in and need to be destroyed to remove them.

If not the sensor may have been damaged or the wiring stressed, check the plug up in the inner wing where the sensor joins the loom and clean the connections.

A new sensor is between 15 and 60 quid dependent on where you buy, I got the 15 quid variety from ebay and it has been fine for 9 months...

[twowheelstony]

my diesel does the same if i turn the key to start too quick after switching ignition on .
try switch to on , leave till lights go out etc then start it

[Heddy]

Should have updated this, it was the ABS sensor connecting plug. Once pulled apart and re connected all has been fine.:}

[cookie62]

MG ZT CDTi 2003 saloon
Pleased you got yours fixed! Having prob with ABS warning light on too.
Having read all the posts I can find, still not sure what to do next. ABS light came on last Sunday (3rd May) after driving through heavy rain, parking and leaving vehicle for two hours. Started after two hours, ABS light on and warning message briefly. Recently changed o/s/r caliper because it had seized and heated up disc, hub and wheel (couldn't touch it, it was very hot). Bled that caliper once only and went back to working on my van. (£700+ worth of repairs for MOT!) Drove the car for next three weeks after this with no problem. Then as described above. Suspected o/s/r abs sensor because of being cooked and sure enough it's melted in the hole in the hub. Bought replacement from DMGR spares and plugged in but still light on. Tried it on the other two (n/s/l and n/s/f - speedo still works so didn't try it on that one) still the light stays on. Disconnected battery for 2 hours while looking at connector on ABS pump/ecu, no visible signs of any cable breakage anywhere. Reconnected battery, still abs light on. Also tested power to sensors on n/s/f and o/s/r with ignition on and got a reading 0.6v. Any suggestions please on what to look at next? I live about 50 mins away from Trikey in North Lincolnshire. And before I forget, many many thanks to you all for such a lively informative and kind place to visit-spent many hours reading posts and solved many problems without having to ask, but stumped on this one. Best regards to you all, James.

[RodgerD]

The ABS sensor has two wires, one being a positive feed at battery volts and a return that switches between 0.6 volts and 1.6 volts, it switches 48 times per wheel revolution. The bearing acts as a reluctor ring and induces a hall effect in the sensor.

Firstly you need to check there is a +ve feed to the sensor. Secondly you need to check that it switches 48 times/ revolution. I put the tyre valve at 12 noon and with a multimeter's +ve lead on the output (signal wire) and the multimeter -ve on the car body. I then slowly turn the wheel one revolution (jack the wheel up first), counting the number of times the volts switch from 0.6 to 1.6 volts.

If less than 48 switches, then either the bearing is defective or the air gap between the sensor and bearing is too great. If no switches at all, then more likely its the sensor.

[David Lawrence]

MG ZT CDTi 2003 saloon
Pleased you got yours fixed! Having prob with ABS warning light on too.
Having read all the posts I can find, still not sure what to do next. ABS light came on last Sunday (3rd May) after driving through heavy rain, parking and leaving vehicle for two hours. Started after two hours, ABS light on and warning message briefly. Recently changed o/s/r caliper because it had seized and heated up disc, hub and wheel (couldn't touch it, it was very hot). Bled that caliper once only and went back to working on my van. (£700+ worth of repairs for MOT!) Drove the car for next three weeks after this with no problem. Then as described above. Suspected o/s/r abs sensor because of being cooked and sure enough it's melted in the hole in the hub. Bought replacement from DMGR spares and plugged in but still light on. Tried it on the other two (n/s/l and n/s/f - speedo still works so didn't try it on that one) still the light stays on. Disconnected battery for 2 hours while looking at connector on ABS pump/ecu, no visible signs of any cable breakage anywhere. Reconnected battery, still abs light on. Also tested power to sensors on n/s/f and o/s/r with ignition on and got a reading 0.6v. Any suggestions please on what to look at next? I live about 50 mins away from Trikey in North Lincolnshire. And before I forget, many many thanks to you all for such a lively informative and kind place to visit-spent many hours reading posts and solved many problems without having to ask, but stumped on this one. Best regards to you all, James.



What state is the backplate on your rear brakes like? When my abs came on it was because during work on the handbrake, rust had dislodged, then got trapped between the sensor and the bearing face, and damaged both. The bearing ring had a groove worn in it. You mention your sensors, have you inspected the ring on the inside face that the sensor picks up from, and while you have the bearing off to check it, take a chance to wire brush off any rust and spray with rust convertor.

[cookie62]

Thank you Heddy, Rodger and David, will follow your suggestions and report back. Maybe take me a week now to to see what's up 'cos I have two hospital appointments and work to fit in before next weekend! The backplate on the o/s/r does appear a bit frilly so quite likely that I may have dislodged some rust-we shall see. Many thanks for your valuable help.
James.

[cookie62]

Well here we are with another week gone and so has my abs light! After posting last week (10th May) all I had done was check around for any broken wires etc, removed battery and tray to check the pump and ECU connector etc. I have'nt as yet followed the suggestions from David, Heddy and Rodger-here's why: On Monday I drove 40 miles with the light on (hospital appointment), left the car for 45 mins and after travelling 100yards of the return journey the light went out! In the evening of that day did a 21 mile journey light on again outward bound and off on the journey back home. Weather very warm and dry. Weds of this week did another long journey 170 miles, light off both there and back and has stayed off ever since! I'm quite sure I haven't done anything to cure this but for the moment I'm relieved. If it starts misbehaving again I'll follow the suggestions and start digging deeper.
James.