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[Johnny English]

Hi all, I had an issue with my crank sensor, which gave incorrect signal and at the garage insisted of swapping it off. I asked them to check at first visually and I was right as just a little deposit disturbed into the proper work. I want to aviod this awkward situation to be occurred in the future so do anybody here have any info about measuring sensors whether they are right or not? I mean checking of resistance, capacity or any property to conclude something in connection with theirs status. I need info about Lambda, Crank, Cam, Maf, Temp sensors either advice, experience or link would come handy.    Thanks guys,    Laszlo

[freecall666]

you can test a good one and a damaged one and it will be the same its the metal pin in side that is the problem over time they heat up and move so the sensor cannot read, on acashion the diode inside can go but not very oftern.

[cem_devecioglu]

Hi Laszlo,
 
although I'm not  competent in electronics, I also have "some" experience on car sensors..
 
general approach in car industry is dont touch until you have the code stored for the related sensor.. but sometimes this approach will be too late and you will be left in the middle of nowhere..   because most ECUs are designed to raise error when the sensor is completely dead
 
most of those sensors are sensitive devices and in time (and by heat) and with use they loose some of their accuracy.. and you can find that by directly comparing with a healthy one which I did (expensive method)
 
of course you can buy an expensive tech 2 and check those sensors directly or some kind of cheapo tester and use for the same purpose..
 
measuring their impedance, voltage etc is another method but in that case you have to know exactly how a healthy one behaves.. and besides  there may be many factors effecting your sensors accuracy , like your cars cabling condition, chasis, alternator and battery and also some other factors which is hard to guess .. but you have to go between pins and cables and take measurement from there which is sometimes messy..
 
so its upto you to what approach you will choose..
 
here are some test links from youtube
 
http://www.youtube.com/watch?v=6ws8EVQ6NjE
 
http://www.youtube.com/watch?v=IzZNlPosGSY
 
http://www.youtube.com/watch?v=SLgdaWCuKVo
 
http://www.youtube.com/watch?v=NdGPuerxuvU
 
 
 ps: I must note that, those sensors are not designed for cars life time.. for example lambda sensors avg lifetime is said to be 100K kms under normal conditions.. crank and cam sensors hard to tell .. knock sensors rarely go.. maf , definitely unpredictable lifetime..
throttle position: I changed and it improved.. so my opinion is sensors must be also accepted as wear and tear items..

[Johnny English]

Thx guys,  my basic skill is electrician technician so measuring or buggering among wires is not standing too far from me. Must admit though I'm not familiar with sensors. These links seem quite good !      Laszlo

[Andy H]

Some sensors are easy to test (for example the coolant temperature sensor) because they give a simple resistance output.

Other sensors are extremely difficult to test because they give a pulse output in response to something happening in the engine and you need to know how they work in order to connect to them without damaging them. A brief list:
Cam position sensor - hall effect sensor needs a power supply from the car to drive electronics inside it, gives a strong pulse for every revolution of camshaft).
Knock sensor - piezo electric crystal bolted to side of block gives short powerful pulses if pre-ignition occurs.
Crank position sensor - coil of wire in plastic housing gives several very weak pulses for every crank rotation (probably 36-1). The usual mode of failure on an Omega is that the insulation on the wire gets brittle due to heat and the signal gets lost. Not worth testing for, just buy a new genuine sensor (& route the new wire away from exhaust manifold).

Generally the easiest way to test the sensors on a modern engine is to hook the ECU up to a code reader that gives 'live' readings and see what comes up on the screen. The only one I would be confident I could test with a multimeter would be the temperature sensor.