1998 jetta P0605


New member
Jan 25, 2023
1998 jetta
hello all,
so I picked up a couple 98 jetta's. one had a check engine light when I got it, I have a vagcom, reading the codes, it was a glow plug code, I replaced glow plugs and harness, code is gone, but a new code appeared after maybe 10 miles of driving. P0605, which is a ROM error in the ecm. when driving, on accel from dead stop, its sluggish in first gear up until about 1500rpm, then has plenty of power and accels fine through rest of gears. this is my first ahu tdi, so I am no expert on them. I also discovered a connector on the passenger side with the wires broken from the connector and touching each other, ??possibly intake manifold temp sensor??, could the wires touching have shorted something in the ecm? what should my next move be to figure out my issue?

Steve Addy

Top Post Dawg
Aug 7, 2002
97 Mk3
Have you gone through and conducted all the maintenance that's probably not been done over the years? Air / fuel filter etc etc? I wouldn't run it all that long until you get the timing belt done, it's never safe when you don't know when that was last done. Five years or 60k miles, which ever comes first.

You didn't mention how many miles are on these either...that would be good to know.

You'd have to figure out exactly what sensor has the bad connection in order to know whether it affects the ECU. A photo of the sensor showing where it's located would help.



Veteran Member
Apr 14, 2010
New Mexico
1998 Jetta TDI, 210k miles
I also discovered a connector on the passenger side with the wires broken from the connector and touching each other, ??
I would post some pictures if you can, would be good to see the condition of the car, miles etc...The intake air temperature sensor should be in the middle of the engine bay on the hose leading to your intake manifold. It's unlikely the problem, but it wouldn't hurt to clean your sensors. What you are describing sounds more like the N75 (which probably needs replacement) or the MAF sensor plug which can get unplugged even it looks like its plugged in (although this will probably give you a CEL)

The MAF sensor can be problematic and might need cleaning, which is likely if the air filter is dirty. This alone can cause limp mode in my experience. Get some sensor cleaner or MAF cleaner spray, open up your air intake and spray the sensor off.

N75: https://www.idparts.com/ahu-n75-valve-028906283f-721895550-p-451.html

But yes, replace your ECU hose: https://www.myturbodiesel.com/d2/1000q/a3b4/ecu-hose-chip-tdi-65535.htm

And buy a new relay 109: https://www.idparts.com/relay-109-a4b4a3-1j0906381a-1008300003-p-350.html

Otherwise, the usual stuff, oil change, air filter, timing belt, battery. When I got my Jetta the vacuum hose to ECU did indeed need to be replaced, in fact it would be a good idea to replace ALL the vacuum lines and fuel return lines between the injectors.

common how tos:

new owner checklist:
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