No boost - multiple short to ground dtc's

[zortmo]

2001 TDI ALH manual

Anybody seen this before? I cleaned the ECU connectors with deoxit and the boost came back for a few days then stopped working.

Trouble codes:
P1441 - EGR vacuum regulator solenoid valve Open circuit/short circuit to ground
Intermittent
P1619 - Glow Plug Relay Open circuit/short circuit to ground
Intermittent
P1549 - Wastegate bypass regulator valve Open circuit/short circuit to ground
Intermittent
P1252 - Injection start valve Open circuit/short circuit to ground
Intermittent
P3105 - Intake manifold flap change-over valve Open circuit/short circuit to ground
static

 

[wonneber]

Every time I see multiple codes and Intermittent I think bad ground and/or frayed/broken wires.
I do a voltage drop test from the battery negative post to the grounds of the circuits listed.
I would not want to see more then a few tenths of a volt drop.
The wiring diagram for the car helps.

 

[BobnOH]

Well that's cause you're smart. These cars are getting old and the small signal wires used are well, really small.
I'm a little concerned about the code read being 100% accurate. Try the Ross Tech wiki to see what common issues are listed. If you get the chance re-scan with a vag tool like vag-com, VCDS. Those codes are probably fairly accurate, just can't be sure.

 

[Rembrant]

This guy had a whole pile of codes the other day, and it turned out to be a blown fuse.

http://forums.tdiclub.com/showthread.php?t=478530

 

[Nevada_TDI]

I am currently having some of the same error messages the OP is having. I have been through this before and I had a wire or two with frayed insulation; I am also having lack of boost issues. I don't remember what value fuse #34 should be, as I don't know if I replaced with an identical amperage fuse or not. Will someone please tell me the proper amperage for the #34 fuse? Thank you in advance.

 

[zortmo]

Bentley shows #34 as 10 amp. May I ask where you see frayed wires?

Wonneber thanks for the suggestion for voltage drop test. Will do.

I believe the scan results to be true as I have Vagcom and OBDEleven.

#34 fuse is good and I cleaned #608 ground point for ecu per bentley.

 

[zortmo]

wonneber, please confirm I did the voltage drop test correctly. I unplugged N18, N75 and N239, turned the key-on and measured between battery negative and both sides of connector. Fuse #34 side of connector (yel/blk) was 12v on all. N18 and N75 both showed around 3.25v on computer side of connector. N239 showed >.1v

I also did a key-on voltage drop of pins 4 and 5 on the ECU (grounds I think) and they both showed a little over .1v

As I said before the ground to chassis right next to ECU shows .1v

I unplugged all the components on this circuit (I think) thinking one of the components might be shorted to ground. No change on voltage drop measurements.

I looked for possible bad places in the cabling but it all looks protected and no kinks.

 

[wonneber]

For the voltage drop test you leave everything plugged in.
A resistance test you unplug the device to test it.
A little over .1v is good.

The N75 3.25 could be OK, its a pulsed device and I think that would need a duty cycle or frequency test. (no info for TDI with this)
The 2 should be OK.

A quick look at the diagram, these all might ground through the ECU, but the voltages indicate they are good.

Did you test for AC in the charging system?
Car running with a few accessories measure for AC voltage.
Could indicate a bad diode in the alternator.

I'm wondering if resetting everything helps.
Disconnect both battery terminals and hold them together for a few minutes.
You might loose the radio settings, and will loose the trip mileage.

Running out of ideas.

 

[zortmo]

So are you sticking a pin through the wire insulation to measure voltage drop with component plugged in?

After reset and putting everything together the boost is back. I cleared dtc's and now only egr limit exceeded and glow plug heater circuit errors. All the short to ground faults are gone. It's done this before. Not the fix I was hoping for.

I show 30 volts AC across the battery terminals with engine running. How much is too much?

Thanks for the help friend.

 

[BobnOH]

That's how it's done. Either that or you put a tee to the connecter, difficult for a multiple wire connect.
Cars are DC not AC.

 

[wonneber]

So are you sticking a pin through the wire insulation to measure voltage drop with component plugged in?
After reset and putting everything together the boost is back. I cleared dtc's and now only egr limit exceeded and glow plug heater circuit errors. All the short to ground faults are gone. It's done this before. Not the fix I was hoping for.
I show 30 volts AC across the battery terminals with engine running. How much is too much?
Thanks for the help friend.

30 volts AC is way to high.
I would have it checked for bad (shorted) diodes.
Can you unplug the alternator wires (not the heavy one), clear the codes and scan it again? Maybe go for a quick ride.
With the alternator wires unplugged check for the 30 volts again.

 

[flee]

Please don't unplug the alternator with the engine running.
What is the DC voltage at the battery?
Have you checked and cleaned the ground connections?

 

[wonneber]

My bad.
Unplug the alternator plug, not the heavy power cable.
Then start it and do the above (post 11)
The alternator will not turn on and there should be no AC reading or charging.

 

[zortmo]

Wonneber,

I looked at the Bentley. The two wire connector on the voltage regulator, one wire (L) goes to the instrument light, the other goes to ecu (DFM). If and when the condition comes back I will test by unplugging that connector, clear dtc's and see if I see any change. I may also hook my oscilloscope to the DFM connector checking for AC noise. If part of the rectifier bridge is bad there may be a lot of noise there causing problems at ecu.

At present I'm enjoying having boost.

 

[wonneber]

Glad its working again, lets hope it lasts.

 

[firehawk618]

I haven't looked at a schematic but I bet you they all share a common reference wire or common ground wire.

If they are all indeed on the same circuit which is very likely.

 

[zortmo]

Firehawk, here's what I see on the schematic;

Glow plug relay (switching side) power comes from hot side of fuse #34
N18, N75, N108 and N239 all get power from the fused side of fuse #34
So all 5 dtc's have fuse #34 in common. That fuse seems fine. I'll double check under load.

N18, N75, N108 and N239 all get their ground signal from ecu. They appear to all be pull down signals and the ground is right next to the ecu, clean and tight.

Glow plug relay (J52) gets it's switching signal from the ecu but I think it might be pull up rather than pull down like the others. This relay seems to be separate from the other dtc's yet its always present when they are.