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Blue temp light stays one 24/7

13520 Views 46 Replies 5 Participants Last post by  billymade
Ok guys don't scream at me, just spend two days looking at forums etc.
So I got a 2001 gls beetle for $700, the reason so cheap is it burns a little oil. (Read that's normal, and the blue temp light stays on 24/7). The car has 140k on it. Timing bet, water pump, etc has been done at a dealership in Dallas at 122k (have the paperwork).

So I don't have the vag tester I am pretty handy with other tools, I have a ir gun and temp prob. We get the car home no issues, I start to look into the issue in the morning car runs cool. Would get to about 150-160 I measure this at the coolant temp sensor. Read that's the thermostat, pulled it out while car was still a little warm it was still open slightly. Boiled it, opens to early. Replaced it burped the system drove all over. The car highest temp was about 205ish, blue light still on 24/7. Read next it could be coolant level sensor, read to jump it. Blue light stayed on then started flashing red. Not sure what that was all about, that or jumper fell out should of double checked that. So to me that sensor is working, got a new coolant temp sensor, one in the car is green new one from autozone is black. Replaced it and topped off coolant drove the car no change blue light on 24/7.. The system seems to be work fans come on around 187ish. I want the light off lol! I read something that says to measure the sensor but it called pins 1-4 my sensor and plug are labeled abcd.

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Also no check engine light at all.. So I can't pull any codes correct?
Not true. Just because the light isn't on doesn't mean there aren't codes. Get it scanned and see what comes up.
When to autozone, pulled codes no code found.
The temperature sensors have a high failure rate. When mine went bad the blue light would turn on and off intermittently even when the car was fully warm. It is the sensor in the coolant flange that has a 4 conductor connector.
I've replaced the sensor, no change light just stays on.
My car did this; when one of the wires broke off the end of the terminal, I replaced the terminals and the plug; the problem went away. I would think that your wiring and or plug to the sensor, is compromised, check your wiring and see if everything is okay.

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Replace it with a VW OEM sender from the dealership.
Any one have a wire diagram of the system? I know it's a two part system on reports to ecu and other runs the temp light. Correct? I would like to figure which one runs the dash so I can jump it to test if that's the circuit compromised. I believe the old cts is from the dealer and I still had the same issues.
Ok so I don't have the vag tool. I jumpered 3-4, should the dash light go red? Anyone know what each wire does? I know 4 is ground but which one turns the blue light on and off? Should I do a reset on the computer? Unhook battery for about a minute them touch + & - to discharge any voltage, them turn key on for about a min? Does the computer store the data? I'm lost.. Side note today it started flashing
Did you do the testing procedures in the service manual? Here are where the pages start; the testing/troubleshooting sequences without a factory scan tool ( obd II/multimeter: advance the pages for more steps):

Volkswagen Workshop Manuals > New Beetle GLS L4-2.0L (AVH) (2001) > Engine, Cooling and Exhaust > Cooling System > Engine - Coolant Temperature Sensor/Switch > Coolant Temperature Sensor/Switch (For Computer) > Component Information > Testing and Ins
Any updates? :confused:
Well I jumper 3-4 on the plug, I dont have the correct tools to see if the temp goes to 140C. but from what I understand the light should of went red (over heating). At this point I dont have wire schematics so in that troubleshooting guide I dont know where a few points they point too are. I think its wiring/ecu, I may order an ecu from a site that allows returns for any reason. I guess ill just throw parts at it. I started trying to trace out where the wires go, but dont want to cut up the factory harness. if I had schmatics i would try to ohm the wiring (point to Point). see if there is a break somewhere.
Do you have a scanner with live data and/or a multimeter; to read the temps/check the wiring? Pretty much all the testing procedures are in the link and later pages in the online vw service manual. Did you inspect the wiring and see if anything was damaged and use your multimeter, as per the manual and test/troubleshoot the wiring? :confused:
Do you have an Android phone?

Also, before you do anything else... read post #8 again. I highly recommend it.
Ok I'll retry the old unit it was about a year old and no I have a iPhone why?
Because an android device can run the Torque app and connect to a $15 bluetooth OBD2 adapter. You get a full function scanner, logger, and code reader for free. Find a buddy with an Android phone or tablet.

I use this one:

I know I sound like a broken record... but... try a new sender from the dealer.
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My local pick n pull was having a 50% off day so I snagged a ecu for 12.98 from an identical car with same options. So I'll swap it tomorrow and try it again. Pray all goes well. I also ordered a scanner like yours we have a tablet that it will work on.

Ok so just did more reading sounds like it won't be as easy as putting the ecu I'm the car and running it to see if that fixed the issue. I think if I put it in I'll be hit with the immobilizer... Fml am I right?
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