My reverse light on my 01 a4 1.8t has not been working for a while. I took it by my mechanic today because I thought it was the reverse light switch and he seems to think the transmission has to be dropped to get to the top of the transmission where one end is plugged in. He's only going to charge me $250 to do it all. He thinks it's the switch because fuse 31 for the reverse lights keeps blowing anytime it's plugged in.

Does anyone know if the tranny has to be dropped for sure? if not how can we get to the top of the transmission for the plug?


Audi B5 A4 Quattro 1.8T > Search > Reverse > ES#266380 Reverse Light Switch With O-Ring - 012919823F

 

really could use some help on this, someone has had to have done this at gone through something like this at some point.

 

I don't think you have to drop the transmission to do this. You can easily acess the plug for the reverse lights through the driver's wheel well. There should be two plugs near each other on the case of the transmission. One goes straight into the case near the driver's front CV (this is the vehicle speed sensor), the other has a wire that goes to the top of the transmission (reverse light switch).

Before you pay a mechanic, I would jack it up and pull off the driver's front wheel. Find the plug for the switch. There should be 2 torx screws that hold the plug to the transmission. You can undo these to gain better access. Jumper the two pins on the engine side of the harness and turn the key to the "On" position. If all else is well, the reverse lights should be on.

Put the transmission into reverse and use a digital multimeter to test the resistance of the switch. With the trans in reverse, you should have close to 0 ohms. Pull the trans out of reverse and test the resistance again. Now it should read infinite (usually designated with a "1"). Since you're blowing the fuse, you can also test resistance to ground. Check from one pin on the switch to the transmission case. This should also be infinite. Repeat for the other pin. Try for both the trans in reverse and any other gear.

 

Since i have a blown fuse will I still have reverse lights if I jumper the plug? I just tried jumpering the two connections on the plug and put it in reverse and didn't get any reverse lights, but I figured it was because I have a blown fuse?

 

Yes, you'll need to replace the fuse. Sorry, I should have put that in the procedure.

 

I should also note that while at the mechanic anytime we replaced the fuse and started the car it immediately blew the fuse.

 

Does the fuse blow when the switch is unplugged? If so, you've got a short somewhere else.

 

When I run out to the store later I'm going to grab some fuses so I can test it. I'll update once I try it out.

 

Another thing you can do is to unplug the switch and use your multimeter to test for shorts in the rest of the harness. Touch one lead to the load side of the blown fuse and the other to some bare metal on the chassis somewhere. With the switch unplugged, you should see infinite resistance. If you're not sure which side is the load, test both. Neither should have a path to ground. Should save on fuses.

 

I got the new fuses, unplugged the switch from the motor side, plugged the fuse in, turned the car on and it didn't blow. I then jumpered the motor side plug and through it in reverse and i had reverse light so this means it's the switch right? if so does anyone know how to disconnect the switch from the TOP of the transmission? does the transmission have to be lowered?