PD glow plugs 11v???

Hibneck1

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Aug 26, 2017
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Hibbing MN
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04 Jetta PD euh manual trans 205k miles All stock
Hi, I'm a new owner of an 04 Jetta tdi PD with manual transmission. I Bought the car and it has a check engine light on for the number 3 flow plug. I tested ohms on the glow plugs and confirmed number 3 to be faulty. My understanding of the PD engine and all the glow plug recalls is they originally came with 7v glow plugs but then were updated to a 5v plug then again to a different 7v plug. The plugs currently in the car are Autolite 1116 which come up as an 11v glow plug. I thought maybe someone had installed the wrong plugs previously so I tested voltage to the glow plugs and got a reading of 10.7v. So my question is has anyone heard of 11v glow plugs in a PD engine?
 

wonneber

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Oct 12, 2011
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Monroe, NY, USA
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2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
I've never heard of 11V plugs, but I know there are different voltages for them
They cycle the power going to them for this.
I'm not sure if the controller has to match the plug or has to be programed for it.
 

Mike_04GolfTDI

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I think the voltage reading you're getting with your multimeter is deceptive. If I'm not mistaken, the way the car actually simulates 7V is by rapidly pulsing the power on and off. Usually referred to as PWM or Pulse Width Modulation. This is a technique commonly used in electronic circuits as a way to reduce current flow through a circuit.

The voltage rating of a glowplug really just means that's the voltage it can handle without too much current flowing and overheating it. Refer to Ohm's Law to get an idea of how voltage, current, and resistance are related.

So, since the car has a 12V electrical system, and the glowplugs VW chose are only able to continuously handle 7V (or 5V), they have to use something like a MOSFET transistor to rapidly switch the power on and off, limiting the current to a value similar to what you'd have with a steady 7V supply. The current flowing when the power is on is higher than the acceptable amount, but the average over time will be lower, due to the rapid power switching. Heat is what would ruin the glowplug, with too much voltage, so essentially the system is limiting the heat by limiting the current.

Now, when you connect your multimeter to this rapidly switching power source, it's sort of displaying an average, which it sees as 10.7V. If you had an oscilloscope, you could probably see 12V switching on and off rapidly, and then use this complicated BS to work out that it is 10.7V RMS https://en.wikipedia.org/wiki/Root_mean_square which is what your multimeter is probably showing.

In conclusion, I think your car just has the wrong glowplugs in it, but it doesn't seem to matter. As long as they are all the same resistance, perhaps the ECU doesn't throw a code. It probably looks for differences between them to know which ones are bad.

If the car starts and runs with 11V plugs, I'd just do nothing and keep using them. If you have trouble, you might want to try 7V ones. If they burn out, that will be an expensive experiment though.

Edit: Just want to add, if you want to try to analyze the PWM signal without an oscilloscope, read this: https://sonsofinvention.wordpress.c...eriod-and-duty-cycle-without-an-oscilloscope/
 
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Hibneck1

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Hibbing MN
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04 Jetta PD euh manual trans 205k miles All stock
Ok thanks for the reply. That makes a lot of sense. I think I will pull up The scope with my scan tool and look at the pulse width. The car starts fine now but it hasn't gotten cold yet so I would rather be prepared.
 

JB05

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Il.USA
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I'm curious to know what glow plug controlling relay is installed on your '04. It's located under the rain tray on the driver's side. You can get a glimpse of it by looking through the vent holes in the rain tray. Years ago someone here was experimenting with this relay by installing a capacitor in line to up the voltage to 12. I tried this and it actually worked, but the CEL was ON constantly; so I went back to the 7v system.
There could be other hidden DTC's which would require VCDS to read.
 

joep1234

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former '04 Beetle TDI, now 2x '15 Audi Q5 TDI's, 2007 Dodge Ram 4x4 6.7
You can call your local VW dealer with your VIN and they can tell you what the last update that was installed. Good place where to start since they are the only one that can update it.
 

Mike_04GolfTDI

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Mine: 2019 Golf R DSG, Wife's: 2015 Golf Comfortline TDI
I'm curious to know what glow plug controlling relay is installed on your '04. It's located under the rain tray on the driver's side. You can get a glimpse of it by looking through the vent holes in the rain tray. Years ago someone here was experimenting with this relay by installing a capacitor in line to up the voltage to 12. I tried this and it actually worked, but the CEL was ON constantly; so I went back to the 7v system.
There could be other hidden DTC's which would require VCDS to read.
It makes sense that this would work. When the power to the glowplugs is on, the capacitor takes on a charge. When the power to the glowplugs is off, the capacitor fills in this lack of power by discharging through the glowplugs.

The capacitor is counteracting the modulated power that is being fed to the plugs. I suspect this might harm the glowplug relay because more current would be flowing. While the capacitor is charging, the relay would probably see this as a low resistance, almost a short. During the brief pulses of power to the glowplugs, enough current would be flowing to fill in the gaps while the power was briefly off.

I'd be curious to see what the CEL was for. Wouldn't be surprised if it was a code for shorted glowplugs, or over-current. Something along those lines...
 

oilhammer

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Dec 11, 2001
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outside St Louis, MO
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There are just too many to list....
You can call your local VW dealer with your VIN and they can tell you what the last update that was installed. Good place where to start since they are the only one that can update it.

That is not true.

One, because they most certainly are NOT the only ones that can update it, and two, because that recall has long since expired and they needed to be spoon fed information on what/how/why to do it WHEN it was still current. Now, they are generally going to be clueless. You can certainly try, but do not expect a whole lot. Carfax is usually better, oddly enough.

The 11v plugs are wrong, those are for an ALH or AHU/1Z.

The BEW got 7v Bosch originally, then 5v Bosch with a software change, then 7v NGK with another software change. If you still have the original, untouched software from the factory, the 7v NGKs will work fine. These are NOT the same 7v NGK plugs as a BRM came with from the factory. They are a different length.

There is somewhere on here the software numbers for the various versions, which will show up on VCDS. I cannot remember right now which is which, since I generally just put in there what I find in there (5v or 7v) but if the car has 5v I make sure and ask if the owner has any trouble starting in cold weather. If they do, then I suggest updating the software and installing the 7v NGKs.
 

Dunno513

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Feb 1, 2006
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Mirror Lake, NH
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2006 NB PD-TDI DSG
The 11v ALH plugs will work, but don't expect them to get you started below 0 deg F. Mine came with the NGK 7v originally. I never had the 5v update done, nor was I eligible since I had the NGK plugs originally. There is a procedure buried somewhere here to alter the glow settings. I did it but changed it back after not seeing a difference.

I would swap them out for the 11 v during the summers and back to the fragile 7v ceramic during the winter. Recently one of my 7v plugs started to look a bit unhealthy with the ceramic starting to wear down.

I went ahead and ordered the wrong length 7v ceramic plugs which were a crap ton cheaper and they have been working fine and that was 3 winters ago. iirc it was around $40 for all 4 plugs.

They are about 1 cm shorter than the original NGK 7v ceramics so I know the heat is not as robust as the originals in the chamber but they work.. BUT.... I garage park at night and rarely see a neg deg F start anymore. If you are routinely shoveling off snow on very cold mornings, I would sport the $ and get the correct length 7v plugs.
 
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