Glow plugs issues again and again 2005 Jetta TDI

I have been having the glow plugs issue with my 2005 Jetta TDI for the last 2 years that I am currently at a point to make decision to give up (sell/trade-in the car and get away from diesel) or keep fixing it. The story is a bit long so I appreciate you bear with me.
Background: I live in Toronto Canada and the winter is harsh here. The car is 2005 Jetta TDI currently having about 230K km on it. I believe the engine is BEW type. I bought it original and first owner back in 2004.

In 2009, a service bulletin came out to suggest to change the ceramic 7v glow plugs to the steel-tip 5v and do the ECU refresh. So I did and everything is fine. The new glow plugs have part number N10591607.
I heard there was another campaign later year to change it back to 7v ceramic-tip but steel housing ones. However I never received the letter to suggest me to do so and I didn't have any troubles to start in the cold winter until 2 years ago.

2 years ago winter I started to experience difficulties to start when the temperature was below -10C. The car started eventually after I cycled glow plugs 4-5 times and 10-20 seconds each time. It ran rough for the first 5-10 minutes and then everything was normal. Intermittently the MIL amber light went on solidly and it went off a few days later.
Since last winter the check engine light was on and stayed on there forever. I got the code scanned, it's P0673 and P0674. So I assumed it's glow plugs #3 and #4 faulty. Last week I took the bite by taking the car to the shop and dealership scanned the code again and also ohm-meter tested to confirm it's indeed PG #3 and 4 faulty with high resistance reading. So I let them change ALL 4 PG with the same part numbers from Bosch, and reset the check-engine light.
And guess what, one week later the MIL light went on and stayed on again. So I OBD scanned it again, no surprising same error code indicating faulty PG #3 and 4.

Couple of things I want to mention is that the car never has trouble to start in summer. Even in winter as long as it's started it ran very well after a few minutes. I never felt any symptoms such as losing power, etc.
Also the coolant light intermittently went on and off when the outside temperature below 10C or so. But coolant level is always fine and engine warmed up normally to the middle of the gauge. So I never paid too much attention to that.

I am at a dilemma now. Should I leave it as it is and test my lucks in winter or there is something else I can look up? My next guess is it's wiring harness and/or relay? Not a handy-man like me is afraid to do that such a job myself, and absolutely I am not taking the car back to the same dealership anymore.

Any advice is highly appreciated. Thank you.

Well first, I would want to get the newer software, and switch to the newest 7v NGK plugs, regardless. I'd have a tuner do it, since they will likely do it properly and for less headache. But the dealer *should* be able to do this.

Next, the glow system is pretty simple. There are really only a handful of components. The control unit, the harness, and the plugs.

The plugs are easy to check. They are going to be good or bad, like a light bulb. Ohm testing is quick and easy. If they check good, then the fault is either in the harness (common) or the control unit (less common, but there is an updated version of this for the latest go around with plug updates).

If the same plugs are bad AGAIN, there is a chance that the control unit is sticking ON, and burning the plugs up.

If the TIPS of the plugs are eroded and burnt away, you have some other issue like a leaking injector or... But that is pretty unlikely if the engine otherwise runs and sounds normal.

Right now, you are only giving us part of the story, because that is all you have to give. You have not had any actual diagnosis done this time. The DTCs may be the same, but the cause may be different.

There are lots of TDI folks in Ontario.

oilhammer said:

Well first, I would want to get the newer software, and switch to the newest 7v NGK plugs, regardless. I'd have a tuner do it, since they will likely do it properly and for less headache. But the dealer *should* be able to do this.

Next, the glow system is pretty simple. There are really only a handful of components. The control unit, the harness, and the plugs.

The plugs are easy to check. They are going to be good or bad, like a light bulb. Ohm testing is quick and easy. If they check good, then the fault is either in the harness (common) or the control unit (less common, but there is an updated version of this for the latest go around with plug updates).

If the same plugs are bad AGAIN, there is a chance that the control unit is sticking ON, and burning the plugs up.

If the TIPS of the plugs are eroded and burnt away, you have some other issue like a leaking injector or... But that is pretty unlikely if the engine otherwise runs and sounds normal.

Right now, you are only giving us part of the story, because that is all you have to give. You have not had any actual diagnosis done this time. The DTCs may be the same, but the cause may be different.

There are lots of TDI folks in Ontario.

Click to expand...

Thanks for the info.
Dealer refused to refresh any software to the ecu and they would just stick with what manufacturer stated. That's why they changed to the same 5v steel plugs.

Let's say if it's control unit and/or wire harness and/or relay issue, how difficult is it to do it myself considering so far I only changed engine oil/filters/, fuel filters myself. Any trusted shops and tdi guys you can recommend in the York region area?

ok, something new here. I just scanned with ODB II again. This time it gave me P0674 and P0128.
so it indicates GP# 4 faulty and the coolant temperature below operating range.

I have known the coolant sensor problem on this car for many years. The coolant temp gauge flashes when the outside temperature is below 10C. Now it's 20C there and the coolant temp gauge is off but the check-engine error code gives me P0128. I am positive the coolant level is normal.

My questions will be:
-what P0128's cause could be? a bad coolant temp sensor or a bad thermostat or both?
-which one causes which one under this weather (20+c here)? the bad GP causes engine temp too low?

Sounds like the coolant temperature sensor is flakey. The updated sensor should be green. There are how-to's here if you care to search.

Regardless of your coolant temp sensor, you can send your ECU to kerma to get the update and the new plugs. I recently did it, it's about $325 for the reflash, new plugs, and new controller.

Thanks all for the reply, and here is another update.
Dealer wanted to take another look at the car by "investigating" what it exactly goes wrong and charge me $130 for diagnosis only. I said no. I just spent $600 there to change all 4 plugs and 1 week later one blown out again and now you charge me $130 for just looking at it?
I will try my luck and ride it out through the winter with 3 working plugs and a bad coolant temp sensor, and sell it next year.

Hopefully there are other dealers in your area. $600 to just refresh 4 glow plugs seems high.
Hate to see you sell the car for what should be a minor issue. Apparently the dealer should have installed 7v NGK plugs with the proper software.

The ECU reflash to match the different voltage plugs was a VW-specified change, so I can't imagine why the dealer would refuse what was basically their own TSB.

Rob Mayercik said:

The ECU reflash to match the different voltage plugs was a VW-specified change, so I can't imagine why the dealer would refuse what was basically their own TSB.

Click to expand...

I tried to talk them through show them the list of bulletin. But the guy over there was sticking his story: I hooked up your car to a computer that connecting to a system that in turn tell me this is the type of plugs we should use, and no ECU refresh.

So I settled with 5v plugs hoping it would be the same.
However to be fair, regardless 5v or 7v plugs to be used, the #4 plug burnt out should be totally unrelated. It must be something else, I guess, wiring harness and/or relay. No?

Anyhow, just hope I can survive the harsh winter here with 3 plugs.

I thought the lake kept it from getting stupid cold up there.
I'd want to know for sure if it has the correct software and plugs installed. Doesn't the VCDS device show the software version on the ECU? idk