ABS Kicks in at low speed while braking

[09fx4guy]

Good Morning everybody!

So, here is where I am at. I have a 2009 Ranger (FX4). Truck has 38000 miles, in good shape. The ABS system recently started kicking in when braking and turning at low speeds, like say pulling into a parking spot at a store. It has continued and now will engage when coming to a stop when straight. It only kicks in at speeds less that 3-5 miles and hour. There is no ABS light or brake light.

I suspect wheel speed sensors, and checked them. FSM says resistance should be between 380 and 480 ohms. Both sensors check out with 430-435 ohms. I will check the rear sensor a little later today. (Edit: Checked, falls right where it should at 1900 ohms)

My gut it telling me that I will probably need new wheel bearings, since there could be dirt or debris in there that really wouldn't be able to be cleaned out. I would probably use either Timken or Moog, since they seem to be the best available. (I'm open to recommendations).

If anyone has any guidance, it would be greatly appreciated.

 

[Dirtman]

Did you check the rear abs sensor as well as the fronts? They can also test fine but have a problem with the tone ring (broken teeth etc). Or the wire/connection can be damaged especially since you have a small lift and it happens when turning.

 

[Bgunner]

First off use a scanner that deals with ABS and has a graph. From what is described you have one wheel wheel sensor, possibly more but for sure one, that is the signal is dropping out at low speeds. This is usually caused by the magnet in the sensor becoming weak.

Use the graph section of the scanner and take the truck for a ride and make it happen. The graph should show which sensor is dropping out while the others are still reading wheels that are still spinning. Because one or more sensors are reading no movement while others are, the ABS system kicks in while your foot is on the break. EDIT: Brake... Gosh I always goof that one up.

 

[fastpakr]

I dealt with this for a while with my Forester. It was an ABS sensor that was dropping out at low speeds, indicating to the computer that the wheel speed had dropped to zero.

 

[09fx4guy]

That is pretty much what I had figured, a sensor going bad. I don't have a scanner that can show data like that, I just have a basic OTC.

 

[Bgunner]

Have you tried to pull any trouble codes the may possibly still be there? I know your light is off but curiosity has got me now.

 

[Uncle Gump]

Lets say when this happens... does the truck pull to one side or the other? If it pulls right... LF speed sensor is bad. If it pulls left... RF speed sensor is bad. If it doesn't pull... look to the rear.

 

[09fx4guy]

Bgunner- I tried pulling the codes with my OTC scanner. It does do abs and SRS, and it showed no codes. Sadly the scanner won't show live data so i can't monitor the sensors.

Uncle- It does pull to the right, and I kinda figured the left sensor could be the problem then.

I have a local mechanic who should have a scanner capable of looking at each sensor while i am driving / braking. This should then confirm my suspicions.


Just curious, does anybody have any opinions on wheel bearings, Timken or Moog? In the even I do have to replace them for some reason.

 

[09fx4guy]

Replaced the sensors last weekend (and upgraded to #1 torsion bars). The driver side sensor actually came apart when trying to remove it. The black plastic was stuck in the hole , managed to get it out with a pair of needlenose pliers. So far so good, new sensors were the ticket.

 

[Dirtman]

For the future, you can buy a scan tool with full PIDs that will give you wheel sensor data for a little over 100 bucks these days. The launch cr123 does it and is $120 and continues to drop in price since newer models are coming out. You can probably find one on sale for less than a hundred if you look hard enough.

Makes diagnosing issues like that take about 5 minutes.