ABS has a mind of its own...

2006, 2.7L, 4x4, 5 speed manual, access cab with 6ft bed. 219k miles

ABS light came on a few days ago here in Nebraska....just the ABS light. Not overly concerned as I imagined some water might have gotten down in a wheel speed sensor and frozen, figured I'd get to it when able....after a few days the light went off by itself last night.

This morning I go to drive to the store ....at low speeds (less than 20mph) both straight and in turns the abs pump would randomly kick on. This would happen when I wasn't even touching the brake.

Hit the brakes and the ABS would kick on. I promptly removed the 50 amp fuse for the ABS, then the light came on and I once again had normal breaks (minus ABS obviously).

Ideas and experience welcomed.

 

Most likely a failed speed sensor or broken a chunk/tooth off of the tone wheel the sensor reads from. Scan for codes to find out which wheel it is and go from there.

 

Any particular aftermarket brands to avoid or are wheel speed senors one of those absolute Toyota brand parts you need to use?

 

You need to find out whats wrong first. Ideally oem if its a harness or sensor though.

It 100% sounds like a sensor or tone ring, its sketchy in parking lots so be careful.

 

I went through a dick dance with wheel speed sensors a couple years ago - 1 DOA, 1 (different label) failed after a month, finally got hands on an OEM and no problems.

 

OK....Thankfully Toyota is still the truck of the warlords and ABS codes can still be pulled with nothing more than a paperclip. I reinstalled the ABS fuse, took the taco for a drive around town just in case the abs module would stop sending codes. Then I went home turned off the truck and jumped OBD II connecters 4 and 13. I then turned the key to the "on" position but did not start the engine. I then "pulled" the following codes by reading ABS blinks off the dash. The codes are as follows:

13: Open circuit in ABS control (motor) relay circuit
31: Right front wheel speed sensor signal malfunction
32: Left front wheel speed sensor signal malfunction
34: Left rear wheel speed sensor signal malfunction
41: Low battery positive voltage or abnormally high battery positive voltage

My thoughts:

Code 13 may have been caused by when I pulled the fuse earlier to keep the ABS from continuing to actuate when I was simply driving around on dry pavement (after all I could hear the ABS pump/motor going just fine several times this morning.

Code 31-34 I find it highly unlikely that all three wheel speed sensors would malfunction exactly within 48 hours of each other. I think these codes are symptoms of some other issue.

Code 41 I don't really have a clue. The only battery I could think to check was the actual vehicle battery itself which indicated a positive 13.75 volts with the engine running and a 12.6ish volts after the vehicle engine had been shut off. Perhaps some other battery exists inside the ABS module that I am unaware of that it is trying to indicate an issue on.

Edit: Brake fluid is clean, relatively fresh (less than 8 months old and less than 20K miles on it). About in the middle between the max and min lines.

What are your thoughts?:

 

13 and 41 are likely from removing the fuse, the others hard to say which sensor is the culprit.
You really need a scan tool that can display ABS data so you can see what the sensors are doing while driving and see if one is erratic or dropping out at low speeds.

 

Unfortunately I don't have a scan tool capable of observing that data. Mine is a very basic code reader. Any other ideas or ways known to check these things with a multi-meter or some other method?

 

No, you'd be guessing all day.

You could try reading voltage from each wheel but without references you'd be guessing in the dark.

 

What if I jacked up the rear wheels, left the vehicle in 2wd and used the right rear wheel sensor readings on a multi-meter as a basis with the wheels moving? That seems to be the one sensor that the system thinks is working properly right?

 

Not really, all you can do is see if the ABS module is sending the proper voltage to the sensor.
The only way to see what the sensors are doing is with a scan tool, the only way to effectively check the sensor signal is with an oscilloscope.

 

I didn't realize the sensors on my 06 where wide band.! Wow...they are getting fancy!

 

They are active sensors, all you would see with a meter is the bias voltage from the ABS module. The actual sensor signal is very small and would only be visible with a scope.
The old school VRS type sensors generated their own A/C voltage which technically could be seen on a meter but that would only tell you whether or not it is making a signal not that the signal is good.

 

Yea this allows the ABS module to determine the direction wheel is moving as well as being very accurate at low speeds.

 

If you know how to use a scope, you can get an inexpensive pocket scope. I have a Velleman HPS140 here that I occasionally use for nerd shit. It has been discontinued and I don't know what the replacement model is, but I know I paid less than $100 for it, I think more like $50.

I don't know if it will do what you need for ABS, as I don't know what kind of window they're outputting.

 

Active sensors are pretty difficult to read even on a decent scope due to them operating on minor changes in current rather than voltage, I have a Snapon Verus Edge and the voltage changes are very subtle. I just got a Pico but I haven't used it on ABS yet.
On vehicles with a hard fault I typically just use my test leads to connect one of the known good sensors to the circuit that has the fault and if the fault moves to the opposite side I know I have a bad sensor, if it doesn't I know I have a wiring or module issue.

 

So while this is a great discussion, I am concerned that even if I put a high functioning scan tool on this thing and drove it around that it would indicate I have three bad sensors (as it currently is indicating) and I truly don't think all three of them failed at the same time. That just seems extremely unlikely. Other than "wheel speed", what other information might one get with a higher functioning scan tool that would help me narrow down the issue?

 

You could always clear the codes and see what comes back.
I can tell you what I do with vehicles that come in for intermittent ABS complaints, I go on a test drive while graphing all the wheel speed sensors and look for any of them to glitch, drop out, or be inoperative and note when the problem occurs.
Examples:
If it's a front sensor and it drops out only when turning or going over bumps I'm gona be looking for a broken ABS wire on the front suspension.
If it's a consistent glitch in the signal I'm gona be looking for a damaged tone ring or failing sensor.
If the signal drops out at low speeds I'm gona be looking for an air gap issue or failing sensor.

Granted these are just some of the things I look for, certain vehicles I see alot of the same kind of failure on are pretty easy but some can be tricky to properly diagnose still.

 

Is the ABS module memory different from the ECM memory? To the point, if I use my basic scan tool to clear codes, or just disconnect the battery for a while, will the ABS codes be cleared so I can try this?

 

Yes it is a separate module, no a generic scan too will not clear it.
According to service info unhooking the battery will not clear it but you can clear it using the jumper wire method.