Does anyone know why the AFM return signal for an 88 s4 TII would never show voltage? ECU has afm code but i have tried two refurb afms and checked that twre is continuity from the afm plug to the ecu. Does the ecu create that signal or te afm? Imam getting the righ voltage and resistance everywhere else on that circuit.

If anyone cn confirm which device sends te signal that will help me finish troubleshooting. Thanks

 

Ok so I may have chased down the or atleast an issue. I have ground measurable ground continuity between the brown and white wire that feeds the afm, tps, and pressure sensor. I also have 5V with the key on to the same wires. I assume this means i have a short somewhere.

 

Which wire/pin are you talking about? 2E (Green/Blue) is an input signal and pin 2J (Green/Orange) is also an input signal. Does pin 2A (output signal which powers the sensor) have 5 volts w/key to on and sensor plugged in? And refurbished units are known to be a waste of money as a used one would be a better route to take.

 

So 2E never has power at all. Not with the key on and flapper door open/moving.

2J does have power with the Ignition on.

2A also has power with Ignition on and sensor plugged in. 2A is the brown and white wire that I was talking about showing some ground continuity. Is that ever normal? It does not drop to zero on the DVM like a true solid connection but it does show .6 when set on the 2K ohm setting on my DVM... I am still learning. To me that would indicate there may be a short maybe in 2A somewhere?

Once I have this figured out I am most likely going to return the AFMs and just get one off the forum as you mentioned they do not seem worth the money.

Thanks

 

Pin 2A should always have 5 volts w/key to on. If you unplug the sensor and the voltage returns to 5 volts but drops w/the sensor connected then the sensor is bad. There is no need to be checking for ohms on a single wire unless you are looking for a wire that is grounded out and no need to be looking for continuity between pins either. Pin 2E should have about 4 volts w/key to on. 2J voltage is based on air temperatures and would read 2 to 3 volts w/key to on at 68 degrees.

 

That is what I am saying. There is a reading between pin 2A and the body of the car on the ohm meter. Would that most likely mean it is grounded somewhere?

All the other readings match what you described except 2E. 2E never has voltage ever.

 

You don't take ohm readings from the ECU. If you want to see if the wire to pin 2A is grounded then you unplug the wire from both ends and test it that way. If pin 2A reads 5 volts as it should w/the sensor plugged in then there cannot be a ground issue or it would not indicate 5 volts.