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ECM Testing and VATS

94masterroader

New member
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Buick Ownership
Roadmaster wagon
Trying to determine why my car does not crank. My ignition resistor is fine. However, if the body control module is bad, the ECM will not get the pulse it is looking for at pin A25 (fuel enable). Also, the relay to turn on the starter (under the dash) will not turn on. I see all the videos claiming it is the resistor on the key. Maybe in some cases but definitely not all. The signal to pin A25 is a square wave. It pulses a ground signal to the pin which I believe is high (+5v) otherwise. The frequency should be either 30hz or 50hz. It depends on the car and year. I was not really able to verify what it should be. My signal was not there. I checked my resistance. It was fine. I by-passed the relay coil. After doing that the starter would engage. The engine would crank and try to start. I checked the signal at pin A25. Nothing. I built a small circuit to produce 50hz with a 50% duty cycle. I connected the circuit. The ECM just grounds the pulse out. At this point I am not sure if my ECM is bad also. I used the Factory service manual to determine the body control module (VATS) is bad. How can I test my ECM or am I able to use a junk yard ECM to at least get my car started? I know it will not run correctly with a junkyard ECM, but will it start? Anyone have info on the fuel enable pulse frequency at pin A25?
 
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