# ABS wheel speed sensor resistance testing



## atikovi (Dec 27, 2011)

Getting a code for ABS malfunction referring to the left front wheel. Disconnected the sensor to check the resistance and got nothing, as in infinite resistance. Assuming the sensor is bad since they should have some resistance but checking here to make sure before getting a replacement.


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## NickD (Dec 10, 2011)

Nothing in the shop manual as usual, just a coil of wire wrapped around a cylindrical bar magnet, over the years, any where from a few ohms up to over 1 Kohm. So definitely should show continuity.

I like to use stick pins and get as close to the sensor itself just because it could be in the connector or in one of the two wires. If that is the problem, will even hard wire these in, its not a like an electrical hand drill you want to constantly plug and unplug. And if it does go bad, can always cut the wires and solder and new in. 

Wonder if these are using those stupid insulation displacement connectors, piercing the wire of bare copper with a bare brass pin. Haven't had problems with mine yet, but sure will sooner or later with all this road salt. 

Can always get a reading from a "good" sensor


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## atikovi (Dec 27, 2011)

Not getting any reading from the two pins in the connector. I'll get a sensor from my parts car but at under $20 from the dealer, almost not worth the trouble.


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## ChevyGuy (Dec 13, 2014)

If you have a parts car, I'd check the resistance on that. Maybe it's a coil - maybe not. It could be a hall-effect sensor.


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## NickD (Dec 10, 2011)

Cruze is using the coil, only two pins, Hall Effects require a 3 pin connector. Nice you just have to buy the sensor for the Cruze, on other GM vehicles, had to replace the entire wheel hub that only cost $$$$$$$.


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## ChevyGuy (Dec 13, 2014)

NickD said:


> Hall Effects require a 3 pin connector.


I googled. It looks like some Halls are 2. Like this one. (The package has 3 leads, but one is not connected.)

I'm not sure where OP is measuring it. I'd think the wire to the wheel is more likely to fail.


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## NickD (Dec 10, 2011)

Is possible, had to switch on my brain, Hall Effect is essentially a bipolar transistor that is switched on by a magnetic field rather than a base bias current. But requires a series resistor to drop that voltage. If mounted in the sensor, three wires are required, ground, voltage, (5V typical), and the junction between the Hall Effect and series resistor for the signal output. 

But if that series resistor were mounted in the module to 5 volts, and where it exits the module with a tap on it for the signal, only two wires would be needed for the actual sensor. 

To me, ABS is next to worthless and another very expensive item to repair. If driving on glare ice, both left and right wheels will lock up, no differential in pulses, no ABS. If one wheel is on a higher friction surface than the other, then its activated, but what good do they do if that other wheel is on glare ice? Does pulsing it help you stop quicker, some Standford professor seems to think so, was given a grant to come up with statistics to prove they are 14% safer, so then congress made it law.

And because of insurance regulations, have to keep them in perfect operation or may not be covered in the event of an accident. 

Can't even visualize, the hydraulics can keep up with that high pulse rate, road salt rust the edges of the brake pads so they stick and won't respond. Other problems is that brake fluid gums up restricting the movement of those solenoids. That leads to another problem, driven by transistors that can short out with an inductive road, for that particular wheel, won't get any braking at all!

Cruze took another step by using the rear brake solenoids to save a couple of bucks on proportioning valves. If the ABS doesn't work, can get full braking on the rear wheels resulting in a skid. 

Another addition to ABS is traction control, if one wheel spins faster than the other, pulses the brake on that wheel to help prevent a skid. One thing for darn sure, an 89 cent microcontroller will never replace a limited slip differential to prevent that slippage.

And another, ABS will never replace the stopping power of studded snow tires. Just feel the world is going nuts. And that 89 cent microcontroller is way way overpriced! Just another legal means to screw the consumer. Should be warrantied for the life of the vehicle since they made it a federal laws. Can say the same thing about airbags.


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## atikovi (Dec 27, 2011)

That did the trick. ABS light is off, so are Stabilitrak and steering lights.


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## ChevyGuy (Dec 13, 2014)

atikovi said:


> That did the trick.


What did? New sensor?


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## atikovi (Dec 27, 2011)

Used sensor actually.


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## NickD (Dec 10, 2011)

Opened some of these up, using something like 55 AWG wire embedded in epoxy, thermal variations expand and contract only takes one tiny coil to break open. If they just coated that coil in silastic first as a buffer, wouldn't have been a problem.

Good coils are layer wound with insulation between each wire, the vacuum impregnated with varnish and should last forever. These are random wound, talk about super cheap. DC and AC also makes a difference, with DC a shorted turn just lowers the resistance an insignificant amount, still works. But with AC like these ABS sensors are, one shorted turn can kill the signal. Same with an ignition coil. Here a resistance check is worthless, do have special equipment to determine a shorted turn. But won't find this in the average shop.

If this problem occurred once, will happen again and again. Sure made ABS law, but no laws on the longevity on the crap they are using. And crap it is.


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## Robby (Mar 1, 2013)

This is a rather common failure as the miles pile up.
The sensor itself is well sealed and generally never fails, but the wires from the plug to sensor often break under the insulation.
Infinite resistance (open circuit) results.....the abs is sending current to the sensor and nothing is coming back, so, a code (light) is set.

Since the sensor wires rise and fall with suspension travel, over time, the wires within the insulation work harden (like bending a coat hanger back and forth, it finally breaks at the bend point) and fracture in two.
It starts as a intermittent abs light, sometimes only when wet or cold......the wires (multi strand) have but maybe one or two strands still making contact.
As suspension movement continues, those finally break apart and the abs light becomes a steady on concern.......replacement of the sensor and sub harness is the needed repair.

Operation in areas with rough (poor) roads will obviously hasten this failure as well as around town usage where front wheel left/right travel is frequent will experience this type of failure at lower mileages.

Rob


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