Merry Christmas and Happy Holidays everyone!

I am trying to diagnose a scary electrical issue with my 2007 E92 330i.

The Main Symptoms:

1. Sudden Power Cut: While driving, the car suddenly cuts throttle/power. At that exact moment, the Service Light flashes briefly, and the transmission throws code CF25 (EGS: Message from engine control Alive signal fault).

• Note: I used to get CF1C, but now it is consistently CF25.

2. Hesitant Crank: When starting the car, the starter turns for a split second, pauses/stops completely, and then continues to turn sluggishly until the engine fires.

3. Sensor Dropouts: My AFR readings (O2 sensor) appear and disappear intermittently.

I really need help, battery voltage is 12.4 when is off, when is on 13.9-14.1 v

And also I was not at home for 19 days and battery was still alive after 19 days so I think its not the battery.

But another problem is when i turn it off and lock it , the park light on shifter doesnt turn off, even after 19 days it was on.

Edited December 25, 2025Dec 25 by twinntrbo

Happy Christmas Firat

Welcome to the Forum

First thoughts a Starter or Alternator issue, here are my thoughts

1. Battery Voltage at rest should be at least 12.5v (lower shows a drain or battery issue) with the engine running 14.6+v (lower would indicate slow or low charge from the Alternator)

2. The fact the car isn't going to sleep (gear indicator still lit)

3. There was an issue with Magneti Marelli starter around your vintage which caused huge Amp draw at start and eventually killed batteries

(1) Fully Charge the battery at the charge points under the bonnet as said should read 12.5+v (2) Needs investigation could be a Can Bus issue (3) Check amperage at start with a clamp Ammeter I saw one that pulled 700+amps

Last but not least get a full Diagnostic scan done using a BMW capable programme best is BMW ISTA/INPA then Foxwell, Autologic iCarsoft or similar. My reasoning here is I can't believe there are not hidden faults particularly as there is a possible can bus issue

We know what you want for Christmas 😅 Have a good one

Dave

Thank you Dave,

Then what do you think about cf25 fault? I tought it was a transmission issue,

Morning Firat

My thoughts are that the trans codes are communication errors triggered by low voltage and or Can Bus issues. How is the transmission running ? Is it sticking in gears ? Are changes jerky ? Any other trans issues leaks etc when was it serviced ?

My actions would be to start with a Fully Charged Battery, clear down the codes check the battery voltage was still at full charge 12.5v minimum

Then put a clamp ammeter on the main starter feed and start the car measure the amps drawn stop the engine and check battery voltage.

As I have BMW ISTA/INPA (I also have iCarsoft BMW V2) I would then run a diagnostic and record all faults I suspect the Trans Faults are not all that are there. Remember a Fault Code very often is a symptom not the cause

Good Luck

Dave

Hi Dave,

I have some critical observations regarding the voltage issues we discussed. I’ve been monitoring the live data via the BM6 app and found a direct correlation between the voltage drops and the car's performance:

• Momentary Power Loss: At the exact moment the car feels like it’s "hitting a wall" and loses power, the voltage at the battery drops instantly to 12.5V while driving. Normally, it stays around 14.2V - 14.5V.

• Transmission Issues: While cruising, the voltage is very unstable, fluctuating between 14.0V, 13.9V, and sometimes dipping to 13.6V. Whenever these fluctuations occur, the transmission shifts become very jerky and harsh.

• The "Reset" Effect: I performed a battery registration via ISTA+ and went for a test drive. For the first 50 km, the car was incredibly stable; the voltage stayed solid at 14.4V - 14.5V, and the gear shifts were flawless. However, after that period, the erratic behavior and voltage drops returned.

• Cranking Voltage: During the first cold start, the voltage drops significantly to 9.6V - 9.8V. Interestingly, if I stop the engine and immediately restart it (without removing the key/terminal 15), the cranking voltage stays much higher and the car starts much "healthier."

It seems like the DME/IBS is losing its calibration or there is a major resistance issue (possibly the ground strap) that triggers these momentary charging cut-offs, especially under load. What do you make of this "temporary recovery" after ISTA registration followed by a relapse

Hi Firat

The fact you get erratic drops in voltage which coincide with your description "feels like the car hits a wall" have you checked the pulleys tensioners and belts ? I have seen 2 instances (1) a frayed belt becoming tangled and snatching when the frayed part caught up (2) The crankshaft pulley rubber isolator breaking up caused a similar effect. The fact voltage drops to 12.5v when you get the effect would point towards the Alternator being stopped momentarily or longer, again check pulleys and belts and the engine earth straps

If you have access to ISTA you should be able to see the Fault Memory for the Engine DME and the Transmission plus all other stored codes

If codes were cleared when you registered the battery (was the Battery replaced or Fully charged) temporarily the car would see no Issues as soon as a fault or the critical fault re-occurred the erratic performance returned.

Dave