Gearbox temp SENSOR
Handy Howie
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When you buy a second hand car, if you are like me, you always presume there is at least one fault on the car that the previous owner is hiding from you.  I believe it is rare that someone just wants to upgrade their car, but is instead prompted by a fault they don’t want to pay to get fixed.

Upon driving my 1999 Land Rover Discovery 2 TD5 on the first decent length journey, a little warning light lit up on the dashboard.  The user manual told me that this meant that the automatic gearbox oil was overheating.  This could mean one of two things, either the gearbox was at fault, which would no doubt be expensive to fix, or the sensor needed replacing.  Since there were no other symptoms, I decided to spend a few pounds on a new sensor and see what happened then.

The new gearbox temperature sensor fitted to the gearbox oil cooler ready to be re-installed

After taking off the panel above the radiator you can look down between the air conditioning condenser and the engine radiator and see the gearbox oil cooler.  This is fastened at one end by a hook and a screw at the other end.  You can see the small screw in these two photos.

The engine radiator can be left connected to the hoses and can be manoeuvred so that there is room to lift the oil cooler out.

Before I fitted the new sensor I performed a few tests on the two sensors.  I placed them both in hot water and measured their resistance. The sensors seem to be simple bi-metallic switches that turn on at a specific temperature.  The old sensor switched on at too low a temperature and also gave erratic readings on my ohm meter.  Since fitting the new sensor the gearbox warning lamp has not lit even on very long journeys.