2007 Scion TC Alternator

Hey guys!

I was recently troubleshooting an 07' TC alternator, and found one of the wires going back to the engine computer.

They designated the terminal as "M" on the alternator.

Here's what I can tell you about it...

12v pull down design, the engine computer sends 12v to the alternator and the alternator pulses it to ground.

The frequency I measured was 200Hz, and it's duty cycle was ~23%.

My question is this, does anyone know what this circuit is for? My first thoughts was load demand reports to the engine computer, but this frequency and duty cycle had no reaction to increased load demands on the electrical system.

My second thought was maybe this was some sort of fault detection circuit to the engine computer, but I had no fault codes (This alternator was bad btw.) I also looked for any data PID's referencing this circuit but found none (Verus 15.4 was the scan tool used.)

Any thoughts? I'll be uploading the troubleshooting vid on youtube tonight and I'll post a link here so you guys can see what I'm talking about.

Confusing -- why to they have to make so many different systems.
M is usually Monitor on Denso alternators which like you I normally have assumed is always alternator load feedback from the alternator to the PCM -- alternator pulls down from battery voltage but on the 105amp output ones I have see it is about 80 to 100 hz with a 50% to zero duty cycle depending on load. With a little 100 amp battery load tester on I can draw the duty cycle down to almost zero..

I wonder if what you are see is because the alternator has failed

That was my understanding as well. I'm definitely going to do some retesting after I get the new (O.E) unit installed for confirmation. This alternator being defective, it is highly likely that whatever sort of feedback signal it was modulating to the engine computer was also affected.

I will do some internet digging and see what comes to light.

Very general but this is useful stuff.

www.autoelectro.co.uk/sites/default/file...AERegulatorGuide.pdf

Great file! Definitely adding that one to my library. It seems to reinforce our load feedback hypothesis.

Here's the video I did on this one, I start focusing on the circuit in question around 16:16.

You're on the right track, it's a load monitor circuit for idle control. Reading into this signal is kinda weird. For example, this is a shot of the M circuit on a 2009 Camry with a failed alternator:



This is the after with a functioning alternator:



I've played with this circuit a bit on my Scion xA. Shorted it to ground with a test light, zero codes, charging voltage steady, and no idle change. :dry: They spent the money to integrate the circuit into the car, but don't seem to care much when it's not working correctly. :lol:

Andy.MacFadyen wrote: Very general but this is useful stuff.

www.autoelectro.co.uk/sites/default/file...AERegulatorGuide.pdf

This is good stuff. Adding it to the service info sticky.

Definitely a clear signal problem on that bad capture you have there. It is definitely a goofy design for sure. :S It would be interesting to sit down with the person who engineered it and see what exactly it's truly meant for.

SniperDan wrote: Here's the video I did on this one, I start focusing on the circuit in question around 16:16.

I liked the video, subscribed!
Thanks for sharing.

Also subscribed! Jelly of the underhood light.

This underhood light is killer, worth every penny. Noah OMG your signature :lol: