Have you checked the VSS (Vehicle Speed Sensor) on the gearbox ?

P0500 relates to VSS 1 which is on the left hand side of the gearbox. If there's a fault with it or it's wiring it flags up the P0500 code as the wheel and rear diff sensors won't correlate and the speedo won't work.

In regards to checking the wheel sensors, you'll need to use an oscilloscope and see if the wave pattern matches the other known good ones as the wheel is rotated. Checking resistance will show you nothing except the resistance of the component. Sensors like these need a dynamic not static test.

Good luck.

Err.. not quite.

An infinite resistance shows a wire is broken.. a common sensor fault...

And no resistance shows an internal short..

So using a multimeter can identify two major causes of failure.

Edited by madf on 07/07/2014 at 09:33

{If you get the car up on axle stands and run it with a diagnostic tool, You'll be able to see the road speed from each wheel given by the sensors. It is the best way of testing them}

What diagnostic tool are you talking about here , are you in the UK and is it available here?

Cheers PAT

OK, many thanks guys , I didnt see the editd post by madf, I will have a look at his suggestion of multimeters.

I have since done another test with a more sophisticated meter and founfd that there is possibly a diode in the diff sensor and it measures resistance both ways one higher than the other, this of course the diode only lets current one way. So by switching the fluke to Ma and passing a metal object , (this is out of the housing by the way) it shows fluctuations so a good indication something is working , next step is to try this sensor back in the diff.Then I can test the rest.

Does anyone know where I should be looking to spot the other speed sensor please on the gearbox , I have a feeling that this where all my problems lie.

madf,

You are of course correct, but I don't think you understood where I'm coming from. The OP has already tested the resistance of the sensors and found them roughly the same so that would suggest they are electrically sound. However, testing this way won't show if the sensor is actually reading the reluctor ring for whatever reason : poor air gap, dirt/debris on the magnet, missing/broken reluctor etc.

The most reliable way to test if all four wheel sensors are giving a [correct] signal is on a reasonably good diag computer (I've used the Bosch KTS many times for this) but there are others available, and using the live data you can select the four wheels and see what the readings are.

Alternatively, if you have access to a good quality multimeter that has an oscilloscope function, you can attach the leads ( to the sensor wiring plug ) and get a wave pattern like the one shown in the PIC of this link : www.tme.eu/html/EN/digital-multimeters-with-oscill...l

Hopefully, this has cleared up the confusion ?

I spun each wheel quickly when I tested with a multimeter...

Edited by alfapat on 08/07/2014 at 00:48

I have had the front abs sensors giving a pulse on Mv but nothing off the rear sensor on the diff , although it measures the same resistance as the front two.

The sensors have two wires and seem to have a diode in them as the resistance shows higher one way to the other.ie 3.20ohms compared to 18.3 the other way , perhaps explains the plus and minus showing in the plug end.

I have looked at the gearbox and only found what looks like a reverse switch on the passenger side , nearside UK.Petrhaps this is the VSS sensor someone mentioned?

I think someone is thinking of a different model here, unless I am mistaken of course?

Edited by alfapat on 10/07/2014 at 14:28