Glow plug fault and low battery

D

Dieselfiend

Veteran Member
Joined
Jun 21, 2009
Location
Boise, ID
TDI
1998 Red TDI
I have an MKIII TDI and I'm getting a P0380 glow plug fault. I ohm checked the plugs and all check within spec of each other. Volt checked the harness at all points and I'm getting the battery voltage. I don't get the fault if I've been driving it on a daily basis. However, I normally get it if I haven't driven it in a couple days. I know the battery is getting weak so does anyone know if it's possible to have enough juice to start the car but not enough to keep the relay from tripping a glow plug fault?
 
Mongler98

Mongler98

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Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
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98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Define weak,
Glow plugs don't take nearly any amps compared to the cranking amps of the starter
If i remember right, someone can correct me here, the glow plugs are like 12 amps each MAX but typically don't pull more than 7 each, i think its on a 25 amp fuse.
The starter pulls a massive 145 +/-15. Yes the glow plugs stay on for a good deal longer than the starter will but if you have enough amp capacity to turn the engine over, the glow plugs should have no issues getting enough.
The relay could be the issue.
I pulled up your typical 30/40 relay's specs

Initial contact resistance (at 6VDC 1A): 50mΩ Max.
Operate time (at nominal volt.): 10 msec. Max.
Release time (at nominal volt.): 5 msec Max.
Initial insulation resistance: 100MΩ Min. (DC500V)
Initial dielectric strength:
- Between open contacts: AC500V, 50/60 Hz 1Min.
- Between coil and contact: AC500V, 50/60 Hz 1Min.
Vibration resistance:
- Functional: 10 ~ 55Hz at double amplitude of 1.5 mm
- Destructive: 10 ~ 55Hz at double amplitude of 1.5 mm
Shock resistance:
- Functional: 20G Min.
- Destructive: 100G Min.
Endurance (operations):
- Mechanical (at 7,200 ops./h): 10,000,000
- Electrical (at 600 ops./h): 100,000
Ambient Temperature: -40°C ~ +125°C (no condensation)

So your relay should be able to contact with only 6 volts and if your battery has only 6 votls, you are NOT going to be able to start the car lol
I would start with swapping the relay and if that isnt the issue Check all the connections between the harness and the fuse box and relay. MK3's have a bad habit of developing a weak contacting point for relays after 20 years of life! I have seen countless connections under hoods of various cars that had a bit of water get in to it from age of the seals, the connections gets corroded and only shows issues when hitting a bump or in my ford escapes situation, if it sits in a rain storm parked.
Its also possible for the glow plug tip at the connection or inside the harness to have a not so snug fit.
 
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T

ToddA1

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Aug 3, 2011
Location
NJ 08002
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'96 B4V, '97 B4 (sold), '97 Jetta (scrapped)
GP fuse is at least double 25A.

I’d try cleaning the contact points of the GPs. May just be the monitoring that’s throwing the code. Cheaning cleared my code.

-Todd
 
D

Dieselfiend

Veteran Member
Joined
Jun 21, 2009
Location
Boise, ID
TDI
1998 Red TDI
Mongler98 said:
Define weak,
Glow plugs don't take nearly any amps compared to the cranking amps of the starter
If i remember right, someone can correct me here, the glow plugs are like 12 amps each MAX but typically don't pull more than 7 each, i think its on a 25 amp fuse.
The starter pulls a massive 145 +/-15. Yes the glow plugs stay on for a good deal longer than the starter will but if you have enough amp capacity to turn the engine over, the glow plugs should have no issues getting enough.
The relay could be the issue.
I pulled up your typical 30/40 relay's specs

Initial contact resistance (at 6VDC 1A): 50mΩ Max.
Operate time (at nominal volt.): 10 msec. Max.
Release time (at nominal volt.): 5 msec Max.
Initial insulation resistance: 100MΩ Min. (DC500V)
Initial dielectric strength:
- Between open contacts: AC500V, 50/60 Hz 1Min.
- Between coil and contact: AC500V, 50/60 Hz 1Min.
Vibration resistance:
- Functional: 10 ~ 55Hz at double amplitude of 1.5 mm
- Destructive: 10 ~ 55Hz at double amplitude of 1.5 mm
Shock resistance:
- Functional: 20G Min.
- Destructive: 100G Min.
Endurance (operations):
- Mechanical (at 7,200 ops./h): 10,000,000
- Electrical (at 600 ops./h): 100,000
Ambient Temperature: -40°C ~ +125°C (no condensation)

