MRE sensor (Nissan Pathfinder 2007)
Nissan Pathfinder 2007 MRE sensor – break in a plait of ABS
It’s no secret that the most common wheel speed sensors are inductive. They have a relatively simple design and are fairly easy to test. But all inductive sensors have a weak point, they cannot generate voltage at a slow speed of rotation of the wheel or shaft. And car manufacturers, in search of an alternative, chose a sensor that meets all the requirements and, unlike inductive, is able to record the minimum speed of rotation and movement of an object or assembly.
This sensor is the MRE sensor (hereinafter: MRE or MPE). The operation of this sensor is based on a physical effect referred to as “Magnetoresistance” or “Magnetoresistive Effect” – read description discovered back in 1856. British physicist William Thomson. The basis of this effect is the change in the electrical resistance of the material under the influence of a magnetic field.
Unlike Hall sensors, MPE sensors are oriented not by the strength of the magnetic field, but by its direction, as a result of which the accuracy of the sensor does not deteriorate as the magnet ages or the properties of the magnet change under the influence of high temperatures (which the Hall sensor cannot actually boast of). In the automotive industry, MPE sensors are used in ABS and in many other systems such as:
1) navigation systems (in electronic compasses, etc.),
2) measuring the speed of rotation (for example, automatic transmission, etc.)
3) Control of angular coordinates (this is the seat and steering adjustment system)
4) And non-contact current sensors with galvanic isolation (this is a power supply system with load control).
The MPE sensors themselves, which are installed on cars (Fig. 01), directly combine the magnetoresistive element and a signal processor (Fig. 02) that converts the change in the magnetic field into a current output of 7 to 15 milliamps (Fig. 03) .
Magnetoresistive sensors themselves cannot produce a signal voltage alone as inductive, and therefore must have an external power source, usually 12 volts. The sensor is powered and the signal is removed from it using a two-wire circuit.
I think that we have figured out the scope and internal circuitry of MPE sensors, it’s time to give real examples.
The hostess of this car turned to our auto service with a complaint about a malfunction of the ABS and all systems associated with it (antibuks, antizanos, etc.). Scanner indicates a problem in the rear right sensor circuit.
So, the repair manual for this car (Fig. 05) suggests in this case to use a dealer special device (Fig. 06) to check sensors of this type.
The note to this device says :
“… Active-type wheel speed sensors that mounted on this vehicle cannot be checked with a standard ohmmeter because the sensor is powered by the ABS control unit and the output signal is digital rather than analog (such as inductive).
Well, of course, I don’t have such a device (I’m not a Nisan dealer), but as they say, I had a trump card in my sleeve! Even before this case, I made a device emulating the signal of the MPE sensor to check the ABS system of the Mitsubishi Outlander XL (at the end of the article).
Having opened the circuit (Fig. 07) so as not to make a mistake with the polarity (I warn you, the sensors have a polarity do not mix up!) And connecting the emulator, I made sure that the scanner also does not see the signal from the rear right wheel, and the signal from the left rear goes without problems.
Thus, a malfunction can be assumed: it is necessary to search either in the harness or in the connectors from the ABS unit to the sensor since it is very rare that the sensor is covered and the wire is interrupted (litter for a pun)
Further, everything is simple: a diagram, checking the wire harness for an open circuit and searching for an open circuit using FF310 (Fig. 08), here it is the place of a clipping (Fig. 09). Happy end!
Many will probably ask: “And if the harness were intact and there was no emulator”? In such cases, I connect an ammeter to the open circuit of the sensor and take a reading by turning the wheel. A similar procedure for checking the MPE of ABS sensors is indicated in the Mitsubishi manual, for example, about Mitsubishi Outlander XL.
It shows the scheme of checking the MPE sensor without the use of special devices using only an ammeter and battery (Fig. 10), I just want to warn again about the polarity of the MPE sensors if the connection error the sensor burns!
For information, the structural diagram of the sensor (Fig. 11)
Therefore, see the manuals, for example, MOTORDATU! (Fig. 12) where indicated (+) and (-) lead to the sensor.
If you do not have a circuit, make preliminary measurements of the supply voltage and current from a working symmetric sensor.
And the circuit of the emulator itself is:
Kudryavtsev Mikhail Evgenievich
Nick on the forum “Legion-Avtodata” AVTEL
MOSCOW Auto service “VTS”
Suzdal St. 9
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