1.9 TDi quattro - Temp at 70 , hesitates at 2000rpm, fan runs on.

[seanogrady]

I have a 2003 (53) 1.9 Tdi Quattro Sport. Recently, three separate problems have started to appear that may or may not be related, you may be able to help me;

Temperature gauge on the dash only rises to 70 degrees and no higher. However, it does not fluctuate.
When accelerating, in any gear, the engine hesitate slightly at 2000 rpm or just over.
When I switch off the ignition and get out of the car, the fan continues to run noisily and has never done so before.
All three of these issues started almost simultaneously. I have read many other threads with similar issues (but not all three) and I suspect I may need to start with changing the coolant temperature sensor, is this correct?

Thanks in advance for your help.

[kite]

Yes change the CTS its always s good place to start

using tapatalk from my phone

[benjie]

I'd change the thermostat too, it's cheap and relatively easy to do - if it's not been changed before, it's prob gone. My car hesitates at 2k rpm too (I have the same car as you) I'd love to know what it is.

[seanogrady]

Update - I bought a Vag-com cable from Gendan and here are the results using VCDS from Ross Tech:

VCDS-Lite Version: Release 1.1
Monday, 30 January 2012, 19:15:04.

Chassis Type: 8E - Audi A4 B6/B7
Scan: 01,02,03,08,09,0F,11,15,16,17,18,36,37,45,46,55,56 ,57,65,67,69,75,76,77

-------------------------------------------------------------------------------
Address 01: Engine Labels: 038-906-019-AVF.LBL
Controller: 038 906 019 LJ
Component: 1,9l R4 EDC 0000SG 4910
Coding: 00003
Shop #: WSC 63351
VCID: 6AA741AB0571
WAUZZZ8E24A055273 AUZ6Z0C0200073
1 Fault Found:
17663 - Engine Coolant Temp Sensor (G62): Short to Ground
P1255 - 35-10 - - - Intermittent
Readiness: N/A
-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 8E0-614-517.LBL
Controller: 8E0 614 517 A
Component: ABS/ESP allrad 3429
Coding: 04255
Shop #: WSC 06435
VCID: 263F759BD1E9
1 Fault Found:
00526 - Brake Light Switch-F
36-10 - Open Circuit - Intermittent


I've ordered the coolant temp sensor from Murrays Direct so will let you know how I get on. Hadn't noticed any problems with the brake light switch but I'll keep an eye on it.

[benjie]

The coolant temp sensor will cause the fans to run. Maybe to stick on 70. Get that changed first. If it still sticks to 70, change the thermostat. Brake light switch is easy to change, 5 min job and quite cheap.

I'm wondering if the slight hesitation may be the tandem pump struggling - is your engine bay greasy/gunky. I'm not too sure about that though, just a theory. Car is in the garage as we speak having a cam belt and they're going to investigate the tandem for me.

[pauldazzle]

Could be the CTS that's causing the hesitation as it feeds the ECU as well as the temp gauge. ECU will not fuel correctly if it's seeing the wrong temp from the CTS. A genuine VAG CTS is a must, do not buy an aftermarket CTS as they normally don't last long or just don't work straight off.

[seanogrady]

Right, I went for an original Audi sensor and spare clip (I broke the existing one at first attempt of removal!). I changed the sensor on Friday morning and topped up the coolant with G12++. Took the car for a spin of about 15 mins, the hesitation seems to have gone and the fans no longer run on after I switch off the engine. The only thing is, although the temperature went above 70, it didn't reach 90 and stay there. Admittedly it was -1 degree ambient temperature so 15mins on slow local roads might not have been enough to reach temperature. I haven't had a chance to go out in it since so a road test on the M25 to work it is!! I'll let you know how it goes before deciding to replace the thermostat.

[pauldazzle]

With the cold temp at the moment it will take a lot longer for a diesel engine to get up to 90. You need to make sure you haven't got an air lock though as this will cause erratic temp.
Put the heater on full hot, & with the header tank cap off start up & hold the RPM's up at about 2500rpm until the temp gauge has hit 90 for about 5 mins. Turn off & leave the engine to cool down, then check the coolant level, & top up if needed.
See how it goes for a few days, but if it still doesn't ever get up to 90 you'll need to change the thermostat as it's probably stuck open.

[BAZ911]

With the cold temp at the moment it will take a lot longer for a diesel engine to get up to 90. You need to make sure you haven't got an air lock though as this will cause erratic temp.
Put the heater on full hot, & with the header tank cap off start up & hold the RPM's up at about 2500rpm until the temp gauge has hit 90 for about 5 mins. Turn off & leave the engine to cool down, then check the coolant level, & top up if needed.
See how it goes for a few days, but if it still doesn't ever get up to 90 you'll need to change the thermostat as it's probably stuck open.
My A4 is a 2 ltr FSI with the same problems, temp has allways been low on gauge with poor output from heater, plus last week the fan has been staying on. Not sure about the diesels but I have been told that the petrols have an electric thermostat which is tucked away at the back of the head apparently the operating rod can come off. I have tried to find a diagram but have not been able to so far. I am going to change the coolant switch and work from there. If anyone has got a diagram of the thermostat could they post it up. Cheers Baz

[pauldazzle]

I'd say you have a stuck open thermostat.
Coolant temp sensor failure will not cause low heat from the heater, but can cause the fans to stay on.
Never heard of an electric thermostat on a VAG car.