So your relay should be able to contact with only 6 volts and if your battery has only 6 votls, you are NOT going to be able to start the car lol
I would start with swapping the relay and if that isnt the issue Check all the connections between the harness and the fuse box and relay. MK3's have a bad habit of developing a weak contacting point for relays after 20 years of life! I have seen countless connections under hoods of various cars that had a bit of water get in to it from age of the seals, the connections gets corroded and only shows issues when hitting a bump or in my ford escapes situation, if it sits in a rain storm parked.
Its also possible for the glow plug tip at the connection or inside the harness to have a not so snug fit.
Click to expand...
Your logic makes perfect sense. Just can't figure out why it would always happen under a low battery condition. By low, I mean falling slightly below 12V. I feel like this is a relay issue.
 
Steve Addy

Steve Addy

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Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
So is the battery discharging (under 12v) at idle? Or is the low battery when it's being checked with volt meter when the engine is off?

If your battery is anything below 12v even after you've had it on a battery charger for a while then it's basically dead. Batteries will have standing voltage of 12+ volts, I think all mine are in the range of 12.5v or better.

I'd take a hard look at that GP harness, those can get brittle and fall apart pretty quickly. I know the one in my mk3 has some big cracks in it.

Steve
 
Mongler98

Mongler98

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Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
yea, 12.4 is iffy, 12.2 is relaly bad.
Batteries die int he summer and you find out in the winter, is the old saying.
12.6 is fine and 12.8 is premo.
You KILL batteries the fastest when they fall below 1/2 of a charge. never drain a battery lower then 12.2 volts if you want them to last. i have plenty of AGM's on varius fisshing boats. you never draw a battery that low and expect it to last very long. 12.2 is about 40-50% of a full charge.


What voltage is the battery at when your cranking it after its fully charged? anything lower than 10 is no good
 
D

Dieselfiend

Veteran Member
Joined
Jun 21, 2009
Location
Boise, ID
TDI
1998 Red TDI
Steve Addy said:
So is the battery discharging (under 12v) at idle? Or is the low battery when it's being checked with volt meter when the engine is off?

If your battery is anything below 12v even after you've had it on a battery charger for a while then it's basically dead. Batteries will have standing voltage of 12+ volts, I think all mine are in the range of 12.5v or better.

I'd take a hard look at that GP harness, those can get brittle and fall apart pretty quickly. I know the one in my mk3 has some big cracks in it.

Steve
Click to expand...
The standing voltage of the batter is definitely below 12. I'm sure it needs to be replaced. However, my initial question is if that could cause a GP fault. The GP harness is good. Just replaced it a few years ago and inspected it again just to make sure.
 
D

Dieselfiend

Veteran Member
Joined
Jun 21, 2009
Location
Boise, ID
TDI
1998 Red TDI
Mongler98 said:
yea, 12.4 is iffy, 12.2 is relaly bad.
Batteries die int he summer and you find out in the winter, is the old saying.
12.6 is fine and 12.8 is premo.
You KILL batteries the fastest when they fall below 1/2 of a charge. never drain a battery lower then 12.2 volts if you want them to last. i have plenty of AGM's on varius fisshing boats. you never draw a battery that low and expect it to last very long. 12.2 is about 40-50% of a full charge.


What voltage is the battery at when your cranking it after its fully charged? anything lower than 10 is no good
Click to expand...
I know the battery is bad. But again, would that cause a GP fault? I only get the GP fault after the car has been sitting for a couple days and experiencing some parasitic draw. When I put the key in start position, everything dims while the GPs are on. It seems to start ok but definitely need a new batter.
 
Steve Addy

Steve Addy

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Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
Don't know whether the GP system is working right or not but trying to diagnose a problem with a known bad component (battery) you're not going to get anywhere. You have no idea what impact the inadequate battery is going to have on the system.

Having said that it's probably safe to say the battery has insuffient voltage to power the GP's, which might trigger a fault. The dimming lights would suggest that it's being taxed.

The best practice would be to replace the known bad component and see how the GP's respond to that, if you've tested everything before this it would probably be safe to assume that the error will correct itself once a new battery was installed. If it doesn't then at least you can rule the battery issue out as a culprit.

Good luck

Steve
 
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