Help with CEL: Glow Plug Circuit Malfunction

Received CEL after cold start. VAG-COM reports:
1 fault found:
16764 – Glow plug/heater (Q6) circuit malfunction
P0380 – 35-10 - - - intermittent

TDI details: 2000 Jetta w/auto – completely stock @ 55K miles - first time TDI owner - purchased back in May.

Details: This morning was the first 30°F cold start since my purchase, and therefore the first time noticing glow plug light on for more than a second (in this case ~3 seconds). Car starts normally. CEL appears about 5 seconds later. No drivability problems. Cleared DTC on lunch hour, no more CEL (for now).

Here’s what Bentley reports:
16764 P0380 Glow plug monitoring, No display
• Glow Plug Relay -J52- faulty
• Glow plug faulty
• Different glow plugs installed

I haven’t found any posts on the DTCs, but read lots on Relay 109. Also noticed Bentley interprets “intermittent” as possible loose connection. Will apply grain of salt to verbiage between VAG-COM, VAG-1551 and Bentley CD.

Guess I’ll be probing the glow circuits with a multi-meter this weekend.

QUESTIONS:
Anyone familiar with this fault and/or able to decipher Q6, 35-10?
Any recommendations on testing glow plugs (resistance range / operating current range / etc.)?
Other suggestions?

Forum member Wingnut has a couple of relevant links in his signature. A search for his recent posts will show the links. Plenty of useful non-glowplug info there as well...

Thanks. I didn't think to search the How-To's. Found Wingnut's two posts. Thanks for the direction.

Moderator, please drop the post.

Howdy,

I had an identical problem. It turned out to be the harness since I could make the problem go away temporarily by disconnecting and reconnecting the harness.

It happened about 3 separate times so I tried spraying electronic contact cleaner into the sockets that connected to the plugs.

That worked for about a month. Then the problem was back.

The final fix is to replace the harness. If you decide to do that you're replacing the bad harness with a good "for now" harness.....The problem will probably be back. Those plugs draw around 25 A and the sockets aren't really tight enough to maintain a low resistance connection indefinitely. My plugs measured out at about 0.55 ohm with a FLUKE 189 multi meter

It only takes a small rise in circuit resistance for the ECU to detect the drop in current and report a problem.



I went in a different direction. I have owned VW diesels for quite some time. The older diesels had glow plugs that had threads on the connection and used nuts and washers to secure crimp-on tabs.

I removed the glow plugs and carefully threaded each plug connection with a 10-32 die and replaced the harness with regular wire and crimp-on connectors. I also soldered each connector to make sure I had a good connection.

End of problem.


Regards,

Rick

Received CEL after cold start. VAG-COM reports:
1 fault found:
16764 – Glow plug/heater (Q6) circuit malfunction
P0380 – 35-10 - - - intermittent

TDI details: 2000 Jetta w/auto – completely stock @ 55K miles - first time TDI owner - purchased back in May.

Details: This morning was the first 30°F cold start since my purchase, and therefore the first time noticing glow plug light on for more than a second (in this case ~3 seconds). Car starts normally. CEL appears about 5 seconds later. No drivability problems. Cleared DTC on lunch hour, no more CEL (for now).

Here’s what Bentley reports:
16764 P0380 Glow plug monitoring, No display
• Glow Plug Relay -J52- faulty
• Glow plug faulty
• Different glow plugs installed

I haven’t found any posts on the DTCs, but read lots on Relay 109. Also noticed Bentley interprets “intermittent” as possible loose connection. Will apply grain of salt to verbiage between VAG-COM, VAG-1551 and Bentley CD.

Guess I’ll be probing the glow circuits with a multi-meter this weekend.

QUESTIONS:
Anyone familiar with this fault and/or able to decipher Q6, 35-10?
Any recommendations on testing glow plugs (resistance range / operating current range / etc.)?
Other suggestions?

Click to expand...

It happened about 3 separate times so I tried spraying electronic contact cleaner into the sockets that connected to the plugs.

That worked for about a month. Then the problem was back.

Click to expand...

The problem with regular electrical contact cleaner is it does nothing to get rid of the oxidation. That is the problem with these harnesses. They build up a thin layer of oxidation and cause the resistance variations that are detected by the ECM. You need a contact cleaner that specificlly states that it is alo a deoxidiser. That is why I recommend Deoxit D5. If that doesn't work, then you might want to consider a new harness. But as said, it will happen again with a new harness over time too, so treat the harness once a year or so with the Deoxit to help keep it is good condition. It should be part of a preventative maintenance item, like filter changes & such.

I just had a glow-plug relay replaced on my 04 Jetta with 13k miles. CEL came on when starting cold. Car ran fine, and dealer saw it was an intermittent prob. They gave me a loaner Toureg (Gasser ) for 4 days while they waited for the new relay to come in. No probs since the fix.

I agree.

That's why I threaded each plug and used nuts, washers and soldered connections.

End of problem permanently.

It happened about 3 separate times so I tried spraying electronic contact cleaner into the sockets that connected to the plugs.

That worked for about a month. Then the problem was back.

Click to expand...

The problem with regular electrical contact cleaner is it does nothing to get rid of the oxidation. That is the problem with these harnesses. They build up a thin layer of oxidation and cause the resistance variations that are detected by the ECM. You need a contact cleaner that specificlly states that it is alo a deoxidiser. That is why I recommend Deoxit D5. If that doesn't work, then you might want to consider a new harness. But as said, it will happen again with a new harness over time too, so treat the harness once a year or so with the Deoxit to help keep it is good condition. It should be part of a preventative maintenance item, like filter changes & such.

Click to expand...

Hey Wingnut, I'm up in Sudbury. Where can I get some Deoxit D5? I've been having this problem also and the cold weather is here. T

I used a product called OX-4 made by NSI industries. It is a oxide inhibiter to prevent oxidation between aluminum to aluminum connections and seal out moisture. It seems to work so far (52,000 miles). It is a grey grease.

Just checking back with a status. Used Wingnut's posts (and others) for troubleshooting tips. Found 3 plugs less than one ohm, and one at about 500 ohms.

Received replacement set for $45.80 delivered, but have not installed yet. Will do when the rain stops.

My thanks go out to everyone for their detailed info!