Red temperature light

[Danh]

Hi everyone ive got a 2006 honda jazz 1.4 i had a new temperature sensor fitted but now the red temperature light stays on 24 hours a day never goes out had sensor checked and car put on a computer with no fault found when car starts from cold blue light comes on then goes out after a couple of minutes but red light always on permanent any ideas why red light won't go out car does not overheat been to loads of garages and no fault found could it be the cluster as the mileage led also is now blank hope someone can help car also had new battery cheers Dan

[E27006]

Workaround:

Buy an ELM327 adaptor with bluetooth , (Ebay .. about £10) , download Torque Lite  Phone App (free),   select in  Torque lite app the  display gauge Coolant Temperature on you phone screen,  while driving  you can see  which components   of the ECU, sensor, cluster systems  are working correctly

[embee]

Was it the correct temp sensor? Why was the original one changed?

With a new problem, always look first at the last thing that was done.

[nowster]

Your punctuation has gone and there's nothing controlling the stream of consciousness. 

My suggestion is the same as embee: did the correct replacement get fitted?

[Ozzie]

I'm thinking the sensor wants to work with a gauge rather than just the two leds . . . . but I'm no auto electrician.

[culzean]

Pretty much every sensor will go to ECU module. Engine Temperature sensing  will be a thermistor - but if it is for overheating may be either a thermistor or a physical bi-metal contact ( this is not shown on Haynes wiring diagrams ).  Guess the signal for the red 'high temp' LED originates from ECU output - but cannot understand why LED is lit with ignition off,  unless it also runs the cooling fan for a while after ignition turned off ( some cars do run cooling fan, like my wifes Punto used to EVERY time you turned ignition off - and it wasn't even a 'hot' hatch ).

I would think if it is a 'proper' engine overheat warning the engine radiator cooling fans would be running while the red light is on. But it may be a failed ECU output that is keeping the LED on, in which case the fans may not be switched on.

https://www.dash-lights.com/honda/jazz-dashboard-warning-lights/

Your punctuation has gone and there's nothing controlling the stream of consciousness. 

OP didn't use punctuation because he doesn't want to come to a 'full stop', or for his tyres to deflate from a punctuation object.

[E27006]

Why was the sensor replaced in the first instance?
Do we know of a basic  test of the sensor?
Such as a measurement for  the resistance in ohms of the sensor while dipping the  business end of sensor in either hot or cold water.
The Honda workshop  manual  may have the specification for resistance vs temperature for assessing the  component

[E27006]

A thermistor is a  device having a negative coefficient of resistance (ohms) vs temperature (Celsuis).
When cold the thermistor is high resistance(ohms),  low resistance (ohms) when hot.
If you are showing a red light, the ECU is probably reading  a low resistance from the sensor circuit , please check the garage has installed the sensor correctly, I think the sensor is short circuited, a trapped wire or the connector damaged or mis-wired.
You mention the mpg gauge is blank,  a long shot, but do they share a common line or feed in the wiring diagram? If you disconnect the sensor, does the mpg display return to normal?

[nowster]

A thermistor is a  device having a negative coefficient of resistance (ohms) vs temperature (Celsuis).

Actually, positive temperature coefficient (PTC) thermistors exist also and are commonly used as self-regulating heating elements.

[culzean]

A thermistor is a  device having a negative coefficient of resistance (ohms) vs temperature (Celsuis).

Actually, positive temperature coefficient (PTC) thermistors exist also and are commonly used as self-regulating heating elements.

Yeah, they use them in those face sauna steamers,  egg boilers etc. etc.

[E27006]

I'm thinking the sensor wants to work with a gauge rather than just the two leds . . . . but I'm no auto electrician.

The ECU will read the coolant temperature sensor using an ADC channel in the ECU, (analogue to digital convertor) The ECU will calculate coolant temperature from the ADC value,  the computer code in the ECU will compare the reading with defined values and display the blue light , coolant cool,  red light , coolant temperature too high, no lights , coolant within normal operating range.
If the coolant is too high in temperature you would expect the ECU to command the radiator fan to run, but this is not happening with this fault,   a pity we are trying to solve this problem at a distance

[Danh]

The sensor was from honda main dealer the car runs fine blue light on when cold then goes out so they said the sensor is working but red light on all the time even when car is locked up over night computer says no fault codes found car doesn't over heat runs fine

[Danh]

The sensor was from honda main dealer the car runs fine blue light on when cold then goes out so they said the sensor is working but red light on all the time even when car is locked up over night computer says no fault codes found car doesn't over heat runs fine

I'm thinking the sensor wants to work with a gauge rather than just the two leds . . . . but I'm no auto electrician.

The ECU will read the coolant temperature sensor using an ADC channel in the ECU, (analogue to digital convertor) The ECU will calculate coolant temperature from the ADC value,  the computer code in the ECU will compare the reading with defined values and display the blue light , coolant cool,  red light , coolant temperature too high, no lights , coolant within normal operating range.
If the coolant is too high in temperature you would expect the ECU to command the radiator fan to run, but this is not happening with this fault,   a pity we are trying to solve this problem at a distance

[E27006]

Reviewing all the information  in the posts to date,  I've reached the conclusion, the red light is a fault on the instrument cluster.