Error Code P0674

Hi,

I've had an 03 Jetta TDI now for my second winter. Last winter (1st year) the car struggled to start when it got cold (Wisconsin) and as the winter progressed the problem got worse. I did have all of the usual stuff checked (@ a VW dealer) like the glow plugs, fuel flow, etc...and I was told all is well. I was told the starter needed to be replaced and I did that to no avail.

This year, I got an oil pan heater installed and that helped immensely when I have access to a plug. After sitting all day at work starting it at 5 pm has not been a good experience. In fact, I think I'm destroying the starter. About a week ago now, for the first time since I've owned this vehicle, the engine light came on. It is being reported as a problem with the number four glow plug circuit (PO674).

Here's the weird stuff...since the engine light has come on, the car has been starting like it is a summer day (no problems) with very cold temps, starts right up on the first turn.

I'm not sure I want to attempt to fix this because it now starts without problems.

Does anyone have any thoughts on this?

I would check the glow plugs 101 thread to troubleshoot: http://forums.tdiclub.com/showthread.php?t=79819

Could be that your colant tenp sensor wasn't working causing the glowplugs not to operate correctly. Now that you have the CEL its just turning the plugs on regardless

First thing is the dealership "service" department is usually clueless about TDIs.
Previously when it was cold, how long did the "wait to start"/GP indicator stay on? How long does it stay on now??
The coolant temp sensor data determines how long the ECU keeps the GP on. Generally when its bad it doesn't throw any codes and causes very short GP cycles. If its disconnected, it defaults to maximum cold temp and keeps the GPs on a long time, which helps cold starts, but also does crazy things to injection timing (very advanced).
On your '03 if the code you have for GP #4 is correct, it is actually GP#1 that is affected. For whatever reason they get numbered backwards, so the connector or GP that is throwing the code isn't the right one by way of cylinder numbering.
.02

Thanks for the info. That comment about the VW service guys not having a clue is surprising to me. I thought if anyone knew the VW TDI it would be them :-(. Not being a mechanic I'm wondering who to go to when I have a problem. Do truck stops usually have folks there that understand a diesel and maybe a VW diesel?

Over the last 2 winters the GPs stay on variably. When cold, the first turn on can be as much as 10 seconds. After the first turn on, the time on decreases with each successive turn of the key.

This winter I got smart (or so I thought) and activated the GPs 6 or 7 times prior to turning the engine over. This seemed to help a bit but jsut prior to the engine light coming on it was getting bad. I could sit for 15 minutes trying to turn her over.

Since the code was thrown the car starts like its a hundred degrees out?

You can check the trusted mechanics thread to find a guru near you: http://forums.tdiclub.com/showthread.php?t=130044

That being said you can run through most of the glow plugs 101 thread fairly easily if you want to try and track down the issue by yourself

GPs aren't hard. think of them like easily accessible spark plugs. Pull the harness, check the resistance between the top pin of the plug and the block. Odd one is bad. If they all read OK its a bad harness. make sure you don't break them when you remove them. If they don't want to come out, soak them in PB blaster overnight. Sometimes helps to pull them on a hot engine, but I think they should be installed cold. Use anti-seize on threads when installing.

JasonTDI is Mad-town.

Electrical contact cleaner on all harness plug connections is recommended.
Don't forget the master connection in the plastic tunnel under the air box.

Thanks everyone! I'm going to try to track this down myself. After finishing will I be able to reset the code by removing the battery or will it be maintained through a power cycle?

Hi Sdeck,

Can you tell me what PB is?

PB Blaster is one of several penetrating oils used to loosen rusted/frozen threads. Any auto parts store will have it.

I don't think you can reset the code without a VCDS or a generic OBD 2 reader. Any auto parts store should read them for free, but I'm not sure if they will reset them. It may just go out after a few cycles or it may not. I'm not sure. I just clear them with my reader.

I haven't had a chance to T/S this yet due to subzero temps. I've been watching my fuel usage since I bought the car where I've been getting from 39 to 42 mpg.

Since this code was thrown I'm now getting about 35 mpg. Still starting like a champ in bitterly cold weather.

Is this just really weird behavior or is there an explanation for this?

Winter loss of fuel economy is well known in these engine. Winter fuel is lower BTU content, poor efficiency until it warms up fully, higher electrical load (blower, seat heaters, electric heaters, GPs, defrosters, slower traffic, etc.), and so on…. Lots of discussions about this around here.