Relay 109 Engine Computer Power Supply

compu_85 · December 23rd, 2007, 21:10

This thread is a condensed version of the excellent Relay 109 information found in other threads on this site. The other threads have become long, and some of the links no longer work.

(images from schnabba)

What is it?
When you turn the key on in a TDI the relay marked 109 closes and supplies power to the engine computer and some other things. MOGolf provides a complete list of all the things powered by this relay here. All TDIs from 1996 to 2003 have this relay. In 2001 the design was updated and solved a lot of the problems.

What is the failure mode?
When this relay quits working the engine computer doesn't get power. If the engine computer isn't powered the engine will not run. The engine will simply crank and crank and crank. If the relay fails while the engine is running the engine will shut off just like you had turned off the key. When the key is turned the glow plug light will not come on and go out: The glow plug light coming on is the ECU's indication that it is powered up and working properly. If the connection only breaks for a moment you will feel the engine cut out, and see the glow plug light come on for a moment because the engine computer was just rebooted.

How do you fix it?
Replacement is the best method. You can get a replacement relay at many online vendors or at a VW parts counter. The part number is 1J0 906 381 A. The relay simply pulls out.

On the A3 and B4 cars (basically everything before 1999) the relay is located on the relay / fuse panel in the driver's footwell. Remove the trim piece above the pedals to access the relays. One mechanic mentioned some very early 1996 Passats have this relay in the center console area.

Picture of the CEII Fuse box found in the A3 and B4 cars (Courtesy of EtherNut) Relay 109 is the gray one which looks like 601

On the A4 cars (The new beetle and everything after 1999) the relay is located on the relay panel in the dash above the driver's footwell. The footwell trim needs to be removed for easy access. See this HOW TO.

Relay 109 is in position 12:

Image from tongsli

You can see the relay looking between the steering column and the dash trim.

Please note that a replacement relay may be a different color then your original, and the lettering may be upside down. Be sure to plug it in the same direction as the original one.

Why does it fail?
Some of the early relays have poor quality solder connections inside. The connections crack and intermentenly work. This is why sometimes waiting can get the car to restart. The contacts themselves can also go bad. The new, updated parts have larger contacts and better solder joints to prevent failures.

If this can cause the engine to stall, not start, etc, why wasn't it recalled?
Your guess is as good as mine...

Is there any way to prevent the failure of this relay?
As was already stated, VW fixed this problem quietly in 2001. The updated part is gray, and has 109 printed upside down relative to the older black units. The picture of the CEII fuse box above shows an OEM updated relay, the image of the original one fitted to my 99.5 shows one of the problematic ones. If you find your car has one of the original black units it would be a good idea to replace it for an updated one. The cost is very minimal and replacement is easy.

Note that some new aftermarket relays have a black case, even though they have the updated design.

-Jason

maria_beetle · August 4th, 2008, 18:31

The problem I'm having fits this (sort of). Last fall, I had problems starting my 2000 Beetl TDI. My husband replaced the glow plugs and harness wire. This fixed the problems I was having then. Recently, my car began having this problem:
Occaissionaly the glow plug light would not illuminate when turning the key to "on" and the car will not start. This was happening maybe once a month and only when my husband wasn't home to check it out. It started happening more frequently, but after letting the car sit for a while it would stat and be fine for several days/weeks. Now, the glow plug light is not coming on at all and the car will not start. We replaced the Glow Plug Relay tonight with no success. I've read the description of the 109 relay issue and it sounds like the thing to replace but another site said that this relay is either bad or good, no intermittant.
Has anyone has experience with this problem?
The car has over 180,000 miles on it.

DanG144 · August 4th, 2008, 18:34

Replace relay 109. They can fail intermittently, and often do.

DanG

rdkern · August 4th, 2008, 20:34

The relay is either bad or good at one moment. The times it doesn't start it is 100% not good. The times it starts is 100% good.

Replace it.

Have you ever gone down the highway, typically in cruise, and have he cruise "cut out" for just a moment? Typically when it's hot?
Replace it.

gotta go gotta go 109... (repeat, sung to "getti-up getti-up 409..." ) Some may never heard that song. Sorry. Dating myself. It is 99.9% likely the problem.

maria_beetle · August 5th, 2008, 08:26

Thank you, I will see if I can get one today and get it replaced tonight.
I sure hope this fixes it, I love my Bug!!

egibbys · August 5th, 2008, 10:45

[quote=rdkern]
Have you ever gone down the highway, typically in cruise, and have he cruise "cut out" for just a moment? Typically when it's hot?
Replace it.
quote]

Thanks for that. I was wondering what was going on with my cruise control. I checked and I do have the old relay. Will be buying new one soon.

mrGutWrench · August 5th, 2008, 10:54

Quote:

Originally Posted by maria_beetle

Thank you, I will see if I can get one today and get it replaced tonight.
I sure hope this fixes it, I love my Bug!!

__. Hey, MB, the new ones are much more reliable than the originals but they're still carrying a lot of load (electrically). What would be best would be for you to get two (they're reasonably inexpensive) and have somebody show you how to replace the one that's in there now and keep the extra in your glove box. Then, if you ever need to use the second one, you'll have it and you'll know how to do it.

