Glow Plugs or GP Relay

This is a "partial" copy and paste from the Glow Plugs 101 ***Ver.201*** by Wingnut.

Wingnut said:

The glow plug codes are a popular code to be thrown on our cars. Several versions of the DTC are

16764 / P0380 code (Glow plug/heater circuit electrical fault (Q6))
17055 / P0671 code (Cylinder 1 Glow plug circuit (Q10))
17056 / P0672 code (Cylinder 2 Glow plug circuit (Q11))
17057 / P0673 code (Cylinder 3 Glow plug circuit (Q12))
17058 / P0674 code (Cylinder 4 Glow plug circuit (Q13))

The first code is for 2001 and older cars. They have a 2 wire glow plug harness, so just throw a generic code for the glow plugs.

The other codes are just examples of codes you might find on a 2002 or newer car. They have a 4 wire harness, so the ECM can specify the problem plug.But the trouble shooting procedure is the same for all three codes.

Click to expand...

..........

I'm getting 16764 / P0380 code

So, the car I am working on is a 2001 with the 2-wire harness which was replaced sometime prior to June 2013 when the guy purchased it (I did a TB job on it that month). The harness looks just fine... no cracking, the splice looks crimped really nice and had tape over it.

I pulled the harness and plugged in a known good GP....... grounded! Then, I cycled the GPs several times ........ no get hot, as in no smoke either.

So, is this a GP Relay issue? If so, where is that sucker located?

Or, is that "splice" the issue?

If you use VCDS to do an output test on the engine computer, you should be able to get the glow plug relay cycling. It's located in the dash relay panel, near the driver's left knee.

I'd venture that the relay could be bad too. Hmm, isn't there a fuse too? I've never had to mess with it on my car so I don't know if there's a fuse / where it would be located. The late A3 cars had their GP fuse mounted right by the relay.

-J

On the 2001 it's the 180 relay up on the fuse panel under the dash. It was moved out under the cowl in succeeding years.
http://forums.tdiclub.com/showthread.php?t=473687
Oilhammer in post #18 tells what's what on the relay.

Yeah, I believe the MK4 02s and 03s have the GP Relay out under the cowl ... I done checked there with no luck.

Anyway, I believe the problem is either the Relay or the fuse as Compu_85 suggested.

EDIT: Well, duh! I should have known where that fuse is located. It's on the battery! I went though most of these wiring circuits with my conversion project, but it was with an 02 engine.

And, TDijarhead, thanks for the link. Oilhammer's post jogged my memory!

I'll look closer tomorrow.

.................

One other crazy question, would a malfunctioning Thermo -T at the Fuel Filter in combination with a very dirty fuel filter cause excessive back pressure in the IP?

The IP seems to be leaking fuel everywhere possible when the engine is idling. Seems the shaft seal is okay because the car started just fine after sitting for more than two days, even with no GP operation. From the looks of the outside of the Fuel Filter, it appears to be very, very old.

Well, thanks for the replies..... this car belongs to a long time friend.

Well, I learned something reading thru this. I knew where the GP relay was on my 2003 because I removed it and mounted it into the 2003 gas to TDi conversion car project. But, I didn't know the GP relay in my 2001 was under the dash.
As always good info.
Don't know about that leaking IP/fuel filter/"T" fitting theory. Maybe, who knows.

Okay, problem still not solved... (New Battery with 12.68 volts)

I did go to the Thread in the link above that TDijarhead provided. I read Oilhammer's explanation at Post #18 of J52 (Glow Plug Relay 180) and studied the wiring schematics... I understand it. However, #9 is not fused. That circuit comes off a hot circuit(s) before Fuse 232 (it is an 86 circuit, meaning hot with ignition ON). So, nothing there is fused that provides operating current to Relay 180 (it's direct non-fused current from the power supply [109]). I am using a Bentley manual that covers the 01 Jetta. My NB Bentley has an error in printing. They double printed two schematics and left out two... but, what's there is identical to the schematics for the Jetta.

Anyway, this is what I've confirmed thus far:

1. Fuse in the panel at top of the battery is good.
2. Confirmed that the circuit from the Fuse at top of the battery to Relay 180 is hot (the one for the big spade on the relay).
3. Confirmed that the two circuits going out to the GP harness have continuity (the two spades half the size of the big one).
4. Changed Relay 180 with a known functioning relay.

The Relay 109 is Grey... (no other DTC than the P0380, thus that relay should be okay).

Due to several relays clicking, it's really difficult to discern whether or not the 180 is functioning when I turn ON the iginition... don't think so.

I unplugged the Coolant Temp Sensor ..... no help!

So, does this mean I have to drop the fuse/relay panel and start chasing those other circuits.

The circuits of Relay 180 are rather simple as Oilhammer's explanation provided.

1. Power "IN" for the GPs (one circuit)
2. Power "OUT" via one circuit to 2 GPs.
3. Power "OUT" via one circuit to 2 GPs
4. Power "IN" to operate the coil and related solid state circuitry.
5. Ground for the coil and related solid state circuitry
6. Circuit to/from the ECU
7. Circuit to/from the ECU

Scratching my head...

