Yaris mk1 1.3 overheating

August 2, 2020

Hi,i noticed in warm weather if in traffic or waiting, sometimes the red temp light comes on, if i drive on faster for a while it goes out.

I checked the coolant which was at max level in the tank, and the radiator fan was not coming on. I checked the coolant fan relays 1 & 2, they did click when tested externally with 12v. I also tried swapping them with the horn relay, but the coolant fan never came on despite switching dashboard AC on and blower on max. ( should the fan come on immediately with AC on ? ) With ignition sw off, I removed the two relays, I traced the radiator fan plug and it seemed to have 12v to one relay, and the -ve to the other one, so i test wired +12v & - ve into the two relay sockets from the Battery, the radiator fan came on, which i assume proves the motor and cabling is fine.

I am thinking the overheating engine is due to the radiator fan not coming on when it should. I thought i should to test the temperature sensor next, but i dont know where it is, can anyone advise what to do please?

( also i have another fault, the AC is warm air, has been for some years, i assumed it just needs a regas, and will not be affecting the cooling system ?)

PS my wife had the car since new, and some years ago i noticed one fan relay wasnt plugged in and was just loose inside the fuse box, i assumed it was a spare one, as the car was fully working. I didnt know it was fan relay at the time, this makes me think it was like that from new ? ! )

August 2, 2020

I'd say the overheating's definitely due to the rad fan not working. I doubt if it's the temperature sensor as the overheat light's working. May be worth using an auto-electrician rather than changing parts at random.

If the air-con's not been working for years due to a leak, then it's likely to have water vapour in it and may well not be worth repairing.

August 3, 2020

thanks for your response. Guess what? i have good news ! i tested everything again, and confirmed it should all work, (i didnt test the sensor as i dont know where it is) , so i concluded it was due to the 'spare relay' neverbeing plugged in from new !!!!

I plugged it in and ran the car to temperature, and hey presto the fan came in and out !!!!!!!!!!!!!!!!!

So it was all due to the Toyota Main dealer nobbling my car whilst in for service.

They had also given me a big nail in my tyre, and made the airbag light come on, and then quoted me £100's to fix these extra issues which suddenly appeared when they had the car.

I never went back there after that, but this relay was never noticed...

August 4, 2020

On initial read I wrongly assumed that the nail in the tyre had prompted the airbag light!

August 8, 2020

just drove it in hot weather all day, no issues 😎

R R G supplied the car, and although i have no proof, the relay was pulled, the tyre was nailed, and the airbag was loosened plug ( which i found and fixed a few years ago)