Does anyone know where the reference voltage for pin 2A on the ECU originates? j9fd3s ? Perhaps.

Please, no wise cracks about how it originates at the battery.

I mean what item in the ECU puts the reference voltage on pin 2A.

 

The reference voltage comes FROM the ECU and is generated by a voltage regulator inside the ECU. It sends 5 volts out to sensors like the MAP sensor, TPS, and air flow meter which all operate between 0 to 5 volts.

 

Uh huh. That's why I wrote the last sentence in the first post. j9fd3s has the information, I believe, of the particular item that outputs the reference voltage and hopefully the path. I truly, truly, did not just fall off the turnip truck.

 

Ooooops! Sorry about that, I should have read your post more carefully.

I suppose the part number of the ECU would be helpful as there may be a different path / VR between model years.

Good luck on your repairs!

 

An N332 would be fine but a N326 would get me there, I believe. Either or. I'm fairly sure its the regulator attached to the right side of the ECU that's using the ECU case as a heatsink.

 

I've got plenty of pics of my S5 TII ECU, but it's an N370 series. I see a similar device on mine too:

 

Yo. It's the item that's green and located on the bottom of the picture, to the left side. This particular ECU that I aquired came from a car that had a boost sensor problem. I think it's possible that 12v got put on the ref voltage line back to the ECU on pin 2A. That results in the reference voltage not being there any more.

What really hurts is that it killed the ability of the car to start. I think the same ref voltage is used for the CAS, therefore no sparky, no varoom, varoom.

It's just a little project I revisit once and a while to see if I can get it a goin again (the ecu, not the car).

 

I'm not surprised at the no-start, but it won't be because of the CAS. The CAS is an unpowered device that uses two mag sensors which generate an AC waveform in the presence of gear teeth.

If you've got no Vref then you've got no TPS, no pressure sensor, no ATP sensor (baro), and no variable resistor for idle mixture.

If that's the only probelm you could unlock and remove pin 2A from the connector and connect an external supply to it. Just be sure to get the ground for the external supply from 2C (analog ground).

 

Yes/no. I think whatever is killing the reference voltage, is killing the circuit/device, that pulses a on/off +/- 5v to the coils which is the determined by the output of the cas to the ECU. No output to the coils, no worky.