ABS warning light only shows when lights are on! W124

[peter01443]

Weird or what?

ABS doesn't work on 1990 200 Carb. But warning light goes out on start but lights up when the light switch is on!

Is this a clue to what is wrong?

Help

 

[television]

Weird or what?

ABS doesn't work on 1990 200 Carb. But warning light goes out on start but lights up when the light switch is on!

Is this a clue to what is wrong?

Help

Hi Peter, just trying to think about this, on key 2 (ign) the ABS light is on, you start the car and it goes off,so far all correct, but when you turn the lights on the ABS lamp comes on again is this what is happening.

Malcolm

 

[peter01443]

Yes

That is exactly it. The ABS doesn't work, and hasn't for a couple of uears, but this MOT it has failed on ABS, although passed before. I guess it's a result of the new computerised MOT system.

So now I have to get ABS fixed so am hoping that this odd light scenario miht give me a clue as to where to look.

 

[television]

Yes

That is exactly it. The ABS doesn't work, and hasn't for a couple of uears, but this MOT it has failed on ABS, although passed before. I guess it's a result of the new computerised MOT system.

So now I have to get ABS fixed so am hoping that this odd light scenario miht give me a clue as to where to look.

do you think that the wiring has been altered to try and cover up before you bought the car.

If you search the forums we had one in the autum where one of the main ABS pump wire had come out,and it was laying behind the unit. With the engine running there must be 12 volt on the ABS pump.

do not know what help I can give, I may have the wiring of the unit.

Anyone here know if the wiring diagram is in the Haynes book.

Malcolm

 

[peter01443]

Just checked OVP fuse - BLOWN!

Replaced it and for the first time in 3 years the ABS is WORKING!!!

Warning light still coming on with ligts though. Should I wait a while, will it take a while to reset itself?

 

[anyweb]

if the abs warning light is coming on then chances are the abs sensors are fault/dirty or some other failure such as a corroded wire which may have led to the ovp fuse blowing in the first place

time to take off your wheels and checkout the abs sensors/wires

cheers
anyweb

 

[kth286]

It's an indication that the battery and/or charging system is faulty, because there must be a minimum voltage for ABS to operate.

The ABS is designed to automatically de-activate when the threshold voltage is not reached. The brakes will still work of course.

So take car for run to get the battery charged up and see if fault disappears.

If fault disappears then likely you have a low voltage problem.

 

[television]

Just checked OVP fuse - BLOWN!

Replaced it and for the first time in 3 years the ABS is WORKING!!!

Warning light still coming on with ligts though. Should I wait a while, will it take a while to reset itself?

The ABS lamp is operated by the high presure pump,so nothing wrong there, someone must have altered the wiring under the dash at some point to hide the problem.

Malcolm

 

[124coupe]

Just to recap:

The ABS now works (since OVP fus replaced)
The warning light behaves now exactly as it did before the OVP fuse replaced.

Is that correct?

If so, I would pull the speedo binnacle - someone MAY have put the warning lights back in the wrong holes..... not unknown! (and therefore you might be seeing the "blown bulb" warning - for example - through the wrong decal).

 

[kth286]

peter01443

So, just to recap also:

When you put the headlights on, and the ABS light also comes on, do the brakes work in the ABS mode, ie. can you feel the pulsations when you push the pedal hard and try and lock the brakes. ??????????

 

[television]

Some one has got at this,its not a possible fault, unless tracks blown on cluster PCB.

malcolm

 

[peter01443]

Current situation is that the OVP fuse has been replaced and the ABS works all the time (lights on and off).

BUT

The warning light comes on within a second or so of the light switch been turned on (side or head).

What circuits do you think I shuld check, what in the lighting circuit could effect the ABS warning lamp.

I will be removing the dash tomorrow to see if there has been any tinkering in there!

 

[television]

Current situation is that the OVP fuse has been replaced and the ABS works all the time (lights on and off).

BUT

The warning light comes on within a second or so of the light switch been turned on (side or head).

What circuits do you think I shuld check, what in the lighting circuit could effect the ABS warning lamp.

I will be removing the dash tomorrow to see if there has been any tinkering in there!

If the tracks on the PCB have lost a ground point,this could account for the lamp comming on with the lights as it could grounding via the lights.

Any green spots on the PCB normally indicate a break.

Malcolm

 

[124coupe]

Looking at the wiring schematic, there should be no link between lights on/off and the ABS warning light.

ABS light is triggered by <10V delivered to the ABS unit by the OVP or by ABS failure.

Switching the lights on could (?) drop the voltage below the trigger if there is a battery or charging fault??

The warning lights on the RHS of the binnacle (on my car) are on flyleads (left to right washer fluid, light bulb fail, ABS, SRS).

I do wonder if someone transposed the light fail and ABS warning bulbs.....are all the lighting bulbs OK (front and rear inc sidelights?). Also the light warning triggers if bulbs of unequal wattage are fitted in each "pair" and if the bulb or holder contacts are dirty or ill fitting (changing the resistance) - this is common on these old cars......

The flyleads have little paper labels corresponding to the hole number they should be in....

 

[television]

Looking at the wiring schematic, there should be no link between lights on/off and the ABS warning light.

ABS light is triggered by <10V delivered to the ABS unit by the OVP or by ABS failure.

Switching the lights on could (?) drop the voltage below the trigger if there is a battery or charging fault??

The warning lights on the RHS of the binnacle (on my car) are on flyleads (left to right washer fluid, light bulb fail, ABS, SRS).

I do wonder if someone transposed the light fail and ABS warning bulbs.....are all the lighting bulbs OK (front and rear inc sidelights?). Also the light warning triggers if bulbs of unequal wattage are fitted in each "pair" and if the bulb or holder contacts are dirty or ill fitting (changing the resistance) - this is common on these old cars......

The flyleads have little paper labels corresponding to the hole number they should be in....

If these lamps are on fly leads then the chances are that the lamp failure bulb is in the ABS hole.

malcolm

 

[124coupe]

Instrument pod is a friction fit and can be pulled using two tools made from a coat hanger.

Bend over approx 5mm at the end and insert this "hook" at the top of the vertical part of each side edge and then rotate into the cluster. Pull both sides equally being careful not to slip and scratch the binnacle.

Release the speedo cable as soon as you can reach it (unscrew knurled nut) or you will kink it and suffer from an oscillating speedo needle at low speed!

Worth replacing the speedo etc illumination bulbs while you are in there as the old ones get dim (match the wattage to avoid melting the reflectors).

 

[124coupe]

Malcolm just for reference on the W124, the warning lamps on the left are part of a single-replacement PCB unit with a 15 way multi connector and the ones on the right (wash fluid/light fail/ABS/SRS/ASR) are flyleads. At least they are in 1995!

 

[television]

Malcolm just for reference on the W124, the warning lamps on the left are part of a single-replacement PCB unit with a 15 way multi connector and the ones on the right (wash fluid/light fail/ABS/SRS/ASR) are flyleads. At least they are in 1995!

Thank you i will remember that.

malcolm

 

[peter01443]

This is a mine of information - I sall be busy tomorrow - gentlemen, thank you.

 

[peter01443]

Just to put the matter to rest.

The ABS worked immediately the OVP fuse was replaced - thanks gents.

Some eager little beaver, having failed to fix the faulty ABS had taken out the dash, removed the ABS lamp and put the bulb failure holder in the ABS socket. Therefore to satisfy MOT, light comes on with ignition and goes out when the car starts. Hey presto!

But why did it light when the lights came on - it would only come on if there was a bulb failure - and there wasn't!!! I still dont know, and don't care, it's passed the MOT.

Once again, thanks for all the advice.