2004 jetta bew whole whack of electrical codes

[Rockmonton]

Picked up a new car after blowing up my f150, haven't had a VW in years so please bare with me. Feels like car is in limp mode, or else just really gutless. Can't hear turbo spooling.


Unfortunately I don't know anyone with vagcom for a few hundred km around, but the generic obd2 picks up the following

P0670 glow plug module 1 malfunction
P2102 SAE: throttle actuator control motor circuit low
P0245 solenoid valve a for boost pressure control (N95) short to ground
P1027 intake manifold tuning valve control circuit short to ground
P2426 EGR cooling valve control circuit low
P0726 RPM signal from ECU implausible

Tach works, so 0726 is a bit odd.



All of these Individually have their own common fixes, but given everything that pops up I'm wondering if there isn't a larger electrical issue I should be looking for? Any ideas where to start? It's -25 out so I'd like to avoid as much time outdoors as possible

 

[Tdijarhead]

Check your battery with a multimeter what does it read with the car just sitting in your driveway? What does it read running? Check the fuse block on top of the battery for melted plastic and wires. There are also several grounds underneath the battery tray. You will need to pull the battery and then the battery tray to get to them. Clean them up, make them shiny.

 

[oilhammer]

In addition to checking all the fuses and grounds, I'd check the engine bay wire harnesses for any damage, especially from mice. Particularly at the subharness up on the firewall (there is a big connector right there). That goes to some of the stuff you have listed there. Without a proper scan tool that speaks fluent Volkswagen, though, I am afraid you may be chasing ghosts.

 

[Rockmonton]

It's -25 today, I can't get it going for the life of me. I almost dragged out the ether before having a look to see how bad it is first.... now I see to try WD40... but I can't figure out a nice spot to inject it without pulling screws. Any quick answers before I go digging?

Battery voltage sitting is 12.68. It can crank for minutes, but I threw a charger on after to be safe

 

[oilhammer]

Well first, if you have a DTC for a glow control module (assuming the generic scan tool is to be trusted), the engine is NOT going to start at that temp. There is no preglow happening. The glow controller is not working, not responding to the ECU, or something.

I would again urge you to look where I told you to look, and perhaps look in the cowl area (you'll need to remove the wiper arms for access) to see if the glow control module (a relay, essentially, which lives in the cowl) has a bunch of mice chewed wires. Those relays rarely fail, so I would be inclined to do a visual check first.

 

[Rockmonton]

Alright, rough pass visually all harnesses look good, free of oil, no obvious cracks where loom ends are.
have power through fuses, no power at glow plug harness (obviously). I’ll be pulling battery and checking under tray when my fingers aren’t numb.

is there a good exploded diagram of harness locations/wiring diagrams? I’ve been googling and searching forums for about an hour and coming up short. Aside from that, can someone recommend a good service manual instead?

 

[BobnOH]

Were you able to clear the codes? I mean those could be stored from the life of the car.

 

[Rockmonton]

I cleared them and went for a drive last night and they all came back. Definitely in limp mode. 0-100kph in about 44s.

Managed to modify a 2 jaw puller into getting the wipers off. After working with a torch/wd40/wiggle for hours.

Then it got dark out, so on hold until tomorrow.

Car did start at about -10, albeit expectedly rough and with a good amount of cranking.

 

[Tdijarhead]

As oilhammer pointed out those relays usually don’t go bad. If the wiring is ok and you’re still not getting power check the fuse block on top of the battery they are prone to overheating and melting and one of those fuses supplies power to the glow plug system, I forget which one. If everything checks out then my next step would be replacing the relay.

 

[Rockmonton]

The fuse box on top the battery is super shiny and nice -- probably replaced recently.

Just making a spudger to get the cowl clips off and then it'll be back to brave the cold.

Worst case scenario, if I manually actuate the relay (splicing into the control pin) ... assuming the relay works, would that cause any damage? What actually drops the voltage down to the 5-7v the glowplugs see?

 

[Rockmonton]

Okay, I've got the module out, I have power to pin 30, continuity from all the G1-G4 to glow plug harness.

Is there a way to easily test the DI and ST from the ecu? I'm imagining I'd need an oscilloscope to see the PWM in it.

 

[Rockmonton]

with a volt meter across DI and ST pins I get ~5,5v
Pin 31 on the harness goes to chassis ground and battery ground as it should
Pin 87 is normally a relay output, but since G1-G4 go out to the plugs, i'm assuming something is different with this one.
I get about 170 ohms between 31 and 87.

 

[Rockmonton]

Decided to open up the module, a lot of kit in here. Solder joints look a bit cold, so going to reflow them. Test tomorrow will be to see if the gate on the MOSFETs get a voltage from the ECU or not, and whether the FETs actually work. If they work and I can't figure it out I'll just make a voltage divider circuit that outputs 7v on the drain and make a manual activation circuit until my VCDS cable gets here.

More to follow

 

[Rockmonton]

alright, cracked open that relay,

I get no voltage on the gate-zero reference. So that means either driver circuitry in module or the ECU.
Given other symptoms i'm thinking it's more towards the ECU side of things.
Mosfets do test okay though, so I can make a quick fix for the time being.

Still looking for a wiring diagram. Does anyone know where the ECU grounds are in relation to chassis/engine/sensors? I'd like to make sure those aren't floating. I can see where they are in one of the ECU pinouts, but to dissect harness would be a whole other ball of wax.

 

[Rockmonton]

Aaaaaaaand I'm a dumbass. Decided to measure fuses rather than visually inspect.... fuse 34 was open. Fixed, now I'm down to v an accelerator pedal response code