Hi all,
So tonight my car suddenly no longer started up. It had literally been driven within 5 minutes and suddenly no longer started, yet it cranked healthy. No problems, no lights, etc.
Thus, I suspected fuel system related since our lovely beasts seem to have several known failure points - that the fuel tanks are no longer being balanced somehow and the tank your fuel pump is in empties; that the fuel pump has died; or that the fuel pump relay has gone bad suddenly.
To figure out what the problem is in 10 minutes with your bare hands and a piece of copper wire, here's my guide to what I did (Big hat tip to Rao):
1. Step one: Put key in position 2 so that everything is powered up, put your seatbelt on, and then open up your secret menu on your gauge-cluster and go to test: 05 or 06 (forget which) and look at your tank levels to confirm they are at least close to each other:
2. If your levels look equal and sufficient in quantity, next up is testing your fuel pump and fuel pump relay together. For this, you'll need a ~6" piece of copper wire or similar.
3. Open up your trunk and pull open the right-hand access panel behind the right taillight. You'll see a row of box-relays as such - the TALL BLACK ONE is the fuel pump relay. See below:
Now, if you have someone with you, put your hand on the fuel pump relay while they turn the key to position 2. If the fuel pump relay is working, it will notably click under your hand - you won't miss it. If the fuel pump relay is dead, a lack of a click is a clear indicator. However, most people don't have individuals with them, soo....
4. Here is the fuel pump relay pulled out (just tug and wiggle a bit and it'll pull out with some force)
5. Now you want to access what the relay plugs into - that grid underneath it and the wires that feed that grid. Pull the grid straight out and it'll unlock from it's slot and give you a few inches of room to manuever it around.
6. Going into this relay is ~4 wires. 2 thick wires and 2 thin. The 2 thick wires are red & violet stripes and red & white striped.
AFAIK, these represent power supply to the relay and then a power wire that runs to power the fuel pump - they become connected when the relay is signal'd to connect them.
To test the fuel pump and relay, you want to stick the wire in the grid-slot that connects to the thick wires (one red-white striped, one red-violet striped). You'll need to really jam it in there to make contact. Even with no key in the car, this has power with the trunk open. When your make-shift wire makes contact on both ends and connects these power supplies, you may see a spark and, if the fuel pump is working, you will hear it begin whining/pumping as long as you maintain contact - it won't cycle on/off, because it not has a steady supply of power.
If the fuel pump does not turn on now and cannot be heard, it is dead. If it does turn on and you can hear it, keep the wires in contact and either start the car yourself or have someone else start the car. If it fires up, your fuel pump relay is dead.
...
Hope this helps others. Ironically, I've been eyeing up the fuel pump/filter/relay kit for a solid month and just putting it off since the car was running fine. And then tonight, my fuel pump relay dies. Time to pony up.
Thanks to this wonderful community and Rao in particular for making it possible for a basic DIYer like me to narrow this down to a specific relay at night, with a flashlight, and pretty much no tools.
10Likes
. Plus as mentioned BMW goes it's own way with relay pin orientation. That is why we went with the colors and gauge.
Linear Mode
