R129 ABS BAS Light - C1025-003 (Triggers 5 MPH<)

[DanMorgan]

Hey,

I have an R129 SL500 (1998) that's triggering the BAS/ESP Lights when reaching 5 MPH and they'll remain on.

Put the car on STAR and it's throwing a C1025-003 fault.

Is this a brake light switch fault or something else? I have another R129 SL500 as a "spares" car so plenty of stuff to try.

Cheers,
Dan

 

[Will]

If it’s triggering only when driving I would suspect something like a speed sensor, no idea on the fault code - have you googled it?

 

[DanMorgan]

That's what I initially thought but surely STAR would pick up the exact wheel sensor at fault?

I did all the searches and went down the rabbit hole of people guessing anything from the brake light switch to the wiring harness! Therefore created this - Hopefully, the 5MPH thing may be a common symptom.

 

[Doodle]

As Will suggested, not triggering until some movement screams a sensor - brake light switch would usually pop an error the moment you press to put it in gear.

Another less palatable option is that the ESP module is cooked, as from memory that's the remaining part of the chain

 

[Will]

Silly question but I assume it has the correct size wheels/tyres fitted all round?

 

[DanMorgan]

Planning on giving the sensors a clean at some point as that's what I thought - I just find it odd that STAR isn't highlighting that they are at fault.

I have 2 piece 18 inch AMG BBS with standard tyres etc (also ran these on my previous SL500 for many years too)

 

[91dm]

Is it intermittent or every time? I'd agree sounds more like a speed sensor not reading correctly.

Also check the wiring coming out of the abs unit and rear of sensors for any visible damage.

 

[colinallcars]

When our SLK lit up the same warning lights it was the yaw sensor at fault.

 

[Tonye]

Have you tried turning the steering lock to lock a couple of times to reset it. If that dont work you need to get it scanned.

 

[BTB 500]

Planning on giving the sensors a clean at some point as that's what I thought - I just find it odd that STAR isn't highlighting that they are at fault.

I have 2 piece 18 inch AMG BBS with standard tyres etc (also ran these on my previous SL500 for many years too)

Did your previous R129 have ESP? My '97 only has ASR (traction control), which I suspect wouldn't have an issue with different rolling radius front/rear. ESP would though, and of course nothing would show up on STAR. Just to confirm, the correct sizes are 245/40 R18 front and 275/35 R18 rear.

Otherwise was the car OK previously, and if so have you had anything done recently that involved the wheels coming off? ISTR that the sensors are quite delicate and can be damaged fairly easily by shock/impact.

 

[DSM10000]

The 5mph trigger is because ABS is deactivated below this speed.

Have you checked the voltage output on each wheel sensor? That should tell you if one is faulty.

 

[DanMorgan]

Thanks for all the comments!

To answer a few questions:

1) Happens without fail as soon as you hit 5 MPH
2) Tried the steering wheel trick but to no avail
3) I did change the wheels over but I didn't have any errors for a good month or so. I may check the tyre pressures to rule that out. Also, read up on a few of your ADS post - This car also has ADS too (rare for a SL500 I believe).
4) Ahh that would make sense - I will do this when the car is next on the lift - It has an AMG body kit current at paint, so will take all the wheels off then to give it a clean.

 

[BTB 500]

This car also has ADS too (rare for a SL500 I believe).

Yup. The SL600 had ADS as standard ... it was a fairly rare factory option on all other R129s (including the SL60 AMG), although typically seen on SL500s.

 

[alabbasi]

This could be the brake switch. You can also get this error from low voltage caused by a weak battery