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-   -   ABS Pump Engages Until You Hard Cycle the Brakes (https://www.jkowners.com/forum/stock-jk-tech-dept/377361-abs-pump-engages-until-you-hard-cycle-brakes.html)

GunnersJK 05-15-2018 04:22 PM

ABS Pump Engages Until You Hard Cycle the Brakes
2008 JKU Rubi. I've had the Teraflex Big Brake Kit on the front for 5 years now, no issues. I only mention as it is my only brake related mod.

I've had a series of issues I've pecked away at over the past few weeks with the help of a mechanic (not dealer), and I am down to one. When you first start the vehicle after letting it sit for a bit, then drive away and touch the brakes, the ABS pump kicks in. The left front wheel wants to lock up, meaning it locks and releases. I live on a dirt road so I can look out the window and watch. Even a feather touch to the brake causes the pump to engage. Press a little harder and you feel the brake that is locking release. Hit it it hard a few times and it returns to normal for the duration of your drive. Let it sit for 15 minutes and it starts all over.

Here's a little more for reference. Right now there are no ABS dash lights. Previously I was throwing multiple codes, one indicating a right front (not left) intermittent failure of the ABS sensor, and all the expected dash lights were on. We replaced the sensor. Issue remained, and, all the related dash lights continued to light up. I also had codes for the cam and crankshaft sensors. Replaced the crankshaft sensor and no change. Replaced the cam sensor (had to order) and an issue with the engine went away but the ABS light issue remained, which you would expect. The mechanic cleared the camshaft codes this morning so I am now code free and no check engine light (which was not brake related), but I still had the ABS issue, dash lights in full glory after a short drive.

The mechanic thinks it is the hub (six months old) as there was a lot of metal dust on the tip of the sensor when he replaced it. So we swapped out hubs with an old one I had that was good and still had the same issues. But, I drove it about 45 miles, multiple stops, then on the way home the dash lights went out, no codes showing on my head unit, and it was working perfect. I parked it, ran an errand three hours later and the ABS pump issue returned. But, this time, even after slamming the brakes to make the ABS pump issue clear, no dash lights. I did not notice this time if it was pulling in one direction.

Also, I talked to Teraflex about the brake locking up. They can't explain it, but to rule out the caliper, at their suggestion, I pulled the caliper, disassembled it and cleaned it on the bench. Pistons are fine, proper movement, nothing wrong with the left front caliper.

And, that's where I am. When you first start out the ABS pump kicks in. After a few cycles the issue goes away. No lights (at the moment) on the dash. The mechanic is getting me a new hub for the right front, which I don't think I need but he is getting it for free so why not. We install that in the morning.

If this doesn't fix the ABS issue, any ideas?

rlee 05-15-2018 05:18 PM

The sensors work off a tone wheel. Sometimes the wheel can get corroded or damaged and give a incorrect wheel speed without throwing a code. Get a scanner that can read wheel speed and see which one is reading differently than the other 3.

GunnersJK 05-16-2018 12:13 PM


Good point, and we've done that already. While driving the speeds shown for all but the right front are consistent. The right front reads an intermittency. Say you are travelling at 30mph. For a moment or two it shows 30, but then drops down to 2, or 5, or 12, or some other number.

We replaced the hub and sensor this morning just in case, no change. Leaning toward a wire short or maybe the ABS controller being bad.

I still don't understand why the left front brake locks up when you first start. That happens as a result of the ABS pump firing. After several times braking the ABS shuts down and the dash lights come on, and the LF brake is fine. Makes me suspect the controller.

Any other ideas? Tks.

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