02 ALH glow plug relay

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
Okay, so my junk keeps giving me CELs about the #2 GP being bad. I've used my volt meter to test them all, working up to the point of just unplugging the relay and using the amperage range on the meter I got 15A on all 4 of them.
One lead on the battery positive post, the other on the pin in the relay connector. So I know everything else in the system is fine and dandy.

So I looked around and I can get a new bosch relay for $45ish through work. Figure hell, what's there to lose and took mine apart to see if I could screw with it.

Put a couple razor blades in the tabs and got the innards out, and sure enough there ain't no relay contacts. There are three power transistors though. Simple enough and kinda cool that they went solid state. All three test good, so I look a little further and sure enough there's an aluminum spacer in the buss bar on the drain of all 3, and it came that way intentionally. For whatever reason they don't want #2 to have a transistor directly feeding it, but instead they have the thing feed power to it through the circuit board and then up along another bus bar to the connector.

They also have 4 SMD resistors (1 K ohm) from each GP pin on the non transistor end of the bars to the GP controller chip. They must measure volt drop across the bars to see if one's drawing less current. All good and ****, except that one of them has a slightly longer path before that resistor, and sure enough it is the one that keeps giving me ****.

So, do I add another NPN power transistor to it, or just tie all 4 bars together at the "volt sense" trace?

I'm leaning toward the option that makes the controller "dumb" and think that all GPs are good all the time.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2005 BEW Wagon
You could re-engineer the module, but in my view it's probably just coincidence that your problem glow plug has a slightly longer circuit board path, since there are millions and millions of these relays in circulation, and you'd expect a systemic design problem to be well known by now... 12 years later.

Also, I think you probably want the diagnostics to work. Any of us that used to run IDI engines back in the day would have killed to have something tell us of glow plug problems *before* we discovered said issue.. on a very cold winter day. :)

My point: might be worth considering if you've exhausted getting the system to work as designed.

For instance: the resistance of the glow plugs. If they are measured carefully the chances are reasonably good that you will find the errant one has a slightly different resistance... enough to trigger the module but not enough to be detected on a 0-15 A scale when measuring current. :)

The other common cause of a good set of glowplugs triggering a CEL is buildup of corrosion at the harness-to-glow plug connection. A spray contact cleaner like De-Oxit is the standard thing to try here.

Just my thoughts,

Vince
 

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
For instance: the resistance of the glow plugs. If they are measured carefully the chances are reasonably good that you will find the errant one has a slightly different resistance... enough to trigger the module but not enough to be detected on a 0-15 A scale when measuring current. :)

The other common cause of a good set of glowplugs triggering a CEL is buildup of corrosion at the harness-to-glow plug connection. A spray contact cleaner like De-Oxit is the standard thing to try here.
Measuring the impedence is the only way to really see what they're doing, the resistance changes wildly as they heat up. Besides, all four ohm out to .8 ohms from the GP relay connector.
I've pulled off and put back on that plastic dealiemabob at least ten times. Should have cleaned the contacts from that alone.

The diagnostic feature is only really there in my mind for people who get in their car and expect it to go. Barely know how to put gas in the tank and definitely don't know how to pull the oil dipstick.
My 7.3 has had a couple bad GPs for a while, know how I can tell? You can hear it jump while cranking when it finds a "hot" cylinder, and lights off when it finds a few in a row, then it runs rough until they all start to light off.
I don't like that it lights up the CEL for me to ignore. Just got the airbag light off by sticking a 470 ohm resistor in the connector for the seat belt switch (someone had cut the wires at the seat belt latch)
 

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
Okay, loaded up the thing in winOLS and started searching for the code numbers, then disabling them. Everything relating to the GP relay and GPs got disabled, little oddity with the individual GP codes though...

17055 01649 00002 65535 08960 The first four are the ones that correspond to the cyl 1,2,3,4 GPs
17056 01650 00002 65535 08960 Curiously enough the last of the four does not fit the mold set by the others
17057 01651 00002 65535 08960
17058 01652 65535 00000 08960 These two are probably here because the GP controller's good for 6 cylinders.
17059 01653 65535 00000 08960
17060 01654 00002 65535 08960
Then the one in red fits the pattern of the three in blue, but is not in proper sequence with the fault code number (the first column), if it were to display on the scanner, it would be GP number 6, but curiously enough disabling it disables the GP #4 (or maybe #1) code.

Made them all fit the green pattern and unplugged the GP control box. Stripped the board in it of everything but the transistors. Added a resistor from ground to the FETs' gate to make sure they stay off when I want them off, then hooked up a pushbutton to put juice to the gate pins when I want GPs. Works great, and no GP light.
 

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
Finally killed the FETs in the box of wizardry after all this time. They failed closed, as they are wont to do, killed my battery a couple times. Kind of surprising how well these GPs last, coming from ford IDIs that run 7V glowplugs that burn themselves out pretty regularly.

Might wire them up to a normal relay, might just not run GPs, not like I really ever used them apart from push starts anyways.
 
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