How do you test ABS sensors?

Hey all, I've been troubleshooting my ABS and traction control lights for a while now and would love a second opinion.

I added small suspension spacers to my 2011 Tacoma only on the front. We were careful to keep ABS line out of the way, but still after 4 weeks of driving, the ABS light and traction control light are both on.

I've tried the pin-shortage reset which didn't work. I was able to get the 2 lights to flash slowly, but after turning off, removing paper clip, and turning on, they didn't blink faster (aka they didn't reset I think). So, naturally, I resorted to testing continuity. Both ABS wires are fine and show the same voltage, but then I decided to test the ABS sensors.

ONLY ONE of the sensors showed any voltage, so I assumed it was somehow broken during the strut removal process. Not sure how, I was super careful, but anyway.

I wanted to get verification that the lack of continuity in the ABS sensor (I literally unplugged it from the ABS wire, and put my pins straight into the sensor plug) means it's broken. I already ordered and received an aftermarket sensor from Amazon to test out, but before I pull the original sensor, I wanted to get other thoughts on making sure it's actually toast.

Thanks in advance! Pretty newbie at this so any help is appreciated.

 

What's the code(s)?

 

I don't have a machine to read the code unfortunately

 

You need an oscilloscope to test the sensors. The signal is a 7-14ma current that’s monitored.They aren’t like the traditional inductive sensors that send ac voltages.

Your best step would be verify the trouble condition described by the code.

 

Just about every parts store chain will pull codes for free these days.

 

https://www.tacomaworld.com/threads/how-to-pull-abs-codes.205231/

 

We didn't test for voltage, we tested for resistance. We had "OL" which indicates there's zero current flowing from one pin to the other

 

I know, I’m telling you the procedure to test these is to monitor current(amerpage). You will always get an open or some crazy high megaohm. These are active sensors. They require voltage 12vdc to be turned on. I have not found the inner circuit diagram but I’m guessing transistor controlled.

They are back probed while installed and use of a scope to verify this wave form in mA. (Current) not voltage.

 

First thing is test is if you have voltage at the pins of the connector with the key on, if you don’t it’s likely a wire or connector issue. If you have voltage you can reconnect and monitor the feedback via OBDII reader. These are active sensors and require excitation for feedback.

 

I just got this to test the sensor on my wife's Prius. It's about $265 shipped form, new, fleabay (cpo outlets). Haven't tried it yet because it's been raining/snowing/really cold every weekend, but I LOVE wasting money on tools (so my wife says). My logic is: "look, the last time we had the shop diagnose (I didn't have the time, and it was the middle of Winter), it costs $280 for them to figure out it was the harness and replace it (other side ABS on the Prius a few years ago), so I spend this money now, and anytime there's a problem, it will make it easier!" But of course, now that I bought it, there will never be an ABS problem in my life ever, so my wife will still say "see, it was a waste of money."

So it's easier/faster than using a scope (I do have two - yes, I'm a tool hoarder), and the thing that makes it better than a scope is you can hook the harness to it and send a signal BACK to the module. Using a scan tool to watch the wheel speed PID, you can see if the signal is getting back to the control module.

https://www.hickokwaekon.com/automo...-pinpoint-tester-wheel-speed-diagnostics.aspx

 

This makes sense, thank you! So in your opinion, our diagnosis isn't enough to verify that we need to change the sensor?

 

Thank you! We're trying to see If we can borrow one from a buddie's shop. Any recommendations for testing the ABS cables themselves? We also just ran a standard continuity test

 

Testing with a meter is outlined in the FSM (checking resistance between pins from one side to the other). If you mean with the Waekon tester, that's the cool thing (that I haven't tried yet).

If, lets, say testing the sensor with it says the sensor is good, you can connect the harness to the tester, and try to send the signal back to the control module and see if it's getting there.

If you test the sensor from the end of the harness (instead of directly at the sensor), and it's bad, and you test the sensor directly and it's good, you know it's the harness. If you test the sensor from the harness end and it's good, then you test the signal back to the control module from the connector the harness plugs into and the signal isn't getting the the control module, you know there's either a problem between the harness and the control module, or the control module itself.

If you test the sensor from the connector at the control module, and it's good, you know it's the control module.

That's one of the cool things about this tester - it uses a 9v battery to send voltage to the sensor and read the signal back, so it's not necessary to have the sensor connected to the ABS circuit at all. I tried it on a bare hub (with built in sensor), and it worked great. This is compared to scope testing that usually requires the sensor to be in circuit with the module providing the voltage. That is especially problematic with cars that shut voltage down to the sensor if there's a problem.

There's a few vids on YouTube on using it. One is by Waekon (I recall), and one is by a distributor or manufactuer in Europe (where it's marketing by another company or perhaps related distributor). I think if you search "abs tester" or "waekon abs tester" it should come up.

 

Oh very cool, thanks for this! I don't think it extends past the harness, lights came on after a simple spacer insert in the top of my strutt. But yes I should double check like this

 

So the sensor was the problem. Took it out, drilled out the broken pieces, and replaced it with an Amazon one. We tested each sensor for continuity, the ohm-meter goes up to 2M scale, the front right read ~.900 aka ~900k-Ohms, the front left read OL. Polarity actually does matter in these sensors as the front-right gave us a value but when the polarity was switched we got OL. We verified that the new sensors work in that manner (they did and they showed ~900k-Ohms). The front-left sensor however read "OL" regardless of polarity. So if you have a meter that reads up to 2M-ohms or higher, this method can work before whipping out an oscilloscope. As far as I'm concerned with electronics - infinite resistance=open circuit=no point to test with an oscilloscope because no signal is going to reach the harness connector. Sensor was replaced and the ABS light disappeared. Sidenote - no fault codes were stored despite the ABS light being on. Does CEL need to be on for a code to be stored? Clearly the sensor had failed...

 

MOST times it's the sensor that I know of. I just used the possibility that it could be the harness and that the Waekon tester will make it easier as the excuse to the wife to buy it.

Not sure about the Taco protocol, but on the Prius, I cleared the code and the lights wouldn't go off (yes, the scan tool is ABS capable - Autel MS906). So it's likely the control module is seeing a short or infinite resistance at initial test. It's more likely to be the sensor in the bearing, especially where I think it's also making bad bearing noise (but I didn't tell my wife that lest the Waekon gets disapproved). Because I cleared the code, even though the lights remained on, there was no code when I rescanned until the sensor worked for a few seconds while driving then triggered again.

 

you need a meter capable of reading abs codes. Failure of a speed sensor does cause a MIL but a scanner not capable to access the skid control ECU will not be able to get the code.