Its at the shop right now and looking like that's their recommendation too.
Brake Booster Motor cycling on and off repeatedly
- Thread starter murphthelab
- Start date
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I hav had the exact same issue on my 2004 Land Cruiser. Just finished replacing the entire unit and it’s still clicking on and off. I’ll update if I figure it out.
Ever get this resolved? Same issue here now
Ever figure this out. I have the exact same issue. And I replaced the entire MBC assembly. With the same issue. Intermittent motor running to the cycle of the relay. I will say it does draw fluid from the reservoir. But it's not the constant motor running
Motor constantly cycling on and off is typically an issue with the accumulator, but best to replace the entire master cylinder assembly. If it is still constantly cycling after you’ve replaced the entire assembly you most likely have a leak somewhere in the brake system.
I'm currently fighting with this issue also. I replaced the accumulator and motor with a new set from City Racer, but not master cylinder. As soon as I turn the key on, it cycles for a few seconds at a time. It does suck down some fluid and build a tiny bit of pressure over time. I assuming the master cylinder needs replaced, but I can't understand why master cylinder failure wouldn't result in the pump running constantly until pressure is achieved, and then maybe cycling constantly as pressure is being bled off constantly. It really seems more like some electronic control is not allowing the the pump to run for more than a few seconds at a time. People have mentioned a pressure switch/sensor but I haven't seen a part number or description of this...
I had pretty much the same issue as the OP of this thread. Ultimately replacement of ABS ECU (89540-60150) was what resolved my issue. All across this forum people say that the abs pump running for a few seconds at a time repeatedly is accumulator failure. However what they fail to comprehend is that this issue is immediate from when the key is turned on. If accumulator failure was the culprit, the logical symptoms would be 1. pump running for 30+ second, then cycling constantly as pressure is bled off from failed accumulator. or 2. Pump running constantly until it either times out, or overheats (I assume there must be some kind of protection for not running the pump constantly indefinitely).
My point is that the pump running for only a few seconds at a time from the initial start is more indicative of an electrical control issue (brake pressure sensor on MC, ABS ECU, etc) than accumulator or MC failure. This is what I finally determined after an new oem MC/booster at $1400 didn't fix this issue. Unfortunately, I am not a good enough diagnostician to understand how you would go about properly diagnosing the ABS ecu failure. I can only suggest anyone in this situation borrow the part from a friend/club member, or buy a used one on eBay like I did. It would have been much cheaper and easier to try the ECU first, but I didn't trust my gut.
My point is that the pump running for only a few seconds at a time from the initial start is more indicative of an electrical control issue (brake pressure sensor on MC, ABS ECU, etc) than accumulator or MC failure. This is what I finally determined after an new oem MC/booster at $1400 didn't fix this issue. Unfortunately, I am not a good enough diagnostician to understand how you would go about properly diagnosing the ABS ecu failure. I can only suggest anyone in this situation borrow the part from a friend/club member, or buy a used one on eBay like I did. It would have been much cheaper and easier to try the ECU first, but I didn't trust my gut.