compu_85
Gadget Guy
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
(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
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