Faulty coolant temperature sensor?

[dmjw01]

Do I have enough evidence to convince a dealer that the coolant temperature sensor on my Ibiza FR TDI is faulty? The symptoms are:

1. Fuel economy has not quite improved as much as I'd expect now that the ambient temperature has picked up after the winter. It's maybe 4 or 5 mpg down on what I'd expect - particularly for short/medium journeys.
2. Glow plug light still stays on for at least 5 seconds when starting from cold, even when ambient temperature is above 10C.
3. After waiting for glow plug light to go out, the engine starts with slightly more revs than normal. It revs to about 1400 rpm before settling back down to normal idle speed. Warm starts are normal - GP light goes straight out and engine starts at normal revs.
4. If I plug in VAG-COM before starting and the engine has been off for many hours, the coolant temperature sensor often disagrees with the ambient temperature. For example, a few days ago it was 15C but the coolant temperature said minus 1.8C.
5. Coolant temperature reads a sensible figure when the engine is hot - about 86C or so.
6. The other night I was running the engine in Group 11 Basic Settings to exercise the VNT mechanism (I do this whenever I've been stuck in traffic jams in the last few days), and the dashboard temperature gauge was moving up and down.
7. A couple of weeks ago I had a fault code: "17664 Engine Coolant Temp Sensor (G62): Open or Short to Plus P1256 -35-10 - - - Intermittent". But foolishly I reset this code and it hasn't come back, so I've lost the evidence.

Has anyone had experience of a faulty coolant temperature sensor - are the dealers likely to accept that there's a problem, even though the performance of the engine is normal (except perhaps the marginal mpg degradation)?

[micky 32]

yep , faulty as hell

[dmjw01]

Thanks.

On the way home today, I had to stop at some lights when the engine was half-way warmed up. After idling at the lights for a minute or two, I noticed that the gauge was down at the bottom; but then after pulling away it moved back up again. It's definitely not right.

I'll give 'em a call on Monday morning!

[muddyboots]

Before taking it to the dealer - if you know where the sensor is, you could pull the connector off to trigger the fault, then reconnect

[dmjw01]

Originally Posted by muddyboots

Before taking it to the dealer - if you know where the sensor is, you could pull the connector off to trigger the fault, then reconnect

Good idea! But fortunately there's no need for crafty subterfuge - the fault code has come back today, just in time for it to go to the dealer's on Thursday!

[tune-tec]

Just came across your post, what was the oputcome of that P1256 17664 eror code, have the same on Audi A4 1.9TDI 130BHP, coems up as sporadic. Is it as simple as changing the coolant sensor?

Thanks.

[lard44]

And sorry to hijack the thread - but on the tdi 130pd isn't the temperature sensor inside the coolant bottle? I've been meaning to change mine.

Sounds like they should have recalled these they're so faulty...

[dmjw01]

It was replaced under warranty.

VAG-COM helped, because I was able to record the temperature (measured by the faulty sensor) as the engine warmed up. I plotted a graph using Excel and this clearly showed the temperature going up and down in big peaks and troughs. The bloke at the dealership looked at me like I was from another planet.

[peteTDI]

Originally Posted by lard44

And sorry to hijack the thread - but on the tdi 130pd isn't the temperature sensor inside the coolant bottle? I've been meaning to change mine.

Sounds like they should have recalled these they're so faulty...

no it's on the end of the head gearbox end

[muddyboots]

Originally Posted by dmjw01

I plotted a graph using Excel and this clearly showed the temperature going up and down in big peaks and troughs. The bloke at the dealership looked at me like I was from another planet.

LOL, dealers hate it when people show more technical ability than they do

Coincidentally I noticed a fault code relating to the coolant temp sensor on mine the other day...

[lard44]

Originally Posted by peteTDI

no it's on the end of the head gearbox end

Cheers - but I'm still struggling to find it - anyone got a pic or a link? TBH I've been meaning to change this for ages but never got around to it...

Feel free to patronise and break it into really small steps if you like...

[digby130?]

