just scanned my car and it's been suffering for ~ 2~3 months on CEL with error code :

17704 - Error in Mapped Cooling System (check Temp-Sensor and Thermostat) P1296 - 35-00 - -

thermostat is working fine... so it seems to be the green 4-pin temp sensor

wires seem to be ok, and i have been spraying them with contact spray the last day and error still holds after clearing

heard from some fellow working at skoda that the second coolant sensor (2 pin grey near the radiator) can be causing the problems. maybe he is not quite on the subject as i heard the second temp sensor commands the secondary air system...

been having some semi-lump modes lately, but temp gauge was always stable...

my fan relay opens at 80 celsius measured on vag-com. is this correct ?

am i right to think the 4-pin temp sensor is on it's way out ?

Edited 17 September, 201114 yr by za_killer

If the green CTS is non VAG there's a good chance that it's faulty on the ECU send pins. Green VAG CTS doesn't usually fail, but I know of several people who bought Ebay & GSF CTS's that have failed.

BTW. If you have VAGCOM you can see what temp the ECU is getting from the CTS, & compare it with what the temp gauge is reading.

gauge is reading 90 while temp sensor sends from around 72 to 80... 80 starts the fans so it does not go higher than 82

not sure if it's a genuine one, as it was already fitted when i bought the car

btw, we're talking about a 2004 vRS, and if a interpret correctly it should have had the green (new revision) CTS as it exited the factory, or ?

Post 2003 VAG 1.8t's should have the revised green CTS. For your info. The green CTS has 2 seperate sends, 1 to the temp gauge & the other to the ECU. If the ECU is getting incorrect temp it won't be fueling correctly hence lumpy idle. The grey rad sensor operates independently of the CTS.

Post 2003 VAG 1.8t's should have the revised green CTS. For your info. The green CTS has 2 seperate sends, 1 to the temp gauge & the other to the ECU. If the ECU is getting incorrect temp it won't be fueling correctly hence lumpy idle. The grey rad sensor operates independently of the CTS.

thanks for the help

on a side note, i was trying to find out if the temp values my ECU received were correct based on the readout of the temp gauge :p

CTS doesn't normally cause the ECU to throw a code unless there's an open circuit, so it may be that you have a wiring fault. If your temp gauge appears to be acting normally then the likely problem is on the CTS ECU feed.

now that you mention it, been drawing a graph to see the temp fluctuations on the CTS ECU sensor. while engine was on the values were stable; as engine was off, the temp dropped several times to ~14 than came back to normal.

have read a thread here with someone getting the same error code and replacing the temp sensor to fix it (and actually worked)...

only one thing left to do: measure the inner resistance of the CTS, if it turns out to be fine there's a wire problem, otherwise it's time to change it

now that you mention it, been drawing a graph to see the temp fluctuations on the CTS ECU sensor. while engine was on the values were stable; as engine was off, the temp dropped several times to ~14 than came back to normal.

have read a thread here with someone getting the same error code and replacing the temp sensor to fix it (and actually worked)...

only one thing left to do: measure the inner resistance of the CTS, if it turns out to be fine there's a wire problem, otherwise it's time to change it

Yep you're on the right track.

measured the CTS, turns out it was on it's way out. went and bought a new one for ridiculous 35 euro, installed it, slammed vag-com on my car and cleared the code. left the engine running to see if code still pops up, it didn't, so all was right.

while doing a graph to see at what temp the fans kicked in i saw a huge difference

-with old CTS: fans kicked in at ~82

-with new CTS: at ~98

so i have one last remaining question: is the desired temperature 98 ?

I had same fault a few weeks back. Changed to new green CTS. No more faults. Checked the temp with vag com and IIRC 90 degrees on temp gauge was showing 93/95 degrees on vag com. So I would imagine 98 is about right for fans to come on. Incidently, since changing mine I have less of an overboost. The car seems smoother and the power seems to come on at 2K rpm instead of 1750 ish like it used to.