P0605 (DME ROM error) after limp mode

[kgr-e46]

My car went into limp mode on the highway yesterday. Pulled over and restarted the car. SES came on, but limp mode went away and let me drive for ~10 minutes until it happened again. Repeat 4-5 times until I got home.

Checked codes and got P0605 - Internal Control Module ROM Error

Disconnected the battery, cleared codes, drove around today for about 20 minutes without a problem. Then it happened again.

Car starts, runs, and sounds fine until limp mode kicks in. Limp mode will happen after a random amount of time whether the car is sitting ON (not started), idling, or driving.

Has anyone else dealt with this? I was surprised to not find many posts when searching various forums. A straight read of the code suggests a bad ECU, but I read some non-BMW forums where someone had a bad ground or a broken sensor.

And wouldn't a bad ECU ROM cause noticeable problems driving the car and/or make limp mode happen immediately?

Before I send my DME away for repair, or eat the cost of a new one, I'm wondering if there's more diagnosis I can do.

[elrichmeister]

You will most likely need to scan the car with specific scanner that pulls BMW specific codes. Typically codes are pulled with INPA, ISTA, BMW Scanner 1.4, or another workshop scanning tool that can scan all the modules of the car.
It will give you better details with the error codes.

[Shonky]

And wouldn't a bad ECU ROM cause noticeable problems driving the car and/or make limp mode happen immediately?

Before I send my DME away for repair, or eat the cost of a new one, I'm wondering if there's more diagnosis I can do.

Well there's no code set logic for BMW ECUs that I've ever seen so anything goes.

It could be as simple as it doing a ROM checksum and that failing sets the code. If it happens more than x times in a row (or total) then it progresses to the limp mode. ie a one off error doesn't immediately cause a problem.

And because it may be a bit of unused or rarely used code it may not even be a problem.

It does sound like a failing memory device of some sort. A simple reflash might even be enough to fix it. Whilst they use the term ROM I'm pretty certain there's no true ROM. It's all flash.

[kgr-e46]

Thanks. Yeah, the "same error hits a threshold" part never occurred to me.

I hooked up with BMW Scanner and found 5 DME errors -- all yellow (fault not currently present):

====================
0x96 [150] - Internal: Memory test Master / DME memory fault / Control unit self-test, memory test master

Shadow:
0x96 [150] - Internal: Memory test Master / DME memory fault / Control unit self-test, memory test master
0x96 [150] - Internal: Memory test Master / DME memory fault / Control unit self-test, memory test master
0x96 [150] - Internal: Memory test Master / DME memory fault / Control unit self-test, memory test master
0x59 [089] - internal index 240 / Internal DME fault / Control unit self-test, Safety Concept slave check
====================

After clearing the codes I still have:

====================
No errors (green)

Shadow:
0x63 [099] - internal index 246 / Internal DME fault / Control unit self-test, Safety Concept master check
0x59 [089] - internal index 240 / Internal DME fault / Control unit self-test, Safety Concept slave check
====================

It would be nice if a re-flash would fix the problem but that's a bit beyond me. I'm sure the dealer will be happy to take my money. Otherwise, RPM Motorsport said their P0605 service modifies the DME so that it doesn't check/report this anymore.

[kgr-e46]

UPDATE: I sent the DME to RPM Motorsports, who did a workaround for the P0605 issue. Unfortunately, limp mode returned after 5-10min like before.

Their fix worked -- the 0x96 faults didn't appear. There's actually no new faults, and no SES light after limp mode. So that's weird.

I read a few posts about dying batteries causing random issues (including limp mode), and my battery was from 2014, so I replaced it today. With the old battery, voltage with engine ON (not started) was 11.8V, and a slow climb to 13.8V after starting. New battery is 12.6V with a quick climb to 14V.

With the new battery, limp mode didn't come on after 10-15 minutes ON like before. Hopefully a test drive tomorrow goes well.

[Shonky]

I'd be surprised if a battery made any real difference. Remember, when running, a battery is mostly just another load on the alternator.