ABS pump runs WHEN KEY IS TURNED ON and brakes are OFF

406 Views 22 Replies 6 Participants Last post by scottseidler, 4 d ago

scottseidler

Discussion Starter · 19 d ago

Hello all!
I havent had to post in this forum in so long I think I had to start a new account! However the other day our 98 SLK230 threw both the ABS and ASR light on the dash and there was a loud humming from the engine bay. That humming was coming from the ABS pump which was just running on and on. Pushing the brakes stopped it until you released the brakes again.
I have not wanted to drive it to get the codes read as the pump continually was running so I have been searching for a way to power off the pump. Today i found the "power" connecter on the pump housing and yanked it stopping the unit from running when the key was on. I still have the ABS and ASR lights and for sure the ABS is not working at the moment!
I plan on running it over the the local auto parts place to get the codes pulled over the weekend and see what that tells me - but all of the research I have done online has not shown me this particular issue. I see pumps running continually WITHOUT the key even on - I see lights on - no pump whirring - etc.

Has anyone seen this particular issue before?
Thanks
Scott

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1 - 20 of 23 Posts

LeonardoDaBenz

· #2 · 19 d ago

@scottseidler * bump *

Reactions: 3

BaD_81

· #3 · 19 d ago

Sound strange!

The ABS pump is controlled by the ASR computer (running by memory here) based on what the ABS/TCU/Gear selector are feeding.
In other words, ABS sensor being out sends a signal to ASR (lack of rpms/open circuit/etc.) the ASR calculates the input data and spits a command - close the holding solenoid on RR wheel (open/close is electrical, but the pressure is coming with the pump working and that involves the brake booster). Executing the command you have a certain feedback - pressure based I think (a bit questionable, however if no ABS sensor input = no speed being changed, no feedback...) and that unit with sufficient fluid level, no air in the system should stop!

So, if something was done on the brake lines recently, have you bled them?
Running over something that ripped a sensor cable?
But my best approach (SDS scan is the best approach) with no scan printout is checking each wheel ABS sensor for disconnected wire. Is there power supply or TCU. These for the ABS/ASR light, the rest is...a bit too difficult!

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scottseidler

Discussion Starter · #4 · 19 d ago

BaD_81 said:
Sound strange!

The ABS pump is controlled by the ASR computer (running by memory here) based on what the ABS/TCU/Gear selector are feeding.
In other words, ABS sensor being out sends a signal to ASR (lack of rpms/open circuit/etc.) the ASR calculates the input data and spits a command - close the holding solenoid on RR wheel (open/close is electrical, but the pressure is coming with the pump working and that involves the brake booster). Executing the command you have a certain feedback - pressure based I think (a bit questionable, however if no ABS sensor input = no speed being changed, no feedback...) and that unit with sufficient fluid level, no air in the system should stop!

So, if something was done on the brake lines recently, have you bled them?
Running over something that ripped a sensor cable?
But my best approach (SDS scan is the best approach) with no scan printout is checking each wheel ABS sensor for disconnected wire. Is there power supply or TCU. These for the ABS/ASR light, the rest is...a bit too difficult!

Thanks for the reply @BaD_81
The car was last moved around in my driveway about 2 weeks ago. This issue was not present at the time. Prior to that it had been out once or twice in the past few months - again no issue with the ABS pump or lights. The problem started when my daughter got in the car yesterday morning started it up and tried to pull out of the garage and heard the loud pump noise and saw lights on the dash. She shut the car down and left it in front of the garage - so it traveled maybe 20 feet.

Last work that was done was probably 6 months back and had been primarily to the Transmission (faults). I THINK they did brakes as well and I just sent an ask to my daughter to verify. It has not been driven much since then at all - but have not seen this issue. She DID have an issue with the coolant light popping on for no reason - but that only happened once or twice.

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Avel Du

· #5 · 19 d ago

Any fluids where it was sitting?

Reactions: 1

BaD_81

· #6 · 19 d ago

Not being driven much, did you have a battery maintainer attached? Because low charge is pushing the electronics in the car beyond their comfort zone...sort-a-speech

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Avel Du

· #7 · 19 d ago

BaD_81 said:
Not being driven much, did you have a battery maintainer attached? Because low charge is pushing the electronics in the car beyond their comfort zone...sort-a-speech

And a low battery throws all kinds of errors. Always a good starter for 10.