Edit: The numbers above are just the order I put the circuits in..... nothing from the schematics.

So if you have power to that big middle spade on the fuse panel at the 180, and it's not making it to the other two spades that feed the glow plug wires. That would seem to be a control issue either a bad 180 or is there any possibility as in my case that the ecu was swapped out? Perhaps for some other issue?

Well, I did install a known good 180 and got the same results.

Nope, no ECU change out. This Jetta belongs to a friend of mine. He purchased it in May of 2013. He's the 2nd owner. The seller told him the TB had never been changed. It had 149k miles on. So, I changed the TB for him in June, 2013. The vehicle now has 195k miles on it.

As I understand the CEL come on about two months ago. Local parts stores did a scan and got the DTC for GPs. I got the same code with my VCDS... no other codes.

He did have a starter installed about a year ago.

The typical left door pull bar is broke but the window and door controls all work. I do have a new assembly to install.

Just to clarify, you have NO voltage showing up at the GP harness ends?

The glow plug feed goes into another plug in the duct under/behind the air filter box. On mine it's 2 brown wires. I believe you can pop off the duct cover with just the box out. Might be a good place to check for volts.

BobnOH

You may be onto something..

I noticed yesterday that the cover over the relays to the left of the wiring plenum at the fire-wall wasn't latched properly. Someone may have been in there looking around. Also, it was obvious the air filter box had been jacked with. I'm not sure if that was due to changing out a battery or air filter or someone looking for the GP issue.

Well, I've just now (4:15 pm) found time to get back and do some more testing. After this evening/night, it will be Friday before I can get back to it.

Thanks for all the suggestions/comments to this point.

I tried a different Relay 180 ........ same DTC. Nothing changed. (3 Relays counting the OE unit)

Note: Read update at bottom

Okay, below is what I have confirmed (some of it twice as stated previously)..

1. Power "IN" for the GPs (one circuit) (Big spade, 30 circuit always hot........ checks good)
2. Power "OUT" via one circuit to GPs 1 & 2. (Checks good with Ohm meter)
3. Power "OUT" via one circuit to GPs 3 & 4 (Checks good with Ohm meter)
4. Power "IN" to operate the coil and related solid state circuitry. (This is an 87 circuit [switched power via Relay 109 <<< works fine, 12 volts])
5. Ground for the coil and related solid state circuitry. This is a 31 circuit (constant ground <<< works fine as shown by my Ohm meter)


6. Circuit to/from the ECU (circuit ST) << with ignition ON, this circuit shows 3.06 Volts (never did turn off) (maybe I didn't leave ignition on long enough)
7. Circuit to/from the ECU (circuit D1) << with ignition ON, this circuit shows 11.08 Volts (never did turn off) (maybe I didn't leave ignition on long enough)

(Note: those are my numbers for the circuits. Not from the Bentley.)

So, now it is boiled down to the two ECU circuits and I have no clue how to test them. Does the ECU send a singal to the GP Relay via these two circuits to turn it on........ obviously it does?

Or, is the circuit from the Engine Coolant Temp Sensor bad? I did unplug the CTS with no change in the GP operation.

Other than the Fuse on the battery for the GPs, nothing else in these circuits has a Fuse. The 87 Circuit (#4 above) is always hot with no Fuse from the Relay 109 when ignition is ON. The Schematics in the Bentley are quite simple on these circuits.

I think the bottom line is, something is causing the ECU to not turn on the GPs. Then, when it senses no current drawn, a DTC for P0308 is thrown (GP heater circuit intermittent).

Edit:

Update...

Okay, I checked volts at each individual GP harness connector (used all three 180 Relays).

When I turn the ignition ON, for a split second there is 0.975 Volts ....... then voltage drops to 0.334 and stays there until the ignition is turned off (roughly the same for all four GP connectors). Seems Wingnut mentioned in his Sticky that the voltage hung around 0.300 and really never hand an explanation!

So, I unplugged the brown/black connector in the wiring harness plenum on the firewall and checked voltage there ...... same thing, only slightly lower for some strange reason.

Does the ECU control the amount of voltage?

Do you have a spare ecu 99.5-01?

Yes, I do have a spare..... seems it is a 2000 from a Jetta!

I got it at a junk yard for $10.00 due to being exposed to the weather (someone stripped out the wiring harness and left the ECU). I did install it in my Vanagon for a Test. It did allow the engine to start and then shut-down.... immobilizer! So, it should be good!

AndyBees said:

.......................................................................................When I turn the ignition ON, for a split second there is 0.975 Volts ....... then voltage drops to 0.334 and stays there until the ignition is turned off (roughly the same for all four GP connectors). Seems Wingnut mentioned in his Sticky that the voltage hung around 0.300 and really never hand an explanation!

So, I unplugged the brown/black connector in the wiring harness plenum on the firewall and checked voltage there ...... same thing, only slightly lower for some strange reason.

Does the ECU control the amount of voltage?

Click to expand...

