chickenpizzawith

I'm back here, and I will follow the suggestions provided.
To get started, I built a janky solution to be able to test the relay connected to the car.
I attached all the leads to the relay and tested the voltages. A video is worth a thousand words: https://imgur.com/a/tBHnsKf
Then, I jumped the relay again by connecting 30 to 87 with alligator clips, and once again, the car turned on within a second.

The bad news is that no voltages change when I turn the key. It's exactly the same as measured in the video, which indicates the relay the signal is never coming to the relay to close it.
There was a suggestion that it could be the Start/Stop, and now with the car on, this is the message I'm getting:


Honestly, I can't promise this is the first I've seen a message. Of course, it's related to this, but it seems like a warning I get after removing the battery.

thecajunboy

Sorry but the video is near useless without knowing what terminals you are measuring.

Do this:

1. Measure from terminal 86 on the relay to chassis ground while turning the key. I asked you earlier to do that and you're not going to get anywhere until we know what's going on there.
2. If you get 12VDC in Step 1, then measure from terminal 85 to chassis ground while turning the key.
3. Forget about terminals 30 and 87. You've proved that portion of the circuit works.
4. Post the readings from steps 1 & 2 and we'll go from there.

chickenpizzawith

Thanks for the patience! I've tested everything.
With the relay unplugged and just testing the terminal directly from the relay box, I get:

Terminal 86: 2.42V
Terminal 85: 0V

This does not change with the key out of the ignition, with the key in, with the ignition on, and with the key turning. All the same values.


Now, if I do the tests with the relay connected, I get these values:
Terminal 86: 2.42V
Terminal 85: 2.42V

Same as above, it does not change if I'm turning the key or not. Both terminals are getting the constant voltage.


As a repeated test to prove some basic parts are working, I connected all the wires to the relay and used a 9V square battery on Terminal 86 and 85, and the car turned on. So, as mentioned above, power in and out of the relay is working, and so is the relay itself.
As you're trying to point out, I'm not getting the right commands on 86 and 85.



If it matters, with the car fully on and the engine running, I get the same 2.42V on 86 and 0V on 85

chickenpizzawith

If it matters, these are the devices under the lining in the frunk:

Driver side:






Passenger side:

chickenpizzawith

I spent some more time with the car today. There are some promising findings. They're really relevant, or it's more bad news.

I removed the driver's seat and carpet; it was humid underneath. The connections to the immobilizer are corroded. They seem to be making a good connection, but it doesn't look good.






I unplugged everything and used contact cleaner, and everything came out pretty easy. I was hoping that would be the issue, but alas, the car still didn't turn on. I will re-clean it as a last-ditch effort.


Then I went back to the 433 starter relay to see if I was getting any different values, but they were exactly the same. I'm getting 2.42v at the posts. There is no signal to close the relay. A new thing that I tried was to jump the relay with a 9V WITHOUT turning that key. That also works, I don't need to turn the key to trigger the starter. I can pretty much hot-wire the car with only having the key in the ignition.
My current hypothesis:
1) Short in the wires that should close the 433 starter relay
2) The ignition switch is not sending the command when I turn (However, the dashboard knows when I turn the key because it asks me to step on the break)
3) The relay commands are getting mixed somewhere
4) Some computer died (immobilizer? DC? I'm struggling to test those)

thecajunboy

You're sort of on the correct path, but relay commands are not getting crossed. That 2.42 VDC needs to get to 12 VDC, and the DME also has to switch the circuit to chassis ground. At this point I think it may be a good idea to find someone with a PIWIS that may be able to help read the faults and coding of your control modules. With the battery below sufficient voltage for extended periods there may be an issue in one or more modules.

Do you have 2 keys? Both fail to start the car? Both can lock and unlock the car electronically?

That module is under the driver seat? I'm not finding any info on that.

chickenpizzawith

I have 2 keys. One has never been used. I replaced both batteries but no work.

regarding the relay voltage, I read somewhere the starter relay receives some low voltage when the key is ignition so the car can test things are working. Like a signal. Then when you turn the key it goes to 12V.

the part under the seat is the immobilizer, I believe. I will try an extra clean tonight. It was very wet there.

thecajunboy

No, the module under the driver seat should be the Rear Body Control module. Three of the four wires should have 12 VDC at all times. See snip of the circuit below. Should be easy to measure, but your problem is not with this module or wiring. Terminals D1, D2, D3, D4.

chickenpizzawith

Checking these now. While you posted, I went to re-test the keys.
I made a couple of videos. They don't add new information, but it's a better demonstration of the symptoms.
Keys and behavior: https://i.imgur.com/dqkKcoc.mp4
Part under the seat: https://i.imgur.com/Ihxl3Ia.mp4

thecajunboy

If you still haven't solved this yet, here's something else to verify.

From the starting process I posted earlier.
• The DME, via CAN from the PDK controller, verifies the Gearlever is in Park or Neutral. Once the “brake pedal is pressed” message is received from the PSM controller the DME switches the T85 connection of the starter relay to earth.
• The EZS detects the key is turned to crank (T50) the Front BCM supplies ____ volts to the T86 connection of the relay. The relay is activated and the starter solenoid receives a supply via the T87 connection of the relay.

See wiring below. I've bubbled in the relevant wiring. Easy way to check would be to just observe the brake lights when the pedal is depressed. If that is good, we can hopefully assume that the signal is also making it to the DME, which is the important part of the circuit you're having issue with.

thecajunboy

OP, any luck with this? Looks like you may have signed up just to get some help with your problem. That's okay, and if you don't stick around, that's okay too, but it would be nice to know if any of this helped, or what you or a service tech eventually found. Lots of folks around here search the posts for help and this would be one of those that could help if we get some closure here.

chickenpizzawith

Thank you for checking on me. No, the problem is not solved yet; I was traveling this week and haven't checked the car. I understand that many people read these for similar issues, so I'm compiling everything in a more readable and SEO-friendly post so other people can follow along and see if it helps them.
Unfortunately, I'm still stuck in the same loop, getting no response from the car. I assume my next step is getting better at checking the wires themselves. Some of these assemblies (like relays and fuses) need to be removed so I can check the connections in the back.
One long-shot blind hope I have is that a week of airing in the garage might dry any wet contact I have. I will post an update and more indicative and helpful photos later this week.

Cheers, and once again, help for the support! I will need more =)

Aakash Shah

you ever figure out the issue?