How often do ALH computers go bad?

Postmortum

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2002 jetta tdi 2009 tdi wagon
Hello everyone, I have a very big dilemma. I have a 2002 TDI Jetta with around 270k miles on it. The other day I noticed the A/C was blowing hot at idle, checked it out replaced the main cooling fan. That problem solved fans working correctly. The next day I am assuming just coincidence, car goes into limp mode. I pulled the battery cleaned all the connections removed and sanded the ground for the battery cable, the ground next to it, removed and sanded the ground next to the computer, and pulled the computer and sprayed it with contact cleaner.
The next day the car ran fantastic no codes put about 50 miles on it. Day 3 same issue on the way to work. Here are my questions
1. How often do the computers malfunction?
2. can the 109 relay be an issue even though the engine runs and starts every time?
3.Does the check engine light with no flashing glow plug light still mean "normal" limp mode

Here are the codes in limp mode with VCDS
19561 16629 17964 17849 16600 all open or short to ground. I have a hard time believing all this could happen simultaneously overnight. Also the car will kick out of limp mode some time after a few miles of driving at 25mph and back to normal for ? amount of time.
Thanks in advance for any help I drive 80 miles round trip every day to work I can't afford to not have this car running
 

jasonTDI

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Check 109. Should be Gray. Replace anyway, cheap.

Doubt its an ECM issue. Make sure the battery cables are TIGHT. Seen this with bad connections.
 

Vince Waldon

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2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
My personal opinion: the ECU is one of the most bullet-proof parts of the car...rare to see an actual failure that isn't actually something else. :)

Relay 109 is a great place to start, as posted above. Water in the ECU connector itself can cause lots of mischief (did you check both sides of the connector for corrosion?) , as can poor grounds *under* the battery box.
 

IndigoBlueWagon

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Postmortum

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2002 jetta tdi 2009 tdi wagon
Thanks for the fast responses. I have checked for corrosion at the ECM and cleaned it with contact cleaner and blew it out before re assembly. I cleaned all the grounds and leads under the battery tray and by the ECM. I have been trying to read all threads pertaining to this debacle. I have come to the conclusion that a 109 relay will cause a "no start or run" problem, but am still going to pick one up anyway. I am suspecting an ECM because I have 4 solenoids that are "open or short to ground" over night.
Thanks for the links I WILL read everything I can on this. I am trying to get a wiring diagram on this car, I bought the VagCom and have a multimeter and power probe but no idea what pins to check.
 

TornadoRed

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Any limp mode issue on an ALH and the first thing I'd look at would be replacing the vacuum hoses. They are 12+ years old, stiff and prone to air leaks.
 

Postmortum

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2002 jetta tdi 2009 tdi wagon
Vacuum hoses have all been replaced about a year and a half ago maybe two years at most. Do you think a vacuum leak could throw 4 short to ground codes? To me it seems like more of a electrical problem? Maybe I'm going about it the wrong way, I need to test and see what kind of vacuum the car is getting, possibly a bad pump?
Also if the computer is bad, I know the immobilizer is an issue. If I get one from the exact same Jetta it will still need to be done correct?
Thanks again
 

RichJetta

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Vacuum hoses have all been replaced about a year and a half ago maybe two years at most. Do you think a vacuum leak could throw 4 short to ground codes? To me it seems like more of a electrical problem? Maybe I'm going about it the wrong way, I need to test and see what kind of vacuum the car is getting, possibly a bad pump?
Also if the computer is bad, I know the immobilizer is an issue. If I get one from the exact same Jetta it will still need to be done correct?
Thanks again
I would look for a worn wire. if you disturbed the wires maybe something is contacting ground. I removed the electronic actuator on my BEW and the connector eventually shorted to ground. it killed power to n75/n18 and ran like limp mode. to make things worse it would come and go. it turned out that my connector came loose from where i had tied it off and melted on the exhaust.

Richard
 

oilhammer

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outside St Louis, MO
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There are just too many to list....
I've replaced several late (2000+) ALH ECUs for multiple DTC problems before. Not very common, but it can happen. Some output stage or voltage regulator inside them must die.

IIRC, in every case, it was the same faults: for the N239 intake flap solenoid, N18 EGR valve, J52 glow control unit, N75 VNT control solenoid, and N108 cold start injector (inside the pump).
 
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AndyBees

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For what its worth:

When I was doing my conversion project (2002 ALH into a Vanagon), I accidently let a big hot wire drag acoss the outside of the ECU .......... sparks glore! The ECU survived without any problems, in fact, it now has a Malone Stage 1 tune.

