Asr, bas, then abs warnings

[BDE1V]

Ive a new fault on my W208 CLK regarding ASR, BAS then ABS Warnings.
I've had to replace the Brake Switch a few years ago which would give ASR & then BAS faults as soon as the brake pedal was touched after switch on.

I've had the brake pedal switch out & checked both it's switch contacts with an ohmeter & everything is fine regarding switch contacts.

This fault is different in that the ABS & the combined BAS,ASR Warning lights don't go out once the ignition is turned & the engine started. The Display then indicates the three faults in sequence.. I've never seen the ABS Light on before so i'm assuming the fault is related to this.. Battery voltage is normal & alternator charging ok, so nothing to do with low voltage etc.

Anyone know where the ABS Unit is located on this so model.

Any help would be appreciated

Regards

Brian

 

[BlackC55]

Just get the codes read to see what is causing it.

 

[nujon]

Before you spend any money, make sure the connections of the wheel sensors and the abs pump to the main harness are sqeaky clean and dry - if not, gently scrub with switch cleaner using a nylon brush (old toothbrush will do!) - all these devices are active digital and any corrosion-related resistance can set off the series of faults you describe

 

[BDE1V]

I was pulled over last night with brake lights on all the time, so either this is the fault or possibly I haven't put the switch back correctly, which is difficult because it just a straight fit with a 1/4 twist & it''s a firm fit.

However removing the switch with the wiring attached and with the switch plunger fully out the lights are on, push the plunger in & the lights go out.

Testing this with a DVM the heavier switch connections are the ones that switch the brake lights on on off...or at least trigger them on and off.

Looking at the mechanical mechanism & the switch position. the plunger must be depressed slightly when fitted so that the brake lights are off without the brake pedal depressed. Pressing the brake should fully extend the plunger & switch the lights on.

This isn't happening, so i can only assume the plunger end has worn or the switch internal spring/mechanism has worn.. I'll try & get another switch tommorrow & take it from there.

I still think the problem with ASR BAS & ABS is still there since depressing the plunger & starting the car still produces the same results

 

[BDE1V]

Just an update on this.. Received new brake switch, which cured my brake light issue, however i did notice they've changed the plunger length on this .
Anyway, connected PC & interface upto the 38pin connector to read fault codes & comes up with fault C1103 Right Rear Wheel Speed Sensor Open Circuit. Also repeats after clearing the fault.
Anyone know where the speed sensor wires run & the module they run into on w208 clk
I've an ASR Unit in the engine compartment, but can't seem to locate any ABS Unit

 

[andy27168]

Hi,
Have a check on the reluctor rings on the drive shaft as these seem to cause a lot of issues on the ABS system, if these are ok just replace the speed sensor, disconnect speed sensor and follow cable, which I believe will enter the boot space and will plug into the cars loom, this plug I believe is behind the rear seat on the boot floor under a plastic cover.

 

[BDE1V]

Cheers Andy,

I've just been under the car looking to see where speed sensors are, & managed to locate the large plastic cover.

There's 3 cables coming up from the rear of the car which plug into sockets.

The cables from the sockets then run off into the inside of the car.

Two of these cables look like the same type of connector whilst the third is different.

A good assumption is that 2 that look the same run to the left & right rear wheel sensors.

I've unplugged both of these & measured the resistance across the two pins at the connector.

The left side connector resistance reads 1.04 KOhms , whilst the right hand connector (which is central of the three connectors) reads Open Circuit.

This ties in with the fault report which depicts the resistance range should be between 600 Ohms & 1.8Kohms.

I'll jack the car up & check further & report back any findings.

 

[BDE1V]

Well nothing to see there... Slotted ring looks ok.
Thinking about it, if the sensor is magnetic then the ring won't have any effect at all.
I can only see the ring giving problems with ABS once the wheels are rotating.
This is a hard fault once the ignition turns on & since the cable seems to run from the sensor through to the plug It's a case of a u/s open circuit sensor.

 

[Stratman]

I've just read up on replacing the brake light switch on a W203, and the procedure is slightly different to what you have done.

Fully extend the plunger, this resets the switch.

Fully depress the brake pedal and while holding it in position, insert and lock the switch into position.

Slowly allow the pedal to return to its stop. This automatically adjusts the switch.

 

[yodamop]

thanx ,car is booked in for nxt wed.just seeking advice ,my slk has thrown up a Cpl of probs abs asr and vario roof in one day.tryin to prepare for the bill !!!