Transission Warning Light - Tons of codes - No Limp Mode??

[ToXiC]

Encountered an annoying issue with my '09 N54 135i.

Intermittently it will completely die while driving - 0 power to the drivetrain, no power steering, no limp mode. Transmission warning light comes on (yellow cog ) and the windhshield wipers start going nuts.

After waiting a few minutes the car will generally start up fine, and then the problem happens again in a few miles.

I got it looked at and ended up getting the battery sensor replaced, but clearly that didn't fix it.

I pulled up the codes the last time it happened and there are quite a few, not entirely sure what to make of this:

29DC - DME: Cylinder injection output
2A2D - DME: Fuel low-pressure system, fuel pressure
2E7F - DME: EGS via PT-CAN2 and PT-CAN
2EFE - Electric fan, activation
CD95 - Message(operation, cruise control/ACC,0x194) incorrect, receiver DME, transmitter DSC
CD98 - Message error (DSC torque request, 0xB6)
CD99 - Message (torque erquest, EGS, 0xB5) incorrect, receiver DME, transmitter EGS / HIM / SMG / DCT
CD9C - Message (speed, 0x1A0) incorrect, receiver DME, transmitter DSC
CD9D - Message (transmission data, 0xBA) incorrect, receiver DME, transmitter EGS/HUM/SMG/DCT
CD9E - Message (transmission data 2, 0x1A2) incorrect
CDA1 - Steering wheel angle 0xC4 incorrect
CDA5 - Message (status, DSC, 0x19E) inorrect
CDB0 - Message error (display, transmission data, 0x1D2)

Anybody else run into anything similar? Kind of seems like electrical gremlins so the battery/sensor theory seems plausible, but considering the sensor was just replaced and the battery is only ~4 years old......

[blue135]

Modern Cars are very sensitive to Battery voltage & Current and they react weirdly so do not rule out a battery issue. I know of instances with very strange electric gremlins on. Chevys from 2010, Fords from 2021, Bmws from 2008, etc, though none involved cutting off engine power.

[tracer bullet]

Will agree that our cars do seem to go completely nuts when there's a battery issue. Many posts over the years with a million new codes suddenly popping up, and a new battery or cable fixed it.

No guarantee that's it, but it's something to look into.

* Battery itself
or
* Cabling - many points it can corrode or break

How old is the battery? Has it been checked out recently (i.e. bench test)? Guessing Vancouver is cold this time of year, that won't help either.

[ToXiC]

New development - got a new battery installed and the problem seemed to temporarily be fixed. But a few days later it now won't start at all, seems to be the same set of codes again 🤔

[ToXiC]

So I found this thread that seems like it could be the same issue: https://www.e90post.com/forums/showthread.php?t=1934018

Got the ol' multimeter out and when connected to the +ve post and the chassis it was reading ~12.3. Connected the negative to the oil filter housing and it was only reading ~5v. Got the flashlight out and sure enough it looks like the ground strap is green, so definitely on its way out...

[ToXiC]

Somehow must have been reading the multimeter wrong. Its now showing 12v across the engine and chassis so doesn't seem to be a grounding issue.

To summarize:
- Car wont start
- Tried jump starting the car from the engine bay
- Voltage across the b+ post and chassis as well as engine seems fine
- Connected jumper cables from chassis to oil filter housing to rule out ground issue - car still didn't start
- When trying to start there are two clicks that sound like they are coming from the alternator/engine but the starter doesn't seem to be making any sound.

I don't want to rule out an alternator or starter issue but it seems odd that when I first started having issues, the car was dying while driving. To me that doesn't sound like a starter. And I wouldn't expect the alternator to prevent the car from starting if the battery is currently fine.

Any other troubleshooting ideas?

[ToXiC]

After coming across a few similar posts where the CAS module kept coming up I came across this video:

I removed the terminal 30g relay and reseated it, and voila, the car starts now. I placed an order for a new relay just in case.

Once the car started I checked the voltage under load and noticed the alternator seems to be getting awfully close to outputting 15v. It hovers around 14.8-14.9. Perhaps it was overcharging and thats what fried my IBS, previous battery, and perhaps started to do damage to the relay?

Its interesting that in all my googling nobody ever mentions the CAS relay for our 1 series/ e88/e82 vehicles. Always e90. Hopefully this post can help others with the same issue.

Anyways, seems like next step is to figure out whether the alternator is on the way out and whether it may have fried anything else.

[tracer bullet]

I'd still keep an eye on the cables. Some green corrosion (because it's copper) can be OK. But if it's really bad then all bets are off. Maybe check the connections and make sure they look OK.

You can get great voltage through almost anything. A wire the size of a human hair can carry 15 volts. By itself it doesn't guarantee a strong start for the car. It's the amperage that is the question.

You may have solved the issue, hopefully so. But the voltage alone doesn't guarantee a good cable.

9 / 10 times it's the battery or a cable. So if you did find the issue you did a pretty nice job. Maybe it should get mentioned, but typically that's not it. That's why we are all here though! If you see someone else with a similar issue, certainly mention it.

[charles1442]

hey have this exact issue, any way I can contact you?

[ToXiC]

It's been a few months now and after putting in a new CAS relay I haven't had any issues since. Im guessing it was a combo of bad battery/cable and CAS relay. Maybe some sort of chain reaction of them going bad 🤷*♂️