1998 Jetta TDI, P1247. Needle lift sensor open or short to power.

[lmorris]

My son picked this beast up from a buddy to drive around, he recently had his ride written off. It has no boost and keeps setting P1247. I have access to Prodemand and have checked resistance of the needle lift sensor, 83 ohms. Spec is 80 to 120. Checked for voltage to the sensor and get 5 volts using battery ground. I get 3.2 volts when using the PCM ground. I read it was supposed to run 3.2 volts from the PCM. Checked all connections and found no issues. The diagnosis ends with replacement of the PCM. Given this is a free vehicle, we don't want to start throwing expensive and hard to get parts at this thing. My son is content with putting up with the lack of power, but I would like to try and fix it, if possible. If anyone has any VW Diesel experience, I would appreciate any input. Thanks.

[JoeR]

The #1 most likely cause is a bad injector, but all kinds of things can cause that code.  Your next move is to check the resistance of the injector, plug and harness.  You can get to it from the PCM or a breakout harness connector.  Check the resistance while moving the harness and tapping the injector lightly with something metallic.  If that checks out OK, then you might want to find someone that knows TDIs before you toss a PCM at it.  All kinds of goofy stuff happens on these cars, like replacing the MAF and the needle lift code disappearing.  

If you plan to keep the car, join tdiclub.com.  Good group of folks there and there is NO END to the technical info available there.

Joe

[lmorris]

53 minutes ago, JoeR said:

If you plan to keep the car, join tdiclub.com.  Good group of folks there and there is NO END to the technical info available there.

Joe

I have visited the site a few times and agree, the information is abundant. I am astounded by all the crazy fixes for seemingly unrelated concerns. 

I haven't load tested from the ECU yet as Prodemand seems to be wrong on some of the wiring. IE, it shows the horn button on the wiper arm and not the steering wheel.  

[JoeR]

5 hours ago, lmorris said:

I have visited the site a few times and agree, the information is abundant. I am astounded by all the crazy fixes for seemingly unrelated concerns. 

I haven't load tested from the ECU yet as Prodemand seems to be wrong on some of the wiring. IE, it shows the horn button on the wiper arm and not the steering wheel.  

LOL to the crazy fixes.   As a tech you can usually sniff out the things that are totally coincidental, and unrelated to the problem, but with that needle lift sensor there's no shortage of reported unrelated fixes.   

[lmorris]

So, if I unplugged the MAF sensor and rechecked codes, would the P1247 go away if it was the cause?

I must add that Prodemand was absolutely no help, both the 98 and 99 wiring diagrams for the ECU were wrong. Had to check we each pin till I found the right one. Turns out one wire is a shared VREF with 6 other sensors. Wiring is good. I wonder if one of the other sensors is messing with the signal.