You've received lots of good advice from some excellent gurus!
 

Postmortum

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2002 jetta tdi 2009 tdi wagon
Thanks to everyone for the responses, I am going to go over it again tomorrow and look for broke or shorted wires. I am talking to Chris over at Kerma and maybe getting something going on a 5spd conversion and a tune on a possible replacement ECU. I really hope I find a short but I'm no longer holding my breath.
 

oilhammer

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outside St Louis, MO
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There are just too many to list....
You should be able to find a used ECU I would think. I have one from a 2000, but I don't think it will work. However, if you can find out that it can be made to work, you can have it.
 

IndigoBlueWagon

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A MY2000 will work in a 2002 (immo deleted, of course) and vice-versa, but you'll have a glow plug fault because of the different glow plug setup in the two cars.

Go to www.car-part.com and look for one for an '02. I've found a couple there, usually around $100-150. They're easy to ship, so it can be anywhere. Just match your ecu's PN exactly, including the suffix.
 

Joester

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I bought mine from AArod. He had one on-hand so you might try him out if you have any trouble finding one. I'm sure he'll match one to your car, too, and he can do immo deletes so its a one-stop-shop.
 

Postmortum

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2002 jetta tdi 2009 tdi wagon
I love this site, everyone here is so helpful!!! I talked to Chris over at Kerma, they have one that they can send me ready to go in the car. However I really want to verify this before I just throw money at the car. I'm trying to locate a Bentley for my car, Could someone tell me the pin location in the ECU for the wires so I can test for an open circuit? I need,
1. N239
2.N75
3.N109
4.N18
If you can tell me where the wires are at looking at them from the back of the wires as if they were plugged in, I'm pretty sure they are all by each other. Thanks all
 

Alchemist

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'04 ALH Golf
Here is all the information I have at hand now. T121 is the ECU connector, and the pin numbers are on the connector. Pin 1 of the valves connects to the output of relay 109, which from memory, is on fuse 32

N239-2>T121-81
N75-2>T121-62
N109>T121-120
N18-2>T121-61

HTH
 

Postmortum

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2002 jetta tdi 2009 tdi wagon
That is awesome!! I will check it out tonight, verify it and if it is for sure bad I'll order it tomorrow. That is of course if Kerma is open on Saturday. Thanks for the info I will be ordering a service cd this time as well.
 

BobnOH

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central Ohio
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That is one part I would recommend going to a salvage yard. Maybe car-part.com.
You need the one with the exact part no.
 

faul713

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2003 Jetta, 2004 Beetle, 2005 Beetle, 2005 Jetta
I know it's been 4 years but what ended up being the problem?

You got a lot of good help here, can you post the solution so those of us who still have these cars can learn from your experiences? Thank you.
 

jmodge

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http://forums.tdiclub.com/showthread.php?t=491803

Another thread on ecu issues. If you read the first post it will explain two N75 tests I performed. one engine running, one engine off. If you read further, there is some ecu compatabilaty numbers toward the end
 

jmodge

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Suffix 012bd and 012cp I found to be compatible, early alh glow plug systems. 012gn was in my '03, and is the later alh glow plug system. I heard they switched over during the '02 model year, check your suffix.

Put a want to buy ad in and you will find something. Found there was plenty to be had for $50 if that is your issue
 

jmodge

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2001 alh Jetta, RC2 5speed daily commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/502's backroad cruiser
Hmmm, Just noticed I am four years late With my advice
 

jmodge

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Mongler98

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Mar 23, 2011
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COLORADO (SE of Denver)
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98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Only time an ECU goes bad is from 1 of 3 things, really only 2
Flooding damage causing a short to the ECU bypassing the fuse, an electrical surge (extremely rare) or extreem heat from fire or over voltageing ( again bypassing the fuse)
Or the owner pulling it apart and shocking it or damaging it during the line replacment or map replacment mod. Or chip tuning
There is a chance of it going bad at random but all the threads here about it always have that rom code error that is not related to the boost line going bad and actually is a rom error.
Never heard of a bad ECU having a limp mode issue. It's either go or no go
 

GEFP

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I'm going to subscribe to this thread. I have a 2001 with limp mode issues. Thanks for all the good info here.
 

jmodge

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2001 alh Jetta, RC2 5speed daily commuter and 2000 alh Jetta 5spd swap, 2" lift, hitch, stage 3 TDtuning w/502's backroad cruiser
When mine went bad, when it sat for close to a week, it would work fine for just under 15 miles. Boost would completely leave and would not come back with a key cycle. Had to sit for a while, but would never make it 15 miles without it happening again
 
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