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Undefined Fault P1293 - Thermostat Short to Plus

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VWAffe View Drop Down
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  Quote VWAffe Quote  Post ReplyReply Direct Link To This Post Topic: Undefined Fault P1293 - Thermostat Short to Plus
    Posted: 22-Feb-2008 at 00:26
Minor update:

Since everything worked fine for a few days, I took the car on a 750-mile trip to FL this week. I'm actually still there, and will head home tomorrow. The T-stat worked great the first 400 miles, until I shut the car off and stopped for gas, after which it refused to be electronically controlled, and temps climbed rapidly, but stayed stable depending on the load.

I was having a bad day. Shortly before stopping for gas, I got my first speeding ticket in 5 years, to the tune of $220.50 for 74 in a 60 - by accident no less. I was keeping it below 67 indicated, not using cruise while passing through a town in LA, but my foot must have twitched... at the wrong time. Why not throw in overheating to top it off?

The good news is that the failsafe mode works. I was able to limp along, nursing it and monitoring the temps in real time via VAG-COM, not exceeding 65mph to keep the temps below 108C. That's almost 230F, at which point the needle just starts moving up off of "normal" 190F on the gauge - not that I recommend finding out this way! BTW, it firsts rests on normal 190F at 73C... so the gauge tells you you're normal between 163-230 F! No other warnings came on, so I kept driving slowly, trying to imagine I was an uninformed driver who only knew that the catch-all check engine light was on and the gauge showed normal temps... not easy to do, but I didn't have much choice.

I also discovered that if you're logged in to the ECU in VAG-COM, the measuring blocks continue to monitor the sensor readings after you switch off the ignition... which allowed me to observe a screwball behavior: without fail, the T-Stat reverts to normal operation as soon as the car is switched off and the ignition key is removed. It opens right away, and within a minute or two of stopping, the car equalizes its temperature and works fine while shut off (after-run pump works!)... WTF?

After 200 miles of this nonsense and a few stops to observe the screwy behavior above, all of a sudden the t-stat started working again while I was moving, and never faltered again that day. Needless to say, I didn't stop again until my trip was over!

The last two days, it's been up to its tricks while I've been here driving around town, but tonight in between getting back to the hotel and going to dinner, it works again! Aargh!

When I get home, the beast is coming apart for sure. Because of the off-behavior, I'm feeling the ECU may be involved. I'm praying it works all the way home this time...

Edited by VWAffe - 22-Feb-2008 at 06:29
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  Quote BlueSteW8 Quote  Post ReplyReply Direct Link To This Post Posted: 22-Feb-2008 at 10:44
That is most unfortunate, Nate.
A shame that you are down to two very expensive parts to replace - the thermostat runs about $450.00, God only knows what a new ECU would cost.

*edit - Thermostat was $491.62 p/n # 07D-121-111-AB, there are also other parts om my repair order, but I'm not sure which seals/ gaskets are thermostat related v. cam adjuster related.
Labor to "Replace thermostat housing and reseal coolant" was $165.00

Edited by BlueSteW8 - 22-Feb-2008 at 19:32
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  Quote VWAffe Quote  Post ReplyReply Direct Link To This Post Posted: 23-Feb-2008 at 01:32
There could always be a wire fault, but I doubt it. A new T-stat can be had for about $380 - try a part # search at Rey Reese VW - they take internet orders and sell at wholesale... ~20% off the MSRP. For small orders, shipping cost is an equalizer, but you can save a lot on high $$ parts.

If I need an ECU, I'll try to find a used one. I need a good excuse to buy a Vag-Tacho setup, anyway. ;P

BTW - the car ran beautifully today. No problems whatsoever.
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  Quote BlueSteW8 Quote  Post ReplyReply Direct Link To This Post Posted: 23-Feb-2008 at 12:51
My parts were paid for by NESNA (Nissan/Infiniti extended warranty), as was the labor.
So, I wasn't too worried about it.
I'll bookmark Rey Reese VW for future reference.
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  Quote VWAffe Quote  Post ReplyReply Direct Link To This Post Posted: 24-Feb-2008 at 00:35
Quick update: I drove the last 250 miles home today with multiple shut-downs when I made a pit stop halfway home to shop for my wife's "souvenir". Only once did the car hiccup, but it wasn't the "short to plus" thermostat code, but rather a P2181 "performance malfunction in cooling system".

This is the one where the fans go nuts, and the climatronic diagnosis mode engine temp display shows an instant jump to something catastrophic like 130 C. Mine read 127 C a second after reading 89 C... so I plugged in the computer (had it at the ready, mind you) and pulled up good old group 131. Everything looked fine, but the thermostat was at 100% duty cycle, and the engine was cooling down way below specified value - so it was open. I looked at group 132, and there the radiator outlet temperature was showing higher than the engine temp. Odd... but I don't think it's the first time that's happened - just the first time I had the laptop in the car and ready. I saved the DTC, then cleared it, and everything went back to normal at once.

Screwy, and now that I'm home I want to pull it apart even if it takes a few evenings to figure it all out... but yesterday the inside pads of the rear brakes on my wife's Passat barely started hitting metal. So... I've got to take care of that first while she ferries kids around with my car. I'll be driving my old IDI F-250.

Edited by VWAffe - 24-Feb-2008 at 06:39
'03 W8 Sedan 6MT     ..."it goes to 11!"
'02 V6 Wagon 4Mo 5MT (Swap In Work)     ...both black on black w/ limo tint
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  Quote BlueSteW8 Quote  Post ReplyReply Direct Link To This Post Posted: 25-Feb-2008 at 11:23
Maybe try replacing the temp. sensor for the radiator outlet?
A cheap/ easy part to replace, and if it is sending a bad signal to the ECU, could that be causing it to mess with the thermostat duty cycle?
Perhaps even change both sensors?

It seems odd that it would detect such a wide swing in temperatures: 89C to 127C in a matter of seconds?
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  Quote VWAffe Quote  Post ReplyReply Direct Link To This Post Posted: 25-Feb-2008 at 15:53
The temp swing is consistent with either a short or an open circuit... I can't remember which right now since I don't have the manual open. What's weirder is that is is able to be "fixed" by clearing fault codes.
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'02 V6 Wagon 4Mo 5MT (Swap In Work)     ...both black on black w/ limo tint
'14 JSW TDI 6MT
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  Quote straightw8 Quote  Post ReplyReply Direct Link To This Post Posted: 01-Jul-2008 at 23:22
Bump for a question:

So what happens when the T-stat fails? will it damage the engine by preventing coolant flow, or will it fail towards "open" and keep everything safe? (besides codes, faults, and fans running constantly..)

what's the chain of events that is typical of a t-stat failure?
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  Quote fico Quote  Post ReplyReply Direct Link To This Post Posted: 13-Mar-2009 at 16:46
Originally posted by VWAffe

The temp swing is consistent with either a short or an open circuit... I can't remember which right now since I don't have the manual open. What's weirder is that is is able to be "fixed" by clearing fault codes.


Have you ever figured this one out? I got that same P2181 code today with fans running like crazy. by clearing code everything went to normal.Drove it to dealership and they checked with VAG all was working properly.
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  Quote tripwalking Quote  Post ReplyReply Direct Link To This Post Posted: 07-Apr-2010 at 16:42
I'm keeping an eye on this thread too... what happened in the long run?
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