__. It's a really easy job - you ought to know how; you only have to remove two parts, one by hand and one by using a "T-20" -- a kind of "star bit" screwdriver*. Once you have those two parts off (see the first post above and click the red link "See this HOW TO.", follow steps 43-46), you just pull the old 109 out and push the new one in. The new one will only go in one way - the right way. (Oh, yes, your car is what VW calls an "A4" body-model so don't get confused with the A3 instructions.)
(* You can get an inexpensive set of "T-Drivers" [a store clerk might call them Torx-drivers] at most auto-parts stores and "big box" places like da Wahmott and Tar-jay. You are likely to need them in the future and you'll be glad to have them. Just be sure that the set you get includes a T-20 -- it's commonly used anyway.)

__. And since the symptom of the "glow plug" light not coming on is such a tipoff, you'll know when it (if) it ever needs to be replaced again. Think of a spare 109 like a spare tire -- you hope you'll never need it but you'll be glad to have it if you do.

maria_beetle · August 7th, 2008, 07:26

Thank you everyone! It's been two days and this seems to have fixed my problem.

Maria

TornadoRed · August 10th, 2008, 08:03

Quote:

Originally Posted by maria_beetle

Thank you everyone! It's been two days and this seems to have fixed my problem.

Maria

Welcome to TDI Club, Maria.

You folks in Missouri have a handful of top TDI pros (Oilhammer in the StL area, GT aka Glen Temple over by KC, Franko6 down by Joplin).

Maybe update your profile to show what part of the state you're in. And take the time to read as much as you can about your TDI, it will save you lots of worries and money in the future.

coner · August 12th, 2008, 09:44

About 3 weeks ago I had the car into the dealership for a no start (stalling) problem. http://forums.tdiclub.com/showthread.php?t=219890

The dealership replaced the 109 relay and said it was fixed. Fast forward 3 weeks later and now the car won't start!

When I turn the key to the run position I see all the dash lights illuminate except the glow plug light. I donesn't come on at all. After searching the forum I find this to be a typical sysmptom of a relay 109 failure.

I removed all the panels and got to the relay/fuse center. I removed the 109 and tested it by jumping the proper terminals. With no power applied, there is no circuit. With 12V power applied, the circuit is completed.

With the keys out of the ignition, I put the relay back into the holder and hear a click - as if the relay is closing. Is this normal (i.e should the relay complete the circuit as soon as I push it back in)?

Second question, even though the relay bench tested ok, is it possible it is still faulty?

My car is stick in my work parking lot which is a $200 tow from the dealership. They say to bring it in and they look at it and if the newly replaced relay (3 weeks old) is faulty they will replace it at no cost. Although it is still going to cost me the $200 tow to get it back there!

Any suggestions?

Thanks.
Eric

JB05 · August 12th, 2008, 13:13

Stay away from the dealer and find a guru in your location where ever that may be.

TornadoRed · August 12th, 2008, 16:42

Quote:

Originally Posted by coner

Second question, even though the relay bench tested ok, is it possible it is still faulty?

My car is stick in my work parking lot which is a $200 tow from the dealership. They say to bring it in and they look at it and if the newly replaced relay (3 weeks old) is faulty they will replace it at no cost. Although it is still going to cost me the $200 tow to get it back there!

Any suggestions?

Considering that a Relay 109 is a $10 part online or $15 at a parts store or dealership, I would try replacing it again before calling a towtruck.

beetle98 · August 14th, 2008, 13:04

So What next? My car has recently died a few times like key was turned off it started back. I have had a few starts where no glow plug light then eventually it would come on car would start and run fine. Now No glowplug light and no start. So i see this thread and replace the 109 relay with new relay from VW. One in car was already an upgraded relay i noticed. New relay same problem no start what do i try next? just a note I have a aux. fuel pump and normally when i turn key you can hear it come on for a few seconds then shut off until car is started. Now it comes on and just keeps running and no start.

DanG144 · August 14th, 2008, 13:41

beetle,
Why don't you post a new thread in the SouthEast section? Then come back here and post your new thread link. I am sure the guys around here can help you.
DanG

rdkern · August 14th, 2008, 13:47

Quote:

Originally Posted by beetle98

So What next? My car has recently died a few times like key was turned off it started back. I have had a few starts where no glow plug light then eventually it would come on car would start and run fine. Now No glowplug light and no start. So i see this thread and replace the 109 relay with new relay from VW. One in car was already an upgraded relay i noticed. New relay same problem no start what do i try next? just a note I have a aux. fuel pump and normally when i turn key you can hear it come on for a few seconds then shut off until car is started. Now it comes on and just keeps running and no start.

My guess? Grounds. Assuming one of the relay 109's is good, and this happens no matter which is in, a bad ground could cause the power not to get to the ecu. I don't know how your lift pump is wired - could be grounded differently.

I'd clean the grounds and see if it helps. If nothing else, it'll get you in the engine compartment, looking for loose wires.