Ls400 Coolant Temprature Sensor Replacement

ambermarine · April 4, 2012

Hi Fellow Lexuns

I spoke in January on the replacement of the coolant temprature sensor on my 1990 LS400 ,that topic was about cold starts.

I have just returned from my annual trip to FLO where I purchased a new genuine Toyota(the part is a universal toyota part and fits in most of the lexus and toyota range of engines) part no 89422-20010 $52 sensor and a new set of the correct Denso plugs for around $54 thats half price of the UK for genuine Lexus parts.

I have since fitted the plugs and sensor and the difference in the engine responses are significant and very noticable.Firstly the idle speed which was running back in December at around 1200 RPM for up to 15 minutes before dropping to normal tickover of 600 RPM as now dropped to 4 minutes .The engine is a lot smoother probably because it is receiving the correct fuel mixture and the new spark plugs are producing the ultimate spark.

It is only when the changes in old equipment are made that the difference is noticed as the wear and tear on equipment is slow and hard to quantify.

The changing of these parts took a couple of hours as the covers for the spark plugs have to be removed to get at the engine temp sensor in addition the front coil and the spark plug leads and carrier have to be shunted to one side to get at the temp sensor.I did'nt drain the coolant because if you don't remove the expansion tank cap a vaccum is created and the temp sensor can be removed without a drop of coolant leaking .A deep 19mm socket is required for the sensor and it is only a torque of 15lb to remove and replace.

I did'nt disconnect the Battery and remove the dome fuse and when everything was reassembled and the engine started the engine warning light came on, when the codes were checked the engine coolant temp sensor showed as open curcuit confirming what I had done .After the dome fuse was removed and replaced normal code was resumed .If you do it this way you close out any anomolies that may have occured before you started the replacement of parts.

The engine sensor does not show a code fault if it is working the trouble is that in my case it was not working accurately as I found when I removed it and checked the resistance status at varying tempratures as per the workshop manual, it was way out and after 22 years that is not surprising.

I hope now to get better fuel economy better performance and the peace of mind you get with a Lexus when it is cared for.