ABS Light On / Process to Correct / Fixed

Update-
Well, I’m feeling 0% inspiration and 100% desperation.
Got the brakes bled, and cleared the codes again. Got about two blocks down the road and the muther effin light came back on! I was so mad I could walk through hell with gasoline britches.
So, returned to the house and one abs code populated...CO210-right sensor.
Remember I replaced the left sensor.
So, the next step is I’m going to take the one I removed from the left side and put in the right side to see if there is any difference. If not, I’ll then take the new one (left) and swap to the right to see if the code changes.
Am I frustrated - Hell yes. But, no regrets on replacing the seals and one wheel bearing.
Gotta love it!!

 

The reason ABS brakes are the second thing to get disconnected after the clutch safety switch

 

You must get a meter on your harness (sensor to ABS module) and verify it's not the issue. You also should bench check your sensors to verify they're working. If all that's good it's the relationship of the sensor to the tone ring. It's one of those 3 things.

 

Wyoming09, I hear ya. If the ABS pump imploded then yeah I might would consider disconnecting but it’s GOT to be something in the rear.
I keep thinking about what Clint Eastwood would say....”a man’s got to know his limitations”.

 

Hey ShimStack. I know, but my knowledge of a multimeter is extremely limited. I’ve had a cheap Harbor Freight one for a couple of years but only used it a couple of times.
Last week I did use the multimeter on the rear sensor connections to see if they were getting power, but I’m not 100% sure I was doing it correctly nor did I trust what I was seeing. With the key turned to on (1 past acc), each one read 2.85.
This was with the multimeter turned to DCV 20.
Again, I’m not sure if that’s the correct way or not to check voltage.

 

The DCV is for measuring DC voltage and the 20 defines the scale or the max of the range. The DCV 20 will be fine for measuring DC voltage from 1V to 20V. I'm not familiar with the old wheel speed sensors but I see they are 2 wire so it could be active or passive. Looking at the pdf posted earlier in the thread and seeing the output signal is an AC voltage makes it look like you're working with a passive sensor. If it is, there is no power input to the sensor.

What you want to check is the resistances laid out in the test procedures of the pdf posted in the thread. Check the sensor itself across the two terminals and it should be 0.9-1.2 kΩ. Then check the resistance at each pin of the harness connector on the truck. Check this from each pin to body ground and it should be greater than 1MΩ.

This is the Ω setting on your multimeter and you'll use 2000 for checking across the pins at the sensor and then 2000k for checking each harness connector pin to body ground.

I also think it's a good idea to test continuity in the harness for all wheel speed sensor wires between the sensor connector and the ABS ECU connector. This will identify any issues with the harness itself, and while testing the resistance of each pin to body ground kind of does this it doesn't flag any unusual resistance in the harness or connections that may throw trouble codes at speed. Will have to search around for documentation to ID the pins in the ABS ECU connector as I haven't seen it in this thread. You can go one by one and just make sure you find one that has continuity and very low resistance.

Finally the ultimate test is to log the signals yourself with a data logger or watch it on an oscilloscope to see the sensor output when driving. I don't know if this is available on techstream for your model year (my 1st gen doesn't have ABS so I can't check), but it'd shed light on the issue immediately.

G'luck you'll get it.

 

Very detailed and a great source for me and others! Thank you for taking time to put the checklist together.

 

Interesting stuff! I’ve had an ABS light on for the last two years. Mine started after I took my truck to a shop to have them do a front end inspection before a 2k mile road trip to the middle of nowhere, AK. ABS light came on shortly after picking it up and never dealt with it.

I think my issue is in the front end. I rebuilt it last summer, wheel bearings included, and one speed sensor magnet was super caked in metal/dried grease. Cleaned it up and installed everything and still have the light. I need to make a jumper for the OBDII port to pull the code I guess.

 

07/21 CONCLUSION
Okay guys, FINALLY this little adventure is over. Took my truck to the Toyota Dealer to have them diagnose the problem.


@ShimStack pretty much nailed it in his post above.
The tech showed told me that all four sensors were receiving the proper voltage so that ruled out a wiring harness. The right rear abs sensor was not reading a signal from the abs ring. He said he it was not seated exactly as it should be, and the sensor was recalibrated.
The tech may have been trying to make me feel better, but he said he's seen this a lot when people replace suspension parts.
So, in hindsight....which as you know is 20/20...I didn't need the left sensor that i replaced.
Having no abs light on the drive home was nice!!