Originally Posted by lard44

Cheers - but I'm still struggling to find it - anyone got a pic or a link? TBH I've been meaning to change this for ages but never got around to it...

Feel free to patronise and break it into really small steps if you like...

i know this is a really REALLY old thread, but does anyone have diagram showing this sensor as i think i have the same problem haha!

[Philip Reynard]

Originally Posted by dmjw01

Do I have enough evidence to convince a dealer that the coolant temperature sensor on my Ibiza FR TDI is faulty? The symptoms are:

1. Fuel economy has not quite improved as much as I'd expect now that the ambient temperature has picked up after the winter. It's maybe 4 or 5 mpg down on what I'd expect - particularly for short/medium journeys.
2. Glow plug light still stays on for at least 5 seconds when starting from cold, even when ambient temperature is above 10C.
3. After waiting for glow plug light to go out, the engine starts with slightly more revs than normal. It revs to about 1400 rpm before settling back down to normal idle speed. Warm starts are normal - GP light goes straight out and engine starts at normal revs.
4. If I plug in VAG-COM before starting and the engine has been off for many hours, the coolant temperature sensor often disagrees with the ambient temperature. For example, a few days ago it was 15C but the coolant temperature said minus 1.8C.
5. Coolant temperature reads a sensible figure when the engine is hot - about 86C or so.
6. The other night I was running the engine in Group 11 Basic Settings to exercise the VNT mechanism (I do this whenever I've been stuck in traffic jams in the last few days), and the dashboard temperature gauge was moving up and down.
7. A couple of weeks ago I had a fault code: "17664 Engine Coolant Temp Sensor (G62): Open or Short to Plus P1256 -35-10 - - - Intermittent". But foolishly I reset this code and it hasn't come back, so I've lost the evidence.

Has anyone had experience of a faulty coolant temperature sensor - are the dealers likely to accept that there's a problem, even though the performance of the engine is normal (except perhaps the marginal mpg degradation)?

I have ibiza 1.2 copa ST new 2011 under the Motability scheme and this winter has same fault as yours. Dealer cannot find fault as 15 mile drive from my home and car is fine after 8 to 10 miles running. Problem only in cold weather and not winter 2011/2012. I have finally convinced my dealer to have car overnight next Monday 4th March so they can run from cold start. I just hope Monday is a cold night and fault located as is warranty issue in my case and I had to get Motability to put pressure on dealer and supply hire car. I will let you know the outcome and hope it will help you in your quest. Regards, Phil

[Philip Reynard]

Originally Posted by Philip Reynard

I have ibiza 1.2 copa ST new 2011 under the Motability scheme and this winter has same fault as yours. Dealer cannot find fault as 15 mile drive from my home and car is fine after 8 to 10 miles running. Problem only in cold weather and not winter 2011/2012. I have finally convinced my dealer to have car overnight next Monday 4th March so they can run from cold start. I just hope Monday is a cold night and fault located as is warranty issue in my case and I had to get Motability to put pressure on dealer and supply hire car. I will let you know the outcome and hope it will help you in your quest. Regards, Phil

Dealer said no fault. Motability paid for new coolant sensor. Car now perfect again. I believe Seat are avoiding this issue. Regards, Phil

[Pimped up vario]

I know this isn't a dealer moan thread persay but I couldn't help but share as dealers are in the posts.

The guy in charge of mervyn stewart parts/servicing department tried to swear blind to me that the car didn't have an open thermostat problem and that my model of skoda didn't come with rear door card speakers. The rear door card speaker was missing after they had replaced a failed door seal.

I told him to wise the bap and get the thermostat replaced and told him to go look at the right hand side of the car.

What's worse is that when it came to light that I was right and he was wrong was that there were no red faces on his part or no apologises for his verging on rude attitude.

What VAG-COM did you use to do that work, if you don't mind me asking. I have a gendan lead and rosstech vcds lite but haven't really had the time or weather to get to grips with it. No garage you see and laptop battery is dead. You're not allowed to use an invertor with the lead.