does a 99-04 pcm switch ground or power?
#1
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on...
fans
hi and low
and the fuel pump?
For some reason....I want to say they switch ground on the fans and B+ on the fp.....set me straight please so I dont have to probe wires.
fans
hi and low
and the fuel pump?
For some reason....I want to say they switch ground on the fans and B+ on the fp.....set me straight please so I dont have to probe wires.
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^^^^^^
WRONG WRONG
You are straight and correct
WRONG WRONG
You are straight and correct
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Lower current devices such as fuel injectors are switched directly by the PCM. A relay is used to switch higher current devices. For high-current devices the relay coil, which itself requires low current, is directly connected to the PCM and high current flows to the device through the relay's contacts. In ALL CASES the PCM switches the ground leg of the circuit. If the circuit includes a relay, the relay contacts switch the "B+" side of the circuit. The fuel pