BAS ESP Light.

[R-Connor]

I bought my W202 C180 with this fault already on. The light doesn't always come on. It's completely random.
After searching the internet for hours, i found it was quite a common fault. There are alot of people out there with ideas as to what may cause it but i haven't yet found an answer.
Is there anybody out there who can help me for sure?

 

[martyz]

Brake Light switch ok ?

 

[R-Connor]

Brake lights work ok so i assume so.

 

[martyz]

They may do,but this is a common fault that can be rectified by changing the switch
as it also sends a signal to the ecu.cheap easy fix search Brake Light Switch for lots of post's on this subject.

 

[andy27168]

Hi
Just because the brake lights work doesn't necassarily mean the switch is ok, and being as really your next move would be to get a STAR diagnostic carried out, I would replace it they are approx. a tenner from the stealers and easy to fit.
Regarding the esp fault it could be one of the body mounted sensors, a wheel sensor possibly the steering wheel clock spring etc. So getting a diagnostic is really the way forward the forum members generally reccomend brake light switch replacement first as it is cheap and can fix this issue.

 

[R-Connor]

New brake light switch ordered should be with me in 24 hours. Fingers crossed and thanks for tje advice.

 

[Dieselman]

The switch is virtually guaranteed to fix this fault, observe when it happens. It will be when first selecting drive or reverse with your foot on the brake to release the lever out of park.
The switch uses a flip flop and it's when it flips over without a clean contact it causes the problem

 

[R-Connor]

Ok. I recieved the new switch today. Can anyone tell me where on the car it is located.

 

[Howard]

Under the dash , behind the brake pedal , 1/4 turn to release.

 

[brianhogg1]

hi just read your post my bas esp light came on 2 ,i replaced switch to no avail,[ u have to disconect hand brake lever also, not hard tricky tho] traced fault to a brass knuckled sensor located on the brake servo [silver housing wae the ltter v on it .on further inspection i noticed wires under servo think one was bared due to heat chaffing? .i disturbed wire and wedged a rag between. light bin out til this day .hoping it stay out .

 

[R-Connor]

Ok. Changed the switch this morning. The problem has now got worse. The light comes on as soon as i start the car. I put the old switch back to eliminate the chances of the new switch being faulty.
To be honest. I haven't found one person that this has actually worked for yet.
Thanks Brian. That will be my next line of investigation.

 

[Howard]

Once you install the switch , you need to go from lock to lock twice with the steering wheel with the engine running to reset the fault.

Hard left to hard right to hard left to hard right.

You're kidding right ? 99% of the time the brake switch cures it. It has on all three of our cars. There are many other members who have sorted their problem this way too.

Good luck.

 

[R-Connor]

Silly me. Just refitted the new switch and did what you said. Took it for a road test and the light stayed off.
Thank you all very much for your advice. Lets hope it stays off.

 

[R-Connor]

Quick update. Took the car out. Got 3 miles down the road and the light came on.

 

[Howard]

Erm ....

Ok , how about the reluctor rings ? are they clean and free from dirt ?

They can trigger a BAS fault.

Failing that , get it on a STAR .

 

[andy27168]

At this point it would be best to get it on STAR as you can guess at what is wrong but without a proper diagnostic you will only be guessing.

 

[jefrs]

Mine kept doing this even I replaced the BLS (which was stuffed)

Mine would come on after several many miles typically on motorway.

I was dreading the reluctor rings, but no, they checked ok - a combination of various faults. Note we did check the reluctor wheel sensors

1) check the battery. What is easily enough volts to start and run may be not enough for the electronics. Mine was borderline so replaced battery - many regular random faults ceased.
2) thoroughly check the various earthing points. Brown wires bolted to bodywork hidden in engine bay and elsewhere. Electricity plus moisture equals corrosion equals oxidized ground tags and poor earth. Stopped PAS and ADS faults
3) check the various modules and relays in the black boxes are fully and firmly inserted so they make good connections. Particularly my ADS which did not want to click down under normal pressure. Stopped routine BAS/ESP fault except on motorway.
4) check (and fix) 4-wheel alignment. I had gradually replaced all the rubber bushes meanwhile, front and rear, drop links, top and bottom, track rod ends and ball joints too, the works.

All of this looks a pita, and it was, but none of it cost as much as I feared.
The last (4) was the expensive bit, in my case a cumulation of replace every single rubber bush, full alignment with a set of adjusted bolts added.
That's mine sorted,. Touch wood it has not recurred since.

 

[markjay]

On a previous car, a similar problem was resolved by replacing both the rear brake light bulbs, apparently the circuit that self-tests the ABS was affected by brake bulbs with slightly off resistance, not sure if this is also the case for the W202 though.

 

[horgantrevor]

Hi have you every or do you think the engine bay may have been power washed as their is a small black box in front of brake master cylinder three wires plugged into it it is for the bas control unit they take in water very easily and can cause a bas fault

I have changed many in the past with second hand ones from the scrap yard the code on them is the same for most if not all the w202 range

The star test will let you know

 

[jefrs]

The STAR test should tell you what is wrong. In my case it was telling fairy stories.

True the diagnostic codes were correct, but the cause of these faults was not.

That is, don't go replacing expensive bits when all you've got is a dodgy connector (you can fix those).

The hideously expensive bits are on the whole pretty reliable, the connectors pretty cheap, and look for moving parts to wear out, not stuff that doesn't.
If it ain't bust, don't fix it.