 

Makes sense, glad it's all resolved for ya.

 

Great tech and great suggestions and great ability to write this stuff! It's not as easy as one would think to write it and explain it in a way that most grasp and understand it.
Can tell you know what you're talking about with this stuff

 

I guess at least the bearings and seals got done, right? So tech was saying the sensor in rear simply wasn't seated properly? Wasn't the code you pulled specific to the sensor you replaced?
Either way, it's great to hear that dumb light is finally off.... And a taco in the shape yours is in DEFINITELY deserves to have that ABS light off

 

Yes, both seals were replaced, and the bearing/abs ring replaced on the passengers side.
Yeah the code was originally for the right (passenger) and left (driver side) sensor. The right side had a small amount of gear oil getting past the seal, and the bearing appeared to have play.
Yeah, he said the right sensor was not sitting flush therefore not getting a reading on the abs ring. I don't know man. It just presses in and then secured with a 10mm bolt. Not sure what was done when he said it was recalibrated.

And a taco in the shape yours is in DEFINITELY deserves to have that ABS light off............THANK YOU!

 

Yes, an old thread, but one I'd like to add two-cents too, and hopefully to help anyone who stumbles (Googles) their way here:

Bottom Line Up Front:
You can see the signal (waveform) from your ABS sensors; know if the sensor is or is not working, as a last resort:


The figure above shows two signals: The upper signal is from the right rear ABS sensor, the black and white wires or RR+ and RR-, and the bottom signal is the left rear, the red and green or RL+ and RL-. Both are nice sine waves, driving straight at 20 mph.

Caveat Emptor
OK, I used an oscilloscope and my 2000 4Runner has a plug under the left rear seat (i.e., access to easily measure the sensor's signal in side the car). I acknowledge that most will not have an oscilloscope or easy access.

Why did I post this?
I also had an ABS error code, #33 "Right rear wheel speed sensor signal malfunction". I bought a new OEM sensor (it was expensive even a few years ago), but the new sensor did not solve the issue. So I re-installed the old sensor (don't recall why) and kept driving the truck for a few year(s), then realized my rear bearings were bad. Bought the real tool to pull the bearings, the installation went well, and the funny sound/wobble from the back, went away. I reset the ABS light; cleared the code. However, the ABS light came back-on, and only a moment after driving. This and other threads explained how to measure the sensor's resistance, voltage, check for continuity in the harness, look for grease and other obstructions on the sensor (i.e., its magnet), visually inspect the tone ring. To all of you, Thank you so much. The guidance was most helpful. Anyway, my old sensor looked good (resistance, voltage, tone ring) Well, I grabbed the new sensor from the basement, but decided to try one-last test: I stumbled on a diagnostic check in the Service Manual. Specifically section DI-406 of the Anti-Lock Brake System:


The most important step is to disconnect the sensors from the ECU. Do NOT connect the 'scopes leads in-line. There's a strict caution here, just Google oscilloscope ground lead - BANG. Plus, the inductive nature of the sensor means, it'll generate it's own signal and you don't need a power-source, like an ECU, to test the sensor.

Below, the left image shows I have disconnected the ECU from the rear ABS sensors. Notice the red circles. Although hard to see, the leads from the oscilloscope are connected to an adapter that I made: The right image shows a plug from a donor (junkyard) car that have been soldered together. This gives me access to four test points, RR+, RR-, and RL+, RL- to connect the leads:


In my case, the oscilloscope showed no signal from my old sensor. Yay, I now knew it was bad! (Imagine the image above with only one sine wave.) So, I re-installed my new sensor. Success. You can see the plot with both signals above! The light has been off since.

Thought
I now know that my (old) sensor was bad, code 33. But, I also got code 33 with the new sensor. So, I wonder if my worn-out bearings contributed some degree of wobble, that created an odd signal, and then caused the ABS ECU to throw code 33 again. My ABS light only turned off after installing new rear bearings and installing a new sensor.

I hope my post helps someone in the future.