How to test a wheel speed sensor on the cheap?

[Nayov]

Long story short, I had codes read on my '05 Frontier a few months ago and it said one of the rear wheels had a bad speed sensor. The problem is that in the interim I suffered a debilitating injury so as a priority this issue completely evaporated and now I don't remember which rear wheel. I'm now back in the saddle as they say, and decided to deal with this. I suppose I could have the codes re-read if I have to, but what fun is that?

I tested for ac voltage and getting nothing from both sensors (Ohms are within range) by spinning the wheels. I find it hard to believe both are dead. My question is this the proper procedure? It's a 2 wire system.

These sensors are terribly expensive so I'd rather not just throw parts at it.

 

[vwmaniaman]

check for a broken wire in the harness. Had that recently on my Dodge 1500 Quad cab. my tool from Harbor Freight said either bad sensor or broken wire to rear driver side wheel. Pulled off the protective cover on the harness and it was obvious. Figured it got pinched at some point on a garage lift. Glad to hear you are feeling better.

 

[MrHorspwer]

Originally Posted By: Nayov

I tested for ac voltage and getting nothing from both sensors (Ohms are within range) by spinning the wheels. I find it hard to believe both are dead. My question is this the proper procedure? It's a 2 wire system.


Only passive wheels speed sensors will generate an AC voltage by spinning.

Active sensors either use a hall effect or variable reluctance-type sensor and generate a digital square wave. If you have access to a scope, it's really easy to see (you'll have to leave the circuit intact and back-probe the sensor because the sensor is powered by the ABS module). If you say your Nissan has a two-wire sensor that doesn't generate an AC voltage, it's probably a variable reluctance active sensor.

 

[eljefino]

Do you remember if the code read "no speed" or "erratic speed"? I've had cars where there are sub-options for "badness". "No speed" could be a bad wire or completely dead sensor while the erratic one could be a porcupine of steel shards grown on it.

My GM experience shows broken conductors inside good-looking insulation right near where it flexes a lot.

I wonder if you could unplug all three other sensors, and perhaps the VSS too, to see if you get to a higher speed before the (a) warning light trips. Keep changing the corner that's plugged in until the dead one's plugged in.

 

[red7404]

what was the setting on the vom. i use to check the old chrysler reluctor on AC. but had to be on the lowest setting. when spun by hand it didnt make a big signal.

 

[clinebarger]

As MrHorspwer eluded to.....These sensors most likely produce a D/C Square Wave signal, NOT a A/C Sine Wave.


I don't have much in the way of good diagnostic info for your Nissan, However.....

*2-wire D/C sensors will have Bias/Line voltage on one of the wires.
*The other wire is your Signal wire that will produce a "High to Low signal" as the wheel spins.


This is operational theory.....Nothing particular to your vehicle!!!

*Let's say the Line Voltage is 5.0 VDC.
*Signal Voltage with the sensor unplugged will be Zero VDC.
*Signal High Voltage will be 2.0 VDC.
*Signal Low voltage will be 0.69 VDC.

The signal voltage will switch High to Low as the wheel spins, The switch "Rate" will speed up & slow down with wheel speed.....The voltage changes CAN be read with a DVOM a LOW wheel speeds (Turned by hand).
*Without a Graphing DVOM or a Scope.....You will not see a signature pattern which is detrimental to proper diagnosis of this circuit.

 

[Nayov]

Update: Took it to the dealership and $167 later they tell me that my guess that both sensors were dead is correct. To fix the issue, would cost $2,800. Even the service advisor couldn't keep a straight face and said to have it done at an indy for far less. I'd already done the front calipers and hoses plus lines. Everything else is rotten they say (no [censored], they are correct, I'd already torn it apart).

Specific to the issue, they want $1200 ($400 for each sensor, about) to replace 2 rear sensors. I just ordered 2 $15 sensors on line. Might be a waste of $30 but worth the gamble. Need to squeak this thing through a state inspection.

 

[Tundragod]

15 bucks each? No brainer...........

 

[Smokescreen]

$2800 vs $30

dang dealership...you scary!