2001 TDI ALH Fuel Temp Sensor Troubleshooting - NewBeetle.org Forums
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  #1 (permalink)  
Old 12-29-2011, 03:17 PM
New Member
Join Date: Jul 2010
Springfield, MO, USA
Car: 2001 TDI
Default 2001 TDI ALH Fuel Temp Sensor Troubleshooting

Hi All,

This is more specifically related to my fuel temp sensor issue, so I started this new thread, my problem being initially stated in the thread titled "2001 NB hard to start, when warm runs great".

A quick recap-
Over the past couple months my car seemed to require more cranking to get it started than it used to. At the end of the work day on December 14, after the second cycle of the key and 5-6 seconds of cranking each time, it finally started, but as I drove off the CEL and blinking glow plug indicators came on. I checked with vag-com when I got home and the errors were:

2 Faults Found:
17970 - Quantity Adjuster (N146)
P1562 - 35-00 - Upper Limit Reached
16566 - Fuel Temp. Sensor A (G81)
P0182 - 35-00 - Short to Ground
Readiness: 1 2 0 0 0

And at this point the car would no longer start. The details of subsequent events are in the other thread, but the short story is I replaced the fuel filter, got the car running again after lots of cranking, then added some Power Service and topped off the tank with known good fuel. Have driven it about 350 miles since then and it runs fine. Still a bit hard to start but not as bad as right before the filter change. QA error cleared on it's own and has only come in once in the past week and that was during the start the day after Christmas after it sat for 48 hours. I had to crank for about 5-6 seconds before it started. QA error cleared on it's own the following day after three engine starts and has not returned. I still have the fuel temp sensor short to ground fault, but based on what I've read on these forums, and the fact I was having starting issues before I got the fuel temp sensor fault, I don't it is the cause of the hard starting. Still, it needs to be corrected.

I have read several procedure posts and looked at the pics on replacing that sensor. From all accounts, an easy fix, still, I'd prefer to do more troubleshooting to verify it is the sensor before opening the IP. Here are my questions:

1. Has anyone had this error and replacement of the sensor fixed the problem?

2 It isn't clear to me how the sensor is connected electrically inside the pump. I know it is held in with two small screws. What isn't clear is how the sensor itself can suddenly short to ground. After finding a fair amount of water in the old fuel filter, I thought perhaps some had gotten into the IP and caused the sensor to ground out. I thought this would maybe be a temporary fault and would clear once the water worked through or was dried by the diesel additive. But that hasn't happened, not yet, anyway. Has anyone ever had this error clear on it's own?

3. I understand it is possible to take ohmmeter readings on the sensor by disconnecting the electrical connector going to the IP. I'm sure that connector has never been apart on my car. Are there any tricks to getting it apart? Any "keepers" or clips, etc. that need to be disconnected first? Does it just pull apart?

4. I've seen tables of what the resistance of the thermistor should read at various temperatures as read from the two terminals on the connector. What should be the resistance from each terminal to ground? I would think that should be infinite on a properly working sensor, but would assume in my case that one or both would read low if the short to ground is at the sensor itself.

5. If I do replace the sensor, I assume when I remove the IP cover I'll lose prime again and will have a difficult time getting the air worked out similar to what I went through when I put in the new fuel filter. I'd prefer not to put that much stress on the starter, battery, etc. I've seen reference to the use of hand operated vacuum pumps to get the air out of the fuel system. Which pumps are recommended?

6. Are there any check valves in the fuel system to prevent the fuel from draining back to the tank, or is the design dependent on the entire fuel system remaining full of fuel when the engine isn't running, i.e. no air leaks? I searched through the Bentley DVD on the car and didn't see any reference to a check valve in the fuel system.

I'd appreciate any other tips not covered by these questions.

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  #2 (permalink)  
Old 01-04-2012, 01:52 AM
New Member
Join Date: Feb 2006
Aiken, SC, USA
Car: 2006 TDI and 2001 TDI

On my ALH I would prime the new filter after replacement with a handpump. Any of the hand pumps should work, I have a plastic mitivac from Harbor Freight, and used it for bleeding brakes and the filter. I always try to fill the filter with diesel, or atf the connect the handpump to the return line going to the tank (the inboard line). The system stays full, and if you have an air leak you will loose prime and have hard or no start situations. I had to cut the ends of the hose a little shorter and use screw clamps after the second or third filter change, about 120k miles.

I believe the resistance between the two leads is what you want to measure, there shouldn't be either of them grounded. I believe you need a triangle socket to open the IP, metalnerd or someone simillar has them I believe.

Let us know what you find when you take readings.
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Old 01-16-2012, 02:56 AM
TDI_bubble's Avatar
Join Date: Apr 2010

There is a special tool for opening the IP,
ALH Metalnerd Injection Pump Socket | Kerma TDI
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Old 11-29-2012, 04:15 AM
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Join Date: Nov 2012


About your hard starting VW TDI. In the fuel tank is located the fuel pickup filter and the fuel guage sending unit. The reason the car is hard to start, is this filter overtime gets plugged, making the fuel injector pump work very hard to draw fuel to the engine. You can access this assembly from inside the car. Remove the rear seat, you will see a plate w/ screws. Remove this plate, and you will see your fuel tank. Item is held in place with a large nut. Use a hammer and screwdriver to turn the locking nut counterclockwise. Once you see it, you will understand how to get it out. That was a problem concerning my 2001 VW Beetle. I had to crank it longer than normal for it to start. After I replaced that unit, the problem disappeared. Car only had 50,000 miles on it, but the car was also 11 years old. The old unit was really gummed up.
Good luck
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