Been having a play with craigs S4 today, and decided to read off the fault codes, which highlighted a fault code for the coolant sensor:

17664 - Engine Coolant Temp Sensor (G62): Open or Short to Plus

However, the coolant sensor isnt that old, and appears to work perfectly

Viewing the measuring blocks on the ECU showed the sensor reading 19c (which was within 1c of the outside ambient temp), and upon starting the engine it sensibly rose to 92c over a few minutes of driving then fluctuated around there by a few degrees, exactly as you'd expect...

Cluster also works fine and reads as expected.

Anyone seen this before?


My only thaught its that its a G-box ECU, running D-box code, but the same G-box ran C-box code previously without any issues. Thinking back, the code appeared when we reshelled the car, which involved changing the ECU from C-Box to D-box code so it was compatible with the ESP on the '01 shell.

It just doesnt make any sense. If the sensor was shorted out like the fault code suggests, then it wouldnt be able to give perfect readings on the measuring blocks. They'd just default out to a standard value?

As i've said in the post though, the sensor readings are prefect.

The sensor cant be "open circuit or shorted to plus" as the fault code says, but then also give spot on accurate readings. If it was broken in the way the fault code describes, it would just be permenantly reading a default failsafe value.

If you clear the codes, does this error come back instantly?

When you unplug the sensor, the code should pop up as soon as you power up the ECU( turn the key).

What is the exact code number?

Just so you know, if you have a fully registered VCDS then you have free support from Ross-Tech.

Also the Ross-Tech Wiki has a list of DTC codes along with what could be causing the code and what to check to fix it.

Hope this helps.

This isn't exactly your problem, but just something I wanted to add. If you unplug the MAF sensor from a  MK4 2.0 VW engine it will still show values in the measuring block in g/sec just like it would if it were plugged in. The same with the intake air temp (which also happens to be in the maf sensor on this particular engine). For sure on newer models if you unplug a coolant or intake air sensor, it will default to -42 c or some other completely unachievable number to show there is no sensor info available. Looking forward to see what happens when you unplug the sensor..Is it also possible it can get this info from the other coolant sensor(s) mounted on the lower coolant hose?

Maybe just unplug the cluster?

I would change out the sensor first thing if I was sure there wasn't a short in the wiring itself. The part is only like 9 dollars, and you can just take it back if you need the money. You don't even need to to install it, just plug it in and check for DTCs! While its out in the air see if the sensor shows the same temp as the ambient air temperature by comparing the values to a thermometer.
 
So I'll ask again...what DTC code are you getting??

The point with Ross-Tech is if you have a registered version, they will help you diagnose the problem. Go on their forum and post a full scan. They won't give you the time of day if you are using the unregistered version with a cheapo "Ebay" interface. 

If none of this works, reflash the ECU to the file you had before your current one to see if it is indeed the software. I highly doubt the software is the issue though.

Yes! I remember reading about this in the VWVortex forum! Because the thermostat was malfunctioning, the coolant sensors were "out of sink" so to speak with each other. The ECU knows what both sensors should read at certain coolant temps and if the ratio of the temperature reading of the coolant sensor in the radiator compared to the coolant sensor in the coolant flange (bolted to the head) are off, things get screwy...