Thread: Mysteries Of Discovery 4 Electrics

I had no end of trouble when my alternator was replaced. Straight swap in my case to a new one, but the error remained. Not immediately, only appeared after a 20min drive or so.

Solution in the end was a complete reset of the car - back to ‘new born’ state. Elements of the egr remap had to be reinstalled, to give an idea of the level of ‘wiping’ that went in with the ecu.

All good since…

Originally Posted by veebs

I had no end of trouble when my alternator was replaced. Straight swap in my case to a new one, but the error remained. Not immediately, only appeared after a 20min drive or so.

Solution in the end was a complete reset of the car - back to ‘new born’ state. Elements of the egr remap had to be reinstalled, to give an idea of the level of ‘wiping’ that went in with the ecu.

All good since…

Funny you say this. When my crankshaft position sensor was replaced, they couldn’t get it to go again. They too had to flash the PCM to get it to run again. Hard to understand what’s going on, but maybe some state gets retained that causes issues.

Originally Posted by Eric SDV6SE

Is simply replacing this wire completely an option or are the gauge changes a requirement (fusible links were mentioned)

Maybe someone who is totally familiar with the communication protocol used on this link can explain the reasoning behind this. It is beyond my level of comprehension despite using protocols prevalent in data communication applications for most of my working life.

Originally Posted by Gravy

Maybe someone who is totally familiar with the communication protocol used on this link can explain the reasoning behind this. It is beyond my level of comprehension despite using protocols prevalent in data communication applications for most of my working life.

There is no communication on that wire. It's the positive supply for the BMS. I can't explain why they'd do it that way.

The LIN wire goes from the BMS to the BCM. LIN is a simple open-drain, single wire, bi-directional serial protocol. The devices (one or more) have a pull-up resistor that pulls the LIN wire to 12V, and they assert the bus by pulling it low (transistor or MOSFET usually). When they relinquish the bus, the combined pull up resistance pulls it high again with the time constant of the combined resistance and the capacitance of the bus. It's simple and robust, but as it relies on a passive pull-up it's not particularly high speed.

Originally Posted by BradC

There is no communication on that wire. It's the positive supply for the BMS. I can't explain why they'd do it that way.

The LIN wire goes from the BMS to the BCM. LIN is a simple open-drain, single wire, bi-directional serial protocol. The devices (one or more) have a pull-up resistor that pulls the LIN wire to 12V, and they assert the bus by pulling it low (transistor or MOSFET usually). When they relinquish the bus, the combined pull up resistance pulls it high again with the time constant of the combined resistance and the capacitance of the bus. It's simple and robust, but as it relies on a passive pull-up it's not particularly high speed.

No idea what you said, but sounds like a good explanation.

Originally Posted by Eric SDV6SE

No idea what you said, but sounds like a good explanation.

Are you old enough to remember the leather ropes that ran the length of the bus? You pull down on the rope to ring the bell and let the driver you want to get off.

It's a lot like that. The rope has a spring (the resistors that pull the bus up to +12V). Any device that wants to signal pulls the bus down. It doesn't matter if one or 4 do it, the result is the same. The bell rings once.

Now picture it as the driver calls out the seat numbers in turn. Seat 1, seat 2 and so on. When he gets to a seat number that wants to get off they pull the rope. In a LIN scenario there is one master and one or more slaves. The master calls out the slave addresses in order and if a slave has something to say it pulls the rope.

Now we complicate it in that the master talks to the slaves by pulling the same rope. It's still just a rope on a spring, and there are only 2 states. Pulled and not-pulled. The LIN bus is the same. It's either pulled up to +12V or down near ground and the threshold is half way. Is it above 6V or below 6V.

Originally Posted by BradC

Are you old enough to remember the leather ropes that ran the length of the bus? You pull down on the rope to ring the bell and let the driver you want to get off.

It's a lot like that. The rope has a spring (the resistors that pull the bus up to +12V). Any device that wants to signal pulls the bus down. It doesn't matter if one or 4 do it, the result is the same. The bell rings once.

Now picture it as the driver calls out the seat numbers in turn. Seat 1, seat 2 and so on. When he gets to a seat number that wants to get off they pull the rope. In a LIN scenario there is one master and one or more slaves. The master calls out the slave addresses in order and if a slave has something to say it pulls the rope.

Now we complicate it in that the master talks to the slaves by pulling the same rope. It's still just a rope on a spring, and there are only 2 states. Pulled and not-pulled. The LIN bus is the same. It's either pulled up to +12V or down near ground and the threshold is half way. Is it above 6V or below 6V.

Cheers for the "real world" clarification Brad.

does anyone know where i can get a replace connector for the back of the alternator i think it is the LIN plug i snapped the wire right at the ceonnector and can't solder it. it is a denso alternator that i have purchased. i have spent over 2 hours looking for the part but can find it any where.