Reactions: 1

scottseidler

Discussion Starter · #8 · 19 d ago

Avel Du said:
Any fluids where it was sitting?

None.. no leaks

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scottseidler

Discussion Starter · #9 · 19 d ago

Avel Du said:
Any fluids where it was sitting?

None, no leaks

scottseidler

Discussion Starter · #10 · 19 d ago

BaD_81 said:
Not being driven much, did you have a battery maintainer attached? Because low charge is pushing the electronics in the car beyond their comfort zone...sort-a-speech

I did not and that battery has gone low enough to need a charge at least once in thr last few months.
I dont know that it shines any light however on thr pump running when the key is on thought. Dash lights sure i can get that.

Reactions: 2

BaD_81

· #11 · 19 d ago

Start with good overnight charge or few days on trickle charge. After that connect those cables of the ABS pump and see if the issue is still there! Not bad idea to have the battery health checked, like properly loaded and a printout, so you see what you can expect.

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scottseidler

Discussion Starter · #12 · 19 d ago

Can do!

Reactions: 1

slk230red

· #13 · 19 d ago

5

I had a similar problem with my ABS pump. I drove 2 miles to a CVS store, turned the engine off and locked the doors. I heard a noise coming from the engine compartment. The ABS pump was constantly running. I drove back home and removed the ABS Pump power cable from the fuse block. I had my indie friend perform a complete scan, it pointed to a defective ABS Control Module. I purchased a used pump/module out of a wrecked '01 230 from a salvage yard and replaced just the module. Problem solved.

It was a tight fit to remove and replace the module, but it's doable. I think the '98 has a different configuration.
Good luck Scott.

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scottseidler

Discussion Starter · #14 · 19 d ago

Thanks Slk230red! I saw your thread actually. Only difference is that mine only run with the key turned on foot off the brakes. It wasn't running the whole time. Id hate to buy a replacement abs unit and have the same issue. So im trying to narrow it down. I am planning on getting a.scan done this weekend which might help.

Reactions: 2

BaD_81

· #15 · 19 d ago

'98 has the pipes in so insanely designed way, it make you wanna rip them pipes off

Reactions: 1

Dave2302

· #16 · 19 d ago

It will almost certainly be the ABS Pump / Controller Unit as @slk230red says. Not a very very common issue but it does happen, hence I have done a few. Just fit a new one.

Reactions: 4

scottseidler

Discussion Starter · #17 · 19 d ago

So battery charged overnight - 12.8vdc this morning. But pump still runs and lights still on. Off to get the codes read this afternoon, but I am thinking it is likely a pump issue. For now I have pulled the power plug out of the unit to shut it off.

Reactions: 2

Dave2302

· #18 · 18 d ago

scottseidler said:
Off to get the codes read this afternoon, but I am thinking it is likely a pump issue. For now I have pulled the power plug out of the unit to shut it off.

The Module will not communicate if un plugged, so be sure to tell the guy with SDS that it is unplugged.

If he's not using SDS then you might just as well swap the unit anyways, and I'm not a gambler, but I would bet that it is the ABS / ESP Pump and Module unit

Reactions: 2

slk230red

· #19 · 18 d ago

Dave2302 said:
The Module will not communicate if un plugged, so be sure to tell the guy with SDS that it is unplugged.

If he's not using SDS then you might just as well swap the unit anyways, and I'm not a gambler, but I would bet that it is the ABS / ESP Pump and Module unit

Just for the record, my indie friend had me connect power to the ABS pump when he performed the scan.

Reactions: 3

scottseidler

Discussion Starter · #20 · 18 d ago

Hey guys - just read these last posts. Yes I connected the power cable back to the pump but sadly it was a no go. I am assuming the inova unit that autozone uses cant seem to scan the SLK. They tried it running and just with the key on and got zero codes - and sadly showed a green check mark for the ABS. So it was a waste of time.
I am leaning towards going to ebay and ordering a used unit and just swap the assembly.

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