Hi all, I've noticed a strange issue on my forever troublesome 2001 AP1. When I jab the brake pedal to get the car into ABS the front left wheel locks up while the rest of the wheels correctly engage ABS.
My ABS light bulb works correctly but is not on during normal operation. I imagine if the wheel speed sensor is an issue my ABS light would be one. I will try inspecting the sensor for issues as I've read in other somewhat related threads.

Here is a video of the issue:

 

Just checked the ABS sensor and it was spotless. The bolt holding it to the knuckle was not tight however. I tightened it and went for a drive and the front left wheel still locks up.

 

Are you sure that it's only the front left that's having an issue? If the ABS isn't engaging, perhaps that wheel is the first to lock and you're (understandably) releasing the brakes immediately to save getting a flatspot. Do you feel any pulsing from the brake pedal? If not, perhaps try the test again and really press the brakes hard to see if you can get other wheels to lock.

Other than that, I'd start with what's simple. If you haven't already done so, pull the caliper and make sure it slides smoothly and that the piston retracts. Might be worth bleeding the brakes to make sure you don't have air trapped anywhere. You know, look for anything out of the ordinary and make sure the rest of the brake system is in good order.

You've already looked for obvious damage on the wheel speed sensor and, besides, wouldn't it generate a code if it was not functioning properly?

If that's all good, seems like the ABS valve/pump could be the culprit.

 

Hi mate did u ever find out what was causing the wheel lockup as I'm having a very similar issue and tried all the usual stuff to resolve it with no result.

 

Nope. I plan to swap out the ABS modulator when I have some free time. I'll report back after I do.

 

You might want to try bleeding the brake line to the caliper that's locking up. If there is a little air in that line it's possible that it's acting like a pressure reservoir, not allowing it to pulse. Air can compress but liquid can't. It's worth a try.

 

I have been experiencing the same issues and have tried new tyres and pads all round, new front discs, refurbed the front calipers and ive done loads of brake bleeds including a full change to dot4, no difference. I did take it to honda and they couldn't find anything wrong. I'm experiencing most of the lock ups on the front drivers side so I recently changed the abs sensor on that wheel and still no change. Will prob try a abs module rebuild next.

 

You could swap the front sensors left to right as a diagnostic. The wire mounting brackets are different but you can zip tie them to road test.

 

I did think of that but considering changing the right abs sensor resulted in the old one getting obliterated, (I hear they all come out like that) I don't want to risk breaking the left one trying to remove it. I did checked both sensors resistance readings and they were both exactly same. I found a company that can rebuild my abs/vsa unit for £170. Will update if that fixes the problem.

 

Well I finally found the time to swap the ABS unit and I'm still having issues with the ABS. The behavior is a little bit different now though...

Depending on hard I get on the brake pedal the ABS will pulse but if I really slam on the brake pedal I get full lock and lots of tire smoke. Luckily I'm running on some old 7 year old tires so I don't care too much about flat spotting them. Given that the front left is no longer consistently locking up compared to the other wheels I'm guessing that the issue is related to air in the ABS unit.

Now that I think about it the ABS has never worked in this car and this car was rebuilt by the previous owner from a completely stripped frame... So it is possible that he was never able to successfully bleed air out of the ABS in the first place and by the time I had bled the system several times I had eliminated most of the air.

I was reading some older threads and Rob Rob had mentioned that it takes about 2 gallons of brake fluid to successfully bleed out all the air when replacing the ABS unit. Someone in that thread had also mentioned that if you had the OEM Honda scan tool you could manipulate the ABS unit and bleed it correctly.

I'll do some more bleeding and report back...