|How to test ABS Sensors with a Multimeter!|
Car: 1999 Rover 800 825 V6 Coupe
If the ABS light stays on your Rover 800, the most likely reason is that one of the four wheel sensors has stopped working! Although many other things can also bring on the light such as a split in a reluctor ring (located behind the wheels).
You can test for a faulty ABS wheel sensor using two ways. You can use a method similar to that used below, or if your car is fitted with an onboard ABS self diagnosis test you can use that, but you will need a list of the fault codes to understand the results. (see here; Rover 800 ABS brakes Self Diagnosis Test)
On this page though is the manual method of checking the wheel sensors. Most of the time a wheel sensor fault happens it is usually caused by a front wheel sensor rather than a rear one, and because the front ones are the easiest to check because they are much more accessible, this is usually the best place to start anyway.
All you need to do to check the sensor is locate the connections under the bonnet (or behind the boot carpet near to the suspension struts for the rear sensors), split the connector, then using a multimeter take a reading from each sensor.
Sensors that ARE working on this car should give a constant readout on the multimeter of approximately 1.5k to 1.7k ohms. If the vehicle is raised and/or the wheels are off the ground, turning the wheels (only if it is safe to do so) will give a reading that rises and falls, although the readings shown will still stay within the same range, but this will show that the sensor is working correctly.
Sensors that are NOT working will normally give a weird reading as the numbers on the multimeter will just keep rising.
Once you have found the sensor(s) that are no longer working, you can then obtain and fit replacements.
HANDY TIP: (When things get desperate!) If buying the replacement off a vehicle in a scrap yard, and the scrapped vehicle only has the sensor off the passenger side when you need the drivers one (or vice versa), you can still buy it, and by re-using your old brackets, fit it to the correct side on your car. (although this usually requires some difficult cutting and drilling to complete! I have had to performed this difficult trick several times on Rover 800's!)
1999 Rover 800 825 with ABS Warning Light On!
Locate the connector for the ABS Front Wheel Sensors under the bonnet, close to the suspension mounting. The Drivers side connector is seen here behind all the other wires/connectors.
Pull the connector out from its bracket and then using two small thin screwdrivers etc unclip the two sides of the connection.
With the connector unclipped, one side has two prongs, the other has two holes.
To take a reading put the multimeter in the side with the two holes, and take a resistance reading, it does not matter which wire from the multimeter goes into which hole. The difficulty is when the multimeter prongs cannot reach the holes and you get no reading, in this case you may have to compromise and use two panel pins, or two small nails, or needles in the holes and then take a reading off these. A working sensor will normally give a constant reading, this one was showing 1.56 ohms.
The connection for the ABS wheel sensor on the passenger side is again located near the suspension housing.
Unclip & seperate the sensor using two narrow screwdrivers or similar. Again one side of the connector contains two prongs, the other two holes.
Put the two wires from the multimeter into the two holes to take a reading. The reading on this sensor started low, then just kept climbing suggesting something was wrong this side.
The sensor reading continued to climb and so it was obvious this sensor was no longer of any use and was the one that required replacement.
After purchasing a replacement sensor from a local scrapyard this was tested prior to fitting. (Taking a multimeter with you to the scrapyard is always worthwhile to avoid purchasing a faulty sensor (or even having to remove a faulty one!). Some scrapyards say they can't be tested on a none working car, but they can). This one was reading 1.68ohms, they will always give there highest reading off a vehicle. If you want to, you can move the sensor back and forth near a metal object, such as your fridge or a spanner or something similar to see the reading rise and fall as it should when fitted to a car next to the metal teeth on the reluctor ring.
Need help replacing the Rover 800 ABS Wheel Sensor then click here!