PicoScope 7 Automotive
Available for Windows, Mac, and Linux, the next evolution of our diagnostic scope software is now available.
2 Wire Active Wheel Speed Sensors
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Mark Dalton
- TwoWaves
- Posts: 106
- Joined: Mon Dec 01, 2014 9:35 pm
- Location: Melbourne
2 Wire Active Wheel Speed Sensors
I was carrying out some testing on a car the other day for a RHR wheel speed sensor open/short DTC. From the circuit description given by the manufacturer I took the sensors fitted to the car to be a 2 wire active sensors.
Part of the diagnostic guide asked me to check for battery voltage at one terminal, which didn't sit well with me, many of this kind of sensor I've tested the ABS module has disabled the circuit as soon as the DTC is set and stays disabled till the DTC can be cleared safely. So in looking for some data to confirm my though, I came across another piece of information found in the Pico Guided tests for Hall effect and MRE sensors which said "active wheel speed sensors must never be subjected to resistance tests: this can damage these units, with the only remedy being the acquisition of a new replacement.". But in the diagnostic guide one of the tests literally ask you check the resistance of the sensor.
Has the manufacturer got it wrong here? Particularly since on this particular vehicle the wheel speed sensor is part of the Hub/Bearing assembly and is in the hundreds to replace.
Are any of these kinds of sensors safe to carry out resistance tests on?
Are any of these kinds of sensors safe to carry out resistance tests on?
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Steve Smith
- Pico Staff Member
- Posts: 1594
- Joined: Sun Aug 25, 2013 7:22 am
Re: 2 Wire Active Wheel Speed Sensors
Hello Mark and thank you for the post (I feel another great discussion coming on)
Based on the principle of MRE operation and the switching of low current (normally 5 to 15 mA) the thought of carrying out a resistance check with a meter capable of exceeding these operational values suggest damage may be caused.
To be absolutely honest, I have never tested these sensors in such a fashion and not sure what to expect resistance wise!
Based on the By-Pass testing carried out here viewtopic.php?p=88281#p88281 the MRE sensor resistance under test would appear to between 750 and 1000 ohms
The “In-vehicle” volt drop method of MRE resistance testing (using the ABS ECU as the supply) would appear to be the safest route to obtaining a resistance value within the circuit based on current flow
The value in your 2nd image suggests 467.9 kΩ, I am assuming this is across the sensor? (I maybe misinterpreting Step 3 in the image)
I hope this helps, take care……..Steve
Based on the principle of MRE operation and the switching of low current (normally 5 to 15 mA) the thought of carrying out a resistance check with a meter capable of exceeding these operational values suggest damage may be caused.
To be absolutely honest, I have never tested these sensors in such a fashion and not sure what to expect resistance wise!
Based on the By-Pass testing carried out here viewtopic.php?p=88281#p88281 the MRE sensor resistance under test would appear to between 750 and 1000 ohms
The “In-vehicle” volt drop method of MRE resistance testing (using the ABS ECU as the supply) would appear to be the safest route to obtaining a resistance value within the circuit based on current flow
The value in your 2nd image suggests 467.9 kΩ, I am assuming this is across the sensor? (I maybe misinterpreting Step 3 in the image)
I hope this helps, take care……..Steve