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Can Bleeding the ABS cause a problem?

25 October 2001
Northern California
Curious, can anything go wrong in the process of just bleeding the ABS?

While my recent experience is with my 96 RL, I believe the question is also relevant to the NSX as well (though this has not happened to my NSX yet).

After the bleed done at the dealer about a week ago as part of 90K full service maintenance, the first few days after the bleed the ABS motor/pump kept activating itself under normal driving about every 5-10 minutes! It never used to do this. At one time the light came on and stayed on but once the engine was turned off and on again, it was back to normal. Yesterday morning after starting the car, the ABS motor kept going strong for about 15 seconds then it settled; hadn't done this before - and I know the difference from my NSX between regular activation vs. this particularly strong and lengthy one.

I have engaged the ABS several times and it seems to work though the light is not coming on when forced. I have an appointment with the dealer tomorrow. They think it is due to old age and are hinting that might be time to replace it! Would another attempt to bleed it help; could some vacuum gotten into the system? TIA.
The ABS pump continues to run anytime the acumulator can't maintain min pressure. If they let the resevoir run dry during bleeding (DOH!) and sucked some air into the acumulator, then bleeding it again may fix the problem. That is if they know to bleed the system at the acumulator, and not the wheels.

If the system is properly bled and still the pump runs too often, they need to test the acumulator capacity before condeming any part. The other possibility related to the previous service, though not their "fault" is that some debris from the system got into one of the valves in the modulator, and it is continuously leaking pressure internally. Another bleed may fix this, if it flushes the debris out of the valve seat.

I would talk to the Service Manager (as opposed to the adviser) when you drop the car back off and let him know that you are very concerned, having this type of problem immediately upon picking the car up from a major service. Hopefully, if he gets involved, you will get the best possible diagnosis.

Thanks Mark.

I just came back from the dealer before reading your post. They told me most likely there was a leak that the bleed accentuated. They said bleeding it again will not resolve it, no remedy but to wait and change it if it fails. So I drove the car back since leaving it there was not going to resolve anything.

Today, the pump did not activate itself untill I deliberately engaged it to test the system; the ABS is working. But no ABS light. Can the system have cured itself?!

I guess I can copy your post and fax it back to them for more input/response? From what i understand, they can't refill the gas.
Two updates.

Since my last post, at the next service which was in late December, they bled the ABS again and things worked out well just like normal. About two weeks ago, I had another regular service. The brakes were serviced with new pads and turned rotors as they needed them.

Today, I see ABS oil starting to drip very slowly on the floor right under the ABS. The ABS unit seems to be leaking. Where would this leak come from, the fittings? Is there anything else since this is a sealed unit? TIA.

Edit: Almost 12 hours later now, there is no longer a leak/wet spot under the car! I even had a short errand in the morning.
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A few things will cause the ABS to leak fluid on the ground.

1. A leak in the system. They are supposed to replace a soft hose on the ABS system during a major service. There are two banjo bolts and 4 crush washers that have to be torqued properly.

2. The constant pumping will cause the reserviour to overflow and dump fluid on the ground.

2a. As Mark pointed out: they may be caused by failure to maintain pressure

2b. The pressure switch may also be an improperly making contact. This is the sender/connector nearest to the drivers feet (LHD).

3. The bleeder screw is not happy---either not tightened properly, broken or there are debris on the sealing surface. Pack with rags and loosen/retighten to spec....it may cause a mess.

The Dealer is out of their mind if they think the ABS system has to be replaced.
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Between the brake service and your leak, did you here your ABS pump chirping away? Check to make sure there is no fluid at the top of the reservoir dripping off it. If a selonoid gets stuck, which I see alot, even intermittently, the fluid will bubble out the top.

This can happen, then the selonoid will unstick, and all works fine. Typically you may get a lot of ABS pump activity during these episodes.

Good observation Larry. Just a reminder, this is for my 96 3.5 RL.

The only chirping after the brake service and the time when I saw the leak, was the day of the leak (yesterday) when I started the car and it ran a solid 15 seconds with more grinding noise than usual. I knew it was the ABS so after I pulled the car from the garage stall, saw fresh, clean, light color oily fluid right under where the ABS would have been.

Yesterday, I tried to clean from the top and where the white plastic is with a rubber grommet/seal, also the connectors where I suspected. Will give it the degrease treatment to have a cleaner reference. Took it out again today for SMOG check, parked it and still dry.

Now for the more fundamental question, why would the solenoid get stuck? Wear and tear, dirt - even though this is the second bleed and 8 mos gave passed .....? Should I take it back for service?
The main cause is lack of use. The literally get stuck. This is why the typical recommendation to activate them regularly.