KI Issues BMW 35i B4: Starter/Battery Problems

Hello everyone,

I've already found some information about AI failures in the 35i B4, but I would still appreciate your expert opinions on my specific problem.

Vehicle: 35i B4, manufactured in March 1996, with AFN TDI engine; Bosch starter motor with 1.9 kW.

Initially, there were occasional LCD clock and MFA (Multi-Function Display) failures during cold starts; this only occurred in very low outside temperatures, and the starter motor also seemed to be working with less power.
With the engine at operating temperature, everything is working correctly... (and there are no other AI-related issues).

--> Battery replacement, as the old one was 5 years old ---> hardly any improvement in the problem .
--> Starter motor removed and inspected in a disassembled state by an electrical engineering company.
--> New brushes/carbon plate installed, as the old carbon brushes were almost worn out.
--> The starter is as powerful as ever, BUT:

--> Still experiencing LCD clock and MFA failures, and very frequently now even with a warm engine .
--> Voltage and current measurement: The battery voltage drops to 10.5V when starting the warm engine; the starter draws approximately 230 amps.
--> According to Arbö, the starter's power consumption (1.9 kW) is too high.

--> Currently, the LCD clock/MFA is failing during cold starts, and occasionally also during warm starts.
--> The main ground cable has been fitted with a new terminal (connector), and the power supply from the starter is also working correctly.

What do you think? Could it be the starter motor; perhaps the winding is partially damaged? Or maybe a glitch in the instrument cluster; electrolytic capacitors in the A pillar?

The AI works perfectly fine during the ride.

I would appreciate any input. I'm not keen on spending €150 on a replacement starter, and the AI might still be malfunctioning afterwards.

Best regards, Roland.

Daffy Duck wrote:

Initially, there were occasional LCD clock and MFA failures during cold starts; this only occurred at very low ambient temperatures, and the starter motor also seemed to be working with less power.. With the engine running at operating temperature, everything is working correctly... (and there are no other AI-related issues). Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. --> The current status is that the LCD clock/MFA fails during cold start and occasionally also during

Hi,

Does the display only malfunction while the starter is running, or does it also malfunction once the engine has started?

Quote:

--> Voltage and current measurement: The battery voltage drops to 10.5V when starting the warm engine; the starter draws approximately 230 Amperes. --> According to Arbö, the power consumption of the starter (1.9 kW) is too high

. For comparison: I measured approximately 220 amps for my ASZ starter (the motor was warm!), but I don't know its rated kW value .

Hello Ulf,

The clock and MFA (Multi-Function Display) fail as soon as the starter engages (when the engine cranks). When the engine is running, the displays usually come back on with a brief clicking sound. Otherwise, there are no other failures, only during startup.

The statement that 230 amperes is too much comes, as mentioned, from the Austrian automobile club ARBÖ...

What I can still understand is that the starter, with the new carbon brushes, seems to be drawing more power than before (I only have measurements from after the change, not from before).

The 109 relay is also new, installed inside... (a moment of hesitation).

Best regards, Roland.

At 10.5V, the alternator should definitely not be failing yet.

How was the voltage measured? With a slow multimeter during a very short startup process? Or properly with an oscilloscope?

You might want to measure the voltage directly at the AI (artificial intelligence) unit using an oscilloscope. It's possible that the battery is providing 10.5V, but the voltage drops significantly at other points in the circuit, such as at the battery connection terminals or the ground cable, to the point where it's only sufficient for the AI unit.

Just out of curiosity: What kind of battery was installed? In this case, the cold-cranking current is much more interesting than the capacity.

Regards,
Guste.

Hi...

How was the voltage measured? With a slow multimeter during a very short startup process? Or correctly with an oscilloscope?

I measured the voltage using a standard analog measuring device, and the ARBÖ (a local automotive association) also had its own measuring device for vehicles... both results were identical, down to the tenth of a volt.



Just out of curiosity: What kind of battery was installed? In this case, the cold-cranking current is much more interesting than the capacity.

Banner Battery, 68Ah, 640A starting current.

Best regards,
Rol

Okay, just one more thing: we should measure the voltage at the AI unit itself or near it (e.g., at the breaker panel connected to the AI) during startup, as I mentioned in my previous post.

Otherwise, my suggestion leans heavily towards using an AI solution. If you're not comfortable implementing that internally, an external diode combined with a large capacitor might potentially provide a solution.

Even so, I still don't fully understand it if the voltage doesn't drop below 10.5V. However, only an oscilloscope Screenshot would probably provide clarification about values above that.

Regards,
Guste.

Okay, I installed a replacement starter motor yesterday.

The first 3 cold starts in the garage (+3°C) were okay; the keyless entry system didn't fail again.

This morning, under the carport and with an outside temperature of just below 0°C, the LCDs were missing again!

Okay, I'm going to start troubleshooting this now. I'll check for cold solder joints and possibly replace the electrolytic capacitors. I'm ruling out the starter for now; even with two different starters and two batteries, I'm still experiencing the same problem, which can't be right.

I praise my Jetta, because since there's nothing inside, nothing can break .

Thanks everyone for your tips!

Sure, here is the translation of the text from German to English:

'LG' is an abbreviation for 'Liebe Grüße,' which means 'Best regards' or 'Best wishes' in English.