coolant temp dashboard light

[beanbayli55]

Hi, just after a little advice please.

 

my wifes mk1 2000 yaris is having an issue with the coolant temp dashboard light.   I understand it goes off when at temp and red when overheating and blue when you start to say its cold.

 

the issue is the light either stays blue and on all the time, or it will keep going off and on again throughout any journey, meaning the engine is cold right?  Well using obd reader, the temperature is absolutly fine, sits at approx 90-95c , fan kicks in at around 93.  all radiator hoses have no leaks and both top and boottom hose get hot.  

 

i replaced the thermostat and coolant temp sensor but it made no difference.    Im looking for suggestions please on what else would cause the light to remain on most of the time.

 

thankyou.

[Derek.w]

To Beanbayil55  Coolant temperature sensor

Blue when cold below  60c

No lights on 61c to 116c

Red when hot above 117c

Clean electrical contacts on plug. 

Have you confused it with the fan switch? and changed wrong sensor.

Some have 2 or 3 fan speeds so watch fan as it heats up for it stopping instead of increasing its speed.

Is radiator thermostat air vent at the top.

[beanbayli55]

Thanks for the reply.  im 100% sure i changed the correct sensor, i will give the contacts a clean and see what happens.

[flash22]

IIRC there are 2 temperature senders one for the ecu and the other is for the warning light

what engine ? 1.0, 1.3 or 1.5

What sensor did you change, the one on the side of the head ? (you have to remove the air box to get to it)

 

1.0 or 1.3 temp detect sensor - right rear of the head (as you look at the engine) it on an elbow at about 45º

2 types

Denso - 89428-10120

or

Aisin - 89428-52010

Both cross to the same aftermarket parts

 

1.5 - bottom corner of the rad - 89428-20110

[beanbayli55]

10 hours ago, flash22 said:

IIRC there are 2 temperature senders one for the ecu and the other is for the warning light

what engine ? 1.0, 1.3 or 1.5

What sensor did you change, the one on the side of the head ? (you have to remove the air box to get to it)

 

1.0 or 1.3 temp detect sensor - right rear of the head (as you look at the engine) it on an elbow at about 45º

2 types

Denso - 89428-10120

or

Aisin - 89428-52010

Both cross to the same aftermarket parts

 

1.5 - bottom corner of the rad - 89428-20110

thanks for this, i will check the old haynes manual again for it.    Its the 1.0 engine, and the sensor i changed was the one right next to the thermostat on the side

[beanbayli55]

so them part numbers you provided point to the radiator fan temperature switch is that correct?

[Derek.w]

Your sensor 

I expect its connected with a yellow wire.

Its the one slightly lower down.

[flash22]

Quote

Denso - 89428-10120

or

Aisin - 89428-52010

Both cross to the same aftermarket parts

Quote

1.0 or 1.3 temp detect sensor - right rear of the head (as you look at the engine) it on an elbow at about 45º

The one for the ecu is 2/3 pin, the one for the warning light is single wire/pin (usually a green socket on the sensor

it's known by various names, it's a temperature Sensor - one is located in the thermostat housing the other is on the block

[beanbayli55]

On 7/31/2022 at 11:28 AM, flash22 said:

The one for the ecu is 2/3 pin, the one for the warning light is single wire/pin (usually a green socket on the sensor

it's known by various names, it's a temperature Sensor - one is located in the thermostat housing the other is on the block

update:   ok so i changed the other sensor today, the one with the single pin and its made no difference at all.

 

the light stays on still almost permanent  it may go off whilst driving for a minute or two then comes back on and stays on.  

everything is working as it should, the ecu is reading the temperature fine, it gets up to 93 degrees , the fan will come on , temp goes down to 85 then fan turns off.  both rad pipes get hot at this point so thermostat is working just fine

[flash22]

Unplug the dash and plug it back in, is it the analogue or the digital VFD type gauges ? Does it just stay blue all the time ?

[beanbayli55]

3 hours ago, flash22 said:

Unplug the dash and plug it back in, is it the analogue or the digital VFD type gauges ? Does it just stay blue all the time ?

hi i appreciate your replies, thanks.

 

what do you mean by unplug the dash?  the actual dash console?  i was thinking of doing this and disconnecting the Battery to reset the ecu just in case.  the light always stays blue or off, never red or does it ever overheat.

 

its this type of display:

 

 

[Derek.w]

The wire from temp. sensor feeds into dash have you checked its resistance back to the sensor use diode mode on meter just to make sure you dont have a high resistance.

I push a pin through the wire as far back as you can go without removing dash meter wires just extend them with a wire you can measure its resistance first expect it to be about the same.

Just put some tape around the hole you make in the wire.

[flash22]

yes the actual instrument cluster, knowing the gauges it's likely to be an in pin fitment issue/ oxidization a simple unplug/plug back in, is enough to clean the contacts

the surround is just clipped in place the instruments ar held by 4 screws

random vid off YouTube

 

[beanbayli55]

i disconnected the Battery for half hour this morning and during that time, pulled the dash and cleaned the connectors and on the bulb itself, gave the wires a little wiggle.

 

SO far its looking like its working again, it will go out now after a few minutes as it should and on a half hour drive it never came back on so fingers crossed its sorted.

 

thanks for all your help with this.