Hall Sensors

VW POLO

Volkswagen has always had an upstanding reputation (other than for the emission scandal) for manufacturing quality vehicles at affordable prices. One such car is the VW Polo hatchback which has also become one of the most popular cars in South Africa, and it’s really not hard to see why. The VW Polo is a compact car, but when driving it, it somehow feels larger, somewhat like its bigger brother - VW Golf. Should you buy one, you would certainly agree that the VW Polo has universal design appeal, that it has good performance, decent fuel economy and is sold at a relatively affordable price. 

Hall Sensor Hall Effect Sensor Switches A3144 / 3144E / OH3144E
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Volkswagen has capitalize on this winning formula for years and has given us plethora of Polo's to choose from ranging from the Polo Trendline, to the Polo Comfortline, to the Polo Highline, not forgetting the Polo Cross and Polo GTI which comes in 3 and 5 doors classic and hatchback versions. Engine capacities and engine technologies range from 1.2 TSI 66kW and 1.4 TDI 55 kW for the Trendline,   1.4 TDI 77 kW, 1.2 TSI 81kW for the Highline  and 1.2 TSI 81kW Highline DSG, to  1.0 TSI 70 kW BlueMotion. The sedan or VW Polo Classic comes in  1.4 & 1.6 trendline, 1.6 comfortline / tiptronic, 1.9 tdi highline (74kw)  and 2.0 highline (85kW).  There is even a GTI (Grand Touring Injection), a FSI (Fuel Stratified Injection), TSI (Turbo Stratified Injection) and a TDI (Turbocharged Direct Injection), to choose from. 

Clearly there's a Polo out there waiting for you! Having said that, owning a Volkswagen doesn't come without challenges, personally I think the biggest challenge is more likely than not the dreaded EPC light that triggers at the most inopportune times. The EPC circuit has several sensors that feeds into the ECU among them Hall sensors. From my experience hall sensors tend not to like heat, even though their specification sheets rates them above the requisite heat range.  

This datasheet gives you a good idea of a hall sensor's specifications 

Hall sensors are pervasive throughout modern day cars. Hall sensor, aka Magnetic sensors essentially converts magnetic pulses into electrical input signals for processing by electronic circuits. Magnetic sensors are solid state devices meaning there are no mechanical moving parts inside, its all electronics taking place in a sealed chip of silicon, making them immune to vibration, dust and water. This makes them popular choice by electronics designer engineers for several types of application ranging from  distance sensing, to velocity sensing, to position sensing, to  speed sensing, to directional movement sensing etc.

Hall sensors are used for angular position sensing of the crankshaft to determine the firing angle of the spark plugs. They are used for magnetic position sensing in EGR systems. They are used for wheel speed detection for the anti-lock braking system - (ABS) and speedometer. Throttle bodies with DC motors use hall sensors for position sensing. Hall sensors are also used to determine the position of the car seats and locking of seat belts. Hall sensors are employed in automatic transmissions as magnetic neutral position switch, as actuator sensors, as speed and direction sensors, for gear detection and clutch position sensing. Hall sensors are used as engine speed sensor and also as the vehicle speed sensors.  And the list goes on.

The following images depicts a hall sensor replacement inside the distributor of and Audi 5-cylinder engines 2.0 - 2.3. As can be seen the the wires have distinct colours , the red wire is +5V / 12V supply, the black wire is negative / ground and the yellow wire is the output of the hall sensor / sender.

There is space under the black plastic holder where the wires connect to the hall sensor.

Multi purpose hall sensor for automotive use, but the military spec hall sensor is a better option

The sensor is replaced, solder joints covered with fiber glass sleeving then epoxied into place.

Hall sensor plate reassembled

Hall sensor assembly fitted into distributor housing

As I mentioned in a previous blog, Hall sensors don't like heat and tend to malfunction when they get too hot. My first experience with hall sensors were when I was working as an electronics engineer for A Television and Video repair company. A video machines that employed a hall sensor in its take up clutch stopped working due to overheating.  By squirting the hall sensor with a blast of servisol rapid cooling spray, it started working again. I repeated this exercise a few times to make certain that the hall sensor was the culprit, after replacing it, the machine worked just fine. 

Then I also had a problem with my Opel Kadett 1.8 GSI  when driving in peak hour traffic. It would switched off and refused to start.  But after allowing the engine to cool, it started just fine and would be perfectly ok for days until I got stuck in bumper to bumper peak hour traffic again. The dealer had a field day with my car, telling me that they repaired a bad earth under the dash board, only to find out in peak hour traffic that they misdiagnosed. Then I was told that the loom was replaced, then I was told the ECU was replaced and finally that a hall sensor inside the distributor was replaced. This fix the problem once and for all. The images above is for the same symptoms on a Audi  2.0L 5 cylinder.  As perfect as hall sensors are for most applications, where there is excessive heat, they will misbehave.  Perhaps hall sensors mounted in heat intensive spots like the engine speed sensor, should be designed with a heatsink or have its own cooling fan. This advice is as relevant for current model cars as it was for the Audi 2.0L 5 cylinder.