When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
It's my first post and unfortunately it's a problem I can't seem to get rid of. So today I got a warning saying "high coolant temp, run vehicle whilst stationary" this didn't fix it. I checked coolant level and it was slightly under min so I topped it up with some water as had no spare coolant. This didn't work either and engine temp was still on max.
Left the car off for nearly 5 hours and then started it up and the engine temp is still showing max.
Could it be a faulty temp sensor? I'm hopeful it's a simple fix as had no prior warning to indicate low coolant level.
Worst part is cars just 3 months out of warranty. Knew I shouldn't have extendedy lease beyond the warranty period 🤦♂️
Could be a temp sensor, could be a pump not circulating coolant, could be a thermostat not passing coolant to the radiator, could be the radiator fans not coming on (the fans are only relevant at idle and slow speeds, at highway speeds the fans do not assist air volume through the radiator).
You say B9, is this an A4, A5, Q5. I wonder if the vehicle has the radiator shutter system; maybe the shutters are not opening.
Do you have VCDS or such so you can scan for DTCs? If you can't scan for codes from the car's many computer modules, you're working blind. A generic OBD-II scanner is not a final word on codes; you need something known to be able to directly read DTCs from all online modules (VCDS, OBDeleven, etc). But an OBD-II generic mode scan might still give you something.
I say a scan tool because it would be better if you could actually read the live oil and coolant temps. Is the coolant temp starting off at ambient at a cold start? Does it climb as expected over the next 5-10 minutes to 90°C+, does it sit there for a while then go upward, or go straight on upward, or does it jump irregularly from low to high? What is the oil temp doing during this? The oil is cooled by the coolant; is the oil temp maintaining or also climbing? Etc. And there's usually two coolant temp sensors, the one on the engine (G62) and the one on the radiator outlet (G83, so temp after the coolant has passed through the radiator). What is that G83 temp doing in contrast to the G62 temp?
"Left the car off for nearly 5 hours and then started it up and the engine temp is still showing max." 5 hours is ok, but I'd be more interesting in a 12hr+ outage. It could be wiring or the sensor. Checking the workshop manuals, if you pull the plug on the sensor and measure the resistance across the pins of the sensor, it should register 2250±750Ω at ~20°C (so after it's not been started for a good overnight at least). Checking the wiring is more complicated as you'd need to disconnect the plugs from the engine control module to get to the pins on the other end of the wires.
Could be a temp sensor, could be a pump not circulating coolant, could be a thermostat not passing coolant to the radiator, could be the radiator fans not coming on (the fans are only relevant at idle and slow speeds, at highway speeds the fans do not assist air volume through the radiator).
You say B9, is this an A4, A5, Q5. I wonder if the vehicle has the radiator shutter system; maybe the shutters are not opening.
Do you have VCDS or such so you can scan for DTCs? If you can't scan for codes from the car's many computer modules, you're working blind. A generic OBD-II scanner is not a final word on codes; you need something known to be able to directly read DTCs from all online modules (VCDS, OBDeleven, etc). But an OBD-II generic mode scan might still give you something.
I say a scan tool because it would be better if you could actually read the live oil and coolant temps. Is the coolant temp starting off at ambient at a cold start? Does it climb as expected over the next 5-10 minutes to 90°C+, does it sit there for a while then go upward, or go straight on upward, or does it jump irregularly from low to high? What is the oil temp doing during this? The oil is cooled by the coolant; is the oil temp maintaining or also climbing? Etc. And there's usually two coolant temp sensors, the one on the engine (G62) and the one on the radiator outlet (G83, so temp after the coolant has passed through the radiator). What is that G83 temp doing in contrast to the G62 temp?
"Left the car off for nearly 5 hours and then started it up and the engine temp is still showing max." 5 hours is ok, but I'd be more interesting in a 12hr+ outage. It could be wiring or the sensor. Checking the workshop manuals, if you pull the plug on the sensor and measure the resistance across the pins of the sensor, it should register 2250±750Ω at ~20°C (so after it's not been started for a good overnight at least). Checking the wiring is more complicated as you'd need to disconnect the plugs from the engine control module to get to the pins on the other end of the wires.
Firstly thanks for the detailed response. Its a 2019 B9 A5 2.0TFSi.
As you've mentioned I've used a obdeleven to run diagnostic checks and access live data as I don't have access to VCDS. I've attached pictures showing coolant temp at both the radiator (22.5) and engine (126.2) outlets. It seems its a faulty temp sensor at the engine end. I forgot to check the oil temp. I only ran the car for 5 - 10 mins as I nearly froze to death in the cold 😅
So I started the car after 12 hours and the temp gauge is still stuck on max and after a few minutes the warning "coolant temp too high" comes up
I'll have to get a mechanic involved to measure the resistance etc as I haven't got the tools. I'll test it again and the car upto temp and get all readings again.
I've attached fault codes that I found. Bear in mind that the car is booked in for recall work as it needs a new starter/alternator and the faults are related to this.
You'll probably find a thread about the G62 sensor if you look in the B9 A4/A5/Q5 forums. For the CYMC, it's on the back of the cylinder head, iirc. https://www.europaparts.com/coolant-...79919523j.html Should be simple enough to replace yourself if you do DIY at all.
You'll probably find a thread about the G62 sensor if you look in the B9 A4/A5/Q5 forums. For the CYMC, it's on the back of the cylinder head, iirc. https://www.europaparts.com/coolant-...79919523j.html Should be simple enough to replace yourself if you do DIY at all.
I have a feeling it is the G62 sensor from the readings I've posted in my last message as you you've mentioned. Something I'll probably have a go myself. Any idea if there's a B9 guide on how to change it?
There's the workshop manuals direct from Audi, which any DIY attempter should always have. erwin.audiusa.com, pay for a day, get all the PDFs for your VIN. This would be in the Engine "one"; Audi split the engine stuff into two manuals for who knows why some time back.
You could try the docs at cardiagn as a fallback if you don't plan on working on your car often. They are there, they are not the latest revs, and it's more annoying to use and open than just having a local PDF doc. But they're there.
Otherwise, I'm sure google searching for replacing the G62 on the CYMC should find something.
02-05-2023, 08:02 PM
HELP! My B9 is showing High Coolant Temp warning