Never having been this far into that system, I'll try...
I don't think it's that complicated. Ignition on I would expect to see 12v (7v on some of the newer A4s). But 1 volt seems the same as 0 in this application.
The ECU does coordinate with the other sensors, it also times the "on" period, but I don't think it varies the voltage, maybe 2 stages.
With the engine cold, check the various temperature readings with the VCDS device, maybe something is telling it it's warm.

Well, I just now got back to this contraption..

VCDS shows all temps to be in the normal range at engine fire-up! Coolant, air temp at charge sensor, fuel temp, etc. And, a couple of days ago I unplugged the engine CTS which never changed anything.

So, using 3 different 180 Relays and 2 different 109 Relays, there hasn't been any change in the voltage.

Deleting the DTC doesn't change anything either... no other codes in any of the systems that my VCDS will scan.

Surely someone has been down this road previously!

Andy, if your head is spinning then mine has become detached!

I'm wondering what kind of codes you would see if you clear the codes and unplug the GP relay.

UhOh said:

Andy, if your head is spinning then mine has become detached!

I'm wondering what kind of codes you would see if you clear the codes and unplug the GP relay.

Click to expand...

Codes with the GP relay disconnected may indeed be interesting. Puzzling, but electronics and wire chasing quickly boggle my mind.

I'm not much at chasing down wiring problems. Although I have managed to overcome a few, mostly with a huge helping of just plain old luck.

If you've got a spare ecu I think I'd try that next, only because chasing wiring problems as I said is just not my thing. I've not had to change out an ecu on a golf or Jetta but I know a beetle can be done in less than 15 min.

The ECU is under the cowl about dead center of the vehicle below the windshield. I do have the cowl off (I unplugged the ECU and re-plugged, nothing changed).

No other codes show when the GP Relay is unplugged.

Actually, I have three ECUs. One is the junk yard pick from a 99.5 or 00. The other two are in 01 Jettas that I've picked up here and there.

One of the Jettas has a bad auto tranny but the engine will start and run. So, tomorrow, I'll install a battery to check function of these three 180 Relays.

As a matter of desperation and curiosity, I broke open one of the 180s. It looks nice and clean inside. There is a single set of contact points that connect the Big Spade to the two smaller spades that go out to the GPs. Using a mirror to observe, I switched on the ignition numerous times. The contact points never moved. There is continuity on the coil. There is a circuit off each of the two Spades. They are connected to the solid state circuit board. That may be how the ECU monitors the GP circuit.

Anyway, the rest is solid state and beyond my pay grade.

I do have pics that I'll post as soon as I get them into the gallery.

Okay, FWIW, here are a few photos of the Glow Plug Relay 180.

Narrative is a the top of each photo.

Below, is a view of the spade end of the Relay

Across the top, 31 ground, 30 big hot spade, ST to ECU
Middle, Glow Plugs 3 & 4 and 1 & 2
Bottom, 86 switched power from Relay 109 circuit and D1 12 volts from the ECU




Below, is another view of the spade end at a side angle..




Below, is a view of the guts ... Notice the contact points are to the left of the yellow dot.



Below, in this view you can see the braided bare wire connects the Big Spade via the contact points to the two smaller spades that go to the GP circuit out front.



And, below, is a view of the Solid State circuit board...

Well, in an effort to confirm the status of the three GP 180 Relays, I got one of the 2001 Jettas running (hadn't been started in almost 3 years).

Anyway, I checked each Relay. Only one of them threw a DTC... it was not the one that come in the car I am working on. Amazingly, the car I got going for Test Purposes has the OE GP harness...... broken up pretty bad but still plugged to each GP.

During the testing, I started the car numerous times with each GP Relay. Only the one would through a DTC.

I forgot to check voltage until after the engine was fully warmed up. So, in checking volts with the hot engine, the meter would only show a little over 0.50 volts for a split second and then drop to a little above 0.20 volts and stay there. So, I guess once the engine is fully warmed up the GPs really don't come on.

So, other than running the circuits on the Test car for comparison, I am at a total loss.

Problem solved ........

Problem solved................................... Wow!

16764 / P0380 code (Glow plug/heater circuit electrical fault (Q6))

As stated by WingNut in the Glow Plugs 101 Sticky:

"The first code is for 2001 and older cars. They have a 2 wire glow plug harness, so just throw a generic code for the glow plugs."

So, here's the deal, I was hung upon the word "circuit" in the DTC explanation. Notice that code also includes the words Glow Plug before the slash (/) ... Duh, that went over the top of my head.

And, the Bentley plainly says the "pre-glow" doesn't take place until below approximately 48F (9c). I've been working in temps above 70f.

But, the Bentley also says that the "after-glow" will take place with a warm engine regardless of temperature. So, the very low voltage I was seeing shortly after the GP Light turned off was what also contributed to me being stumped.

Anyway, a new set of GPs solved the problem.

I noticed that generic code thing also when I was chasing my problem. The four wire system allows the ecu to be a little more specific on what the problem is and which plug it is. The 2 wire system is not so helpful. Glad you found it.