by M J Bradfrord
Date Added: Friday 31 May, 2013
It starts with the ABS light coming on intermittently at first, and then staying on. The usual cause of this is a broken wheel speed sensor, so the first job is to run some diagnostic tests to find out which one.
To check for DTC on the ABS system on MX-5 turn ignition switch to off, bridge the TBS and GND terminals in the DIAGNOSTIC socket under the bonnet, turn the ignition switch to on and count the groups of flashes on the ABS lamp.
I had one long and two short flashes. Front right wheel sensor failure. One long and one short flash would have been the front left. Tested with a multi-range meter at the connection points under the bonnet. Front left read 18000 ohms the right front nothing.
Ordered a Front Right sensor - got the usual fast next day delivery with a genuine Mazda part. Plugged it in and turned on the ignition and to my relief the ABS warning lamp went out.
Now it gets a bit tricky! After reading lots of horror stories on the net I decided not to mess about trying to undo seized components. Used an angle grinder with a thin cutting blade and sliced off the offending sensor and holding bolt. I removed the brake pads so the disc movement gave me a bit more room where the magnetic bit of the sensor pokes though the hub. Drilled out the captive bolt and went right through the hub so it would be easier to tap a new thread. Drilled a set of small holes all around the plastic part of the duff sensor. This made it loosen and it pulled out easily.
Cleaned out the sensor hole de-rusted it so the new sensor was an interference fit. Reassembled with copper grease. Don't do as I did drop the new sensor in the metal fillings produced as it has a strong magnet and it will pick up all the bits!!