When I first start my car and sometimes at random intervals driving it, my ABS control unit make a clicking noise, almost like a fan hitting something (but obviously not). I am 99% positive that it is coming from the ABS control unit as I can feel it vibrating when its making the noise. I can also feel the clicking/virbations in the brake pedal when I can hear the noise. Like I said, its very occasional and only lasts for 30 seconds at a time (or so). The brakes work well and none of the dummy lights are on in the instrument cluster. Any ideas what might be causing such a noise?

I searched on quite a few different terms and couldn't find much related to this problem.

Usually when an ABS pump kicks in you will feel the pulsing, this is the ABS Pump doing its work. I only notice mypulsing or ABS activation during hard braking or when I am on ice or snow. If it is doing it during normal braking you may have a malfunction in your braking system. A malfunction can be anything from a sticking caliper to unequal pressure, but it seems to me that you have a wheel that is potential to locking and the ABS is kicking in. Could be a speed sensor too. I would get the brakes checked to ensure everything is ok. Good luck!
Brian

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Brian W. Heitman

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I think that you're misunderstanding what i was trying to describe. My ABS is NOT being activated when the clicking noise is present (or ever under normal braking conditions). I know the pulsing feeling of the ABS and this is quite different. The ABS unit is making the noise and i can feel the noise just a little but in the brake pedal (it vibrates just a little). Like I said, it doesn't happen very often and only for about 30 seconds at a time maybe 2 or 3 times in a 20 minute trip (sometimes never).

in my 89 190e 2.6...

However, I may be facing an OVP relay issue which causes my ABS light to come on very occasionally...and causes my car to stall intermittently.

From time to time, and usually when I apply the brakes upon the first stop after pulling away, the brake slightly pulsates and I can hear a clicking noise. It may happen at other times during the drive as well.

My brakes are quite spongey so I'm chalking this up to a pad/rotor isssue, and not a malfunction of the ABS system...although you never know. I'm gonna pull the wheels and check the pads and front pad sensors to see if there is an issue there.

I'll let you know what I discover as it may shed some light on your situation as well...however, in the meantime, please reply here or email me at kevock@amnh, if you happen upon a solution to the problem.

Sorry, I cant be of more help as I'm piggy-backing on your problem.

Ok, so I am positive that it is coming from the ABS/ASR pump. It makes a clicking noise as if the pump needs to be oiled or lubed in some way. I'm not sure why its doing this or what effect his has on the ABS/ASR systems as they both seem to be functioning properly - i've tested them As I said earlier, neither the ABS or ASR dummy lights are on and the pump only seems to do it a few random times while driving (ie. I can not reproduce the noise by doing anything)

On a related issue, how (or does it at all) does the ABS pump interact with the ASR system. Looking at other e320's:


This e320 is without ASR and seems to have a "normal" sized ABS pump (common to many other w201/w124 cars)

My pump/unit on the other hand is enormous compared to that one (seen here for sale on ebay for 275):



and here on a wagon w/ASR:

no one has had a similar problem?? Am i just left to fork out the cash and replace the pump with a used unit?

I have not had a similar problem to what you are describing. The ABS interacts with the ASR by pulsing the brakes at a wheel that is shown to be slipping. Each wheel has a speed sensor, when the computer is notified that a wheel is turning faster than the others it sends a signal to the pump and the pump applies pulsing pressure to the brake on that wheel. I have had this happen with my SL and my S. I had the car up on a hoist and put it in gear. It doesn't sound like a clicking when it does it, it sounds like something rubbing and does not stop the wheel, just kind of kicks it a little bit. If you are not getting an ABS light, I would not think you have a malfunction in your ABS. Make sure they work, go down and empty road with no one behind you and slam on your brakes as hard as you can, if they pulse, grab and release (don't lock) your ABS system is working properly. If you are getting clicking while driving and not applying the brakes it could be something near or attached to your power booster/master cylinder. Check the vacuum line, make sure the booster is ok, you can apply pressure via a vaccum pump and see if it loses pressure, it could be pressure loss causing the clicking. If you have ABC, there is a switch in the power booster, It could be a lot of things causing the noise, if you feel it in your pedal how do you know it is the ABS pump, that is in the front of the car. I would not go and buy a new ABS pump if you have no warning lights and the system is functioning properly. If you don't know absolutely for sure what is wrong, take it somewhere and have it diagnosed. It is hard for someone to guess at what the problem could be without seeing it, feeling it, or driving it. Good luck!

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Brian W. Heitman

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I know that its coming from the ABS pump because when it is making the noise I have opened the hood and felt/pin-pointed the noise to the ABS pump at the front of the engine. Like you said though, the ABS and ASR lights are not on and both systems are functioning properly.

Does it do it while the engine is running? Do you have hydraulic fluid for the ASR? A separate resevoir? I had a 140 that would sit and click while idle, it was a consistent click perfectly timed coming from the pump while at idle. It turned out to be low on hyd fluid for the ASR differential. Just a thought maybe that could be your problem. I also noticed on mine the hydraulic lines that went down the drivers side of the car were hot, really hotter than usual, because when I heard the clicking I looked under the car and felt to see if I could feel the clicking. Check that out, maybe change the brake fluid and the ASR fluid. The ASR works through the pulsing of the brakes and pressure through the differential. Good luck!
Brian

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Brian W. Heitman

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Does the sound conincide with any feeling in the brake pedal?

If the device is clicking I would presume the solenoid valves are being activated. The pump isn't likely to click. It should whirr. I would first test your wheel speed sensors as they are notorious for unintended activations at slow speeds. I have never seen one activate while just sitting, but below the self test speed of 10kph it won't set a code or fault the system.

My guess is you have a power circuit to the actuator problem, or a speed sensor problem, or a controller problem. Unless the power supply problem is in the actuator I wouldn't suspect it.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

stevebfl: the feeling in the brake pedal is VERY different from the feeling when the ABS is activated. I am positive that it is not the solenoids being activated because it is happening at idle/stopped.

bwheitman: i am not sure where the hydraulic fluid reservior for the ASR system on the 94-95 w124 cars are but I would like to investigate this further as low fluid sounds like the source of the problem.

I'll post a pic of my ABS unit and engine bay so that someone can assist me in finding the location

I thought you suspected a fault. If so just what keeps the fault from being unintended application of the solenoids. Guess I just don't get it. The pump was mentioned, do you envision a fault that operated the pump to be more likely than a fault that set the solenoids into the sound you describe. I can't envision the pump making the noise you describe.

You described the situation and I described a senario. Just what does movement have to do with it.

ASR uses the same reservoir as ABS. There is a pressure reservoir that isn't in a ABS version.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

... and the pressure res has a bleeder on it that you may want to try checking for air in the res with...