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Discussion Starter #1
Hi all

Looking for yet more advice for my R129, 1998 SL320, if anyone would be so kind! Seems like it's one problem after another at the moment

Anyways, I went on holiday during the first two weeks of December, came back, started the car and the BAS ASR warning light appeared whenever i pushed down on the brake. Did some research and discovered this is a common problem, and it usually fixed by changing the brake light switch. So I ordered a new switch (admitidley a cheaper after market one) and installed last night...

...the new switch hasn't fixed the problem, the BAS ASR light still comes on when I press the brake pedal... I also noticed last night that my brake lights are on all the time, regardless of whether the brake pedal is pushed down or not.

I'm going to reinstall the old switch tonight to see if the brake lights are on with constantly, as I never checked this before installing the new switch

Has anyone got any advice at all, before I take it to my local garage and get charged ca$h mon€y

Thanks
Rex
 

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R129 500 SL 1991
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If you disconnected your battery the ABS/ BAS lights will illuminate after reconnecting. To reset, start the engine and turn the steering wheel all way to the right, then back to opposite lock, 3 or 4 times.
 

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Discussion Starter #3
If you disconnected your battery the ABS/ BAS lights will illuminate after reconnecting. To reset, start the engine and turn the steering wheel all way to the right, then back to opposite lock, 3 or 4 times.
Thanks robm... I'll try that tonight. How long should I leave the battery disconnected for?
 

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R129 500 SL 1991
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🤭 I didn’t mean for you to disconnect the battery.

The ABS/BAS dash lamp is known to illuminate IF the battery voltage is too low (<11v), or it went flat, or was disconnected and reconnected. Just try the steering wheel reset procedure first, without disconnecting battery.

If that doesn’t work read the codes with a scanner. It might either be the BAS switch, or an ABS wheel sensor.
 

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Discussion Starter #5
🤭 I didn’t mean for you to disconnect the battery.

The ABS/BAS dash lamp is known to illuminate IF the battery voltage is too low (<11v), or it went flat, or was disconnected and reconnected. Just try the steering wheel reset procedure first, without disconnecting battery.

If that doesn’t work read the codes with a scanner. It might either be the BAS switch, or an ABS wheel sensor.
Thanks I'll try the reset tonight. Is there anyway to tell when the reset has happened, or do I just keep turning the steering wheel until the light goes out?

Apologies for my ignorance, and thank you you for your help so far
 

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Discussion Starter #7 (Edited)
Hey.
Tried the reset, nothing’s happened.
Same problem.
So, I removed the new switch (which had the brake lights on ALL the time) and put back the old switch. Brake lights now only come on when I push the brake pedal down, BUT I still have the same original problem...
...the BAS ASR light is off until I press the brake and then it comes on.
Should I check I the fuses or the third brake light?
 

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R129 500 SL 1991
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Hmmm... :unsure: makes me wonder if you installed the new BAS switch correctly. Did you adjust it?

When installing new switch, pull the plunger all the way out, push brake pedal with your hand and install the switch. Release pedal and pull pedal upwards. You should hear the switch click a few times.

If this doesn’t work out then run a fault code scan to check for faulty BAS switch or BAS module.

Beware that some aftermarket BAS switches might not be compatible, although they may claim to be. Usually safer to purchase genuine MB.
 

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R129 500 SL 1991
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When you read the codes with a scanner, make sure the scanner is capable of reading ABS codes. Most simple code readers cannot read these codes. Take it to an MB dealer if in doubt.

I mentioned low battery voltage. Another possibility is a faulty steering angle sensor. The latter would render a steering lock to lock reset useless.
 

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Discussion Starter #10
Hmmm... :unsure: makes me wonder if you installed the new BAS switch correctly. Did you adjust it?

When installing new switch, pull the plunger all the way out, push brake pedal with your hand and install the switch. Release pedal and pull pedal upwards. You should hear the switch click a few times.

If this doesn’t work out then run a fault code scan to check for faulty BAS switch or BAS module.

Beware that some aftermarket BAS switches might not be compatible, although they may claim to be. Usually safer to purchase genuine MB.
When I installed the new switch, I didn't follow this process. I just removed the old one, unplugged the two sets on wires, plugged them into the new switch and then put it back. The plunger on the new switch was also shorter.

I'll purchase a genuine switch from theslshop and will install the way you mentioned.

If that doesn't work I guess it's going into the garage.

Thanks again for your help
 

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1998 Pano SL500; 1993 SL500; 2005 ML270cdi
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My '98 SL500 always shows the BAS/ ESP light when I disconnect the battery.
I always do the right left lock to lock a couple of times as well as the the windows up and down a couple of times.
I don't know if the window re-sync does anything but this always extinguishes the dash lights.
 
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