Audi A4 Starter Motor Problem: Won't Crank/Stuck

Happy New Year to everyone!

Regarding the issue with an Audi A4, B7, 3.0 TDI engine (code ASB), approximately 230,000 km.

Because the starter motor was running slower and slower, eventually stopping completely, I replaced it!

Everything is great, the starter motor spins quickly, all good.

After approximately 4 weeks, the problem of the engine failing to start recurs, with the starter motor stopping but the engine continuing to turn over intermittently, regardless of whether the engine is cold or warm.

It's scary because it sounds like the engine wants to turn backward or is about to seize completely.

Does anyone else have the same problem, and perhaps a solution?

Hi there,

"Edit: I was somehow thinking of the A6 model when I read that... If the B7 has the battery in the water tank, then the cause is probably something else."
/edit

Take a look at the wiring leading to the starter motor in the engine compartment. At the positive terminal where you connect for jump-starting, high resistance can develop due to corrosion of the crimp connections. Replacing the cable usually fixes this. I'm not entirely sure, but the wire might also be disconnected and screwed together inside the fuse/relay box on the passenger side, within the water reservoir. Water tends to accumulate there, which can also lead to corrosion.

Best regards from Berlin.
olli

Is the battery okay?

Starter motor: Bosch, Valeo, or cheap junk?

Automatic or manual transmission?

Hi!

Transition resistances in the battery cables can be easily and quickly identified without having to take measurements.
because these areas get hot.

It's really great if you can borrow a thermal imaging camera from work or acquaintances.

While I haven't personally held one before, electricians often use them when performing inspection work inside electrical panels.
It should work very well.

Does the tension break when he gets blocked?

Yes, everything is short-lived; sometimes he continues if you have the courage to stay engaged.

A colleague who is a certified automotive mechanic told me that he recently read something about how the starter motor can have difficulty starting in cold weather due to the cold grease on the shaft/gear. However, this was specifically related to a T4 diesel engine.

If the starter is new and from Bosch, it's probably not the cause. Now we need to try to figure out whether the voltage drop is the cause or the result of the problem...

Occasionally, fully charge the battery using a good quality charger for 24 to 48 hours.

Hi there,
Disconnect the battery and measure the resistance from the positive cable to the positive terminal on the starter motor. Trace the cable from the battery and check if it's split or connected with a crimp or screw connection somewhere along its length.
"If there's a spot like that, try touching it after a failed launch attempt; it might get quite hot."

Best regards from Berlin.
olli

Hi there,
where exactly was it measured (if at all)?
Voltage at the starter motor, voltage at the magnetic switch?
hg
Herbert.

Hi, I haven't measured the voltage yet.
I just ordered a new battery (original).

If that doesn't help, then we'll try connecting a different cable directly from the battery to the starter motor and see what happens.

You're throwing parts at the problem.

over-boost wrote:

If that doesn't help, then another cable will be connected directly from the battery to the starter motor, and we'll see what happens.

Hello.

Don't forget the large grounding cable from the body to the engine block. Even if it looks fine on the surface.
I'm familiar with this problem from the ASB (Automatic Speed Limiter) in the Audi A6. The cable is located on the passenger side, near the front, and runs underneath the exhaust manifold.
It forms a slight downward curve and then rises again towards the motor, which is why capillary action draws moisture (rain/saltwater) behind the insulation, where it remains and "works" to promote oxidation.
If you bend it back and forth repeatedly and it starts to crackle inside, there's not much conductive copper left.

Regards, Mpire.

Good morning, quick update.

New original battery installed.
Still experiencing the same symptoms.

The thick positive cable is routed directly from the battery to the starter (AL) in the A4. It appears to be okay visually and after a check for proper mounting, bends, and tension. Furthermore, it's also covered with an additional thicker plastic sheath!

The short negative cable, connecting the body to the motor, also seems okay. The connection is very secure, and the cable has good flexibility and strength.

- SO, even today, during the cold start in the morning WITHOUT preheating (otherwise always with preheating), the starter motor runs fully, stops briefly, and then after about 1 second, simply continues turning if I hold the ignition key all the way to the right (boldly).

Hi there,

It would be helpful if you could take measurements of the resistance between the motor block and the chassis, as well as the resistance between the positive terminal and the starter.

Best regards,
olli

Hi there,
It's quite frustrating that you're ignoring all the suggestions for providing measurement values. We are repeatedly asking for resistance readings and voltage levels. Don't you have a multimeter?

To summarize the information:
- It's about an Audi A4 B7 with an ASB engine.
- The vehicle has an ignition switch with a key that can be turned to the "off," "ignition on," and "start" positions. The "start" position is spring-loaded and returns to the "ignition on" position when released.
- The positive battery terminal and the starter motor are directly connected, with no ignition switch in between to interrupt the battery connection.
- The battery negative terminal and the vehicle's chassis are directly connected, with no Battery Management System (BMS) in between for battery monitoring.
Correct?

The next step is to determine what type of electronics is located between the ignition switch and the magnetic switch in this particular model.

Du schreibst einmal "...alles kurz tot...", jetzt schreibst Du "...stoppt kurz, dreht nach ca. 1 sec einfach weiter..". Das erste heißt für mich alle 'Lichter aus, das zweite nicht. Wis that correct?

hg
Herbert.