I had an overheating issue a couple weeks ago on my 2003 HSE. The reservoir cap broke under pressure from the cooling system. We found the water pump was bad and replaced it, and checked the for gasket leaks to make sure there were no other issues allowing air into the system.

When we started the vehicle back up, the water temperature gauge would not register any heat and the red light came on.

We replaced the sensor and still have the issue.
The system has been completely bled, there is no overheating of the vehicle, yet we are not able to register a temp on the gauge and the light remains on.

Is there a place to reset on the ECU?

Any suggestions of what to do next?

 

If the temp sensor was bad - the check engine light would be on.
I would get a code scanner and look for a pending code.

I would get a code scanner and attach it in live scan mode and read the temperature
from the code scanner.

IF there is NO reading on the code scanner then your temp sensor is BAD.

I would also assure the system is FULL of 50/50 mix.

The radiator cap blowing off of the tank IS A BAD sign.

If you unclip your coolant tank and get it up in a position much higher than the rest of the engine - then fill it.

Then run the engine for 5 minutes or so - coolant SHOULD NOT come flying out of the top
IF it does - you may have head gasket problems and combustion gasses entering the
cooling system and the pressure ruins the weakest links - the cap and the hoses.

 

No codes. The engine has ran for several days, no leaks no air getting back into the system since water pump was replaced. No gasket leaks, no air issues.

Sensor has been replaced.

All the temps check out, running 194.

It will not read any pressure nor will the red light go off.

 

Try to reset the codes with the scanner.
Even if there are none.
Maybe that will reset the ECU.
Guessing on this.

 

Red light may be a different sensor.
That sensor may be shorted.
Just replace that other sensor which is actually a switch that goes on when the engine gets really hot.

You could also try to disconnect the positive cable from the battery and it it drain for an hour.
Turn the key on for a few seconds with the battery disconnected to drain any remaining voltage in capacitors.

Then reattach the positive lead to the battery (WITH THE HOOD SWITCH WEDGED DOWN).

See how that goes.

Personally, I think it is hard short.
But, I don't have a Discovery II electrical .pdf book to help you.
Sorry.

 

hmmmm.... from the RAVE, workshop manual, under "instruments" on page 1494 of 1529 - you find this:

If the engine coolant temperature gauge receives no input or the input is out of range the
temperature gauge will read cold and the high coolant temperature warning lamp will be illuminated.


So broken wire will do it, or bad connection. If your data reading scanner reports logical changes in the coolant temp, then problem could be between dash cluster and ECU.

 

I guess it would pay off to read the RAVE since I have downloaded it. I do believe it is a loose wire or a short somewhere. It started working last night and the temps on the scanner are 194 at idle, 200 while driving.

Thanks for everyone's help and input.