ABS pump randomly comes on, no light - JeepForum.com
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post #1 of 11 Old 10-14-2021, 09:38 AM Thread Starter
rsmckain
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ABS pump randomly comes on, no light

1999 Jeep WJ Laredo, 6.0L, 4x4. I can feel the ABS pump randomly come on and off while driving. When it does this while braking I feel the brake pulsate. If the ABS motor is not doing this weirdness, the brakes are normal and smooth. There is no ABS light on. Codes show RF sensor, which I tested good but replaced anyways and the reluctor (spelling?) ring is clear and clean. I thought maybe I had a relay going out on me but it doesn't look like this year and model had a relay for ABS (I can't even find a decent wire schematic for this ABS). Any ideas?


1999 Grand Cherokee Laredo, 4x4, auto, 4.0L
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post #2 of 11 Old 10-14-2021, 10:31 AM
AVR2
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If the ABS light is off, then as far as the system is concerned everything is operating normally, so there should be no codes to pull.

So you're saying you can be driving along at highway speeds and the ABS pump activates? Or does it only do it at low speed? It does a dynamic test after startup, when you reach about 5mph, where it briefly cycles the motor but doesn't open the valves, so there's no actual braking effect.
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post #3 of 11 Old 10-14-2021, 10:50 AM
jtec
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What engine do you have 6.0L mentioned above?

Does the ABS light come on @ 2seconds every start then go out?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 11 Old 10-14-2021, 11:08 AM Thread Starter
rsmckain
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That's what I get for posting before I finish my coffee. 4.0L I6
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post #5 of 11 Old 10-14-2021, 11:12 AM Thread Starter
rsmckain
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I guess the ABS only comes on for certain codes or for a certain number of repeated codes?

So you're saying you can be driving along at highway speeds and the ABS pump activates? YES
Or does it only do it at low speed? BOTH (even at stop)

1999 Grand Cherokee Laredo, 4x4, auto, 4.0L
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post #6 of 11 Old 10-14-2021, 11:13 AM
Fzz
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Would warped brake discs/rotors cause a pulsating effect at the pedal?
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post #7 of 11 Old 10-14-2021, 11:17 AM Thread Starter
rsmckain
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normally yes, but the brake are normal as long as the ABS pump isn't doing it's random running bit

1999 Grand Cherokee Laredo, 4x4, auto, 4.0L
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post #8 of 11 Old 10-14-2021, 11:34 AM
Waterluvr
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We see this in the shop quite a bit on WJ's and mini vans of same era, when the pcb starts to fail on the pump there won't be any codes to pull or lights coming on.
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post #9 of 11 Old 10-15-2021, 05:42 AM
Delta0
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What's the answer please Waterluvr?
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post #10 of 11 Old 10-15-2021, 02:14 PM
AVR2
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Possibly the same fix as the common "motor circuit fault" code from the ABS - open up the module and repair any dry/cracked solder joints.
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post #11 of 11 Old 10-15-2021, 10:27 PM
Delta0
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Thanks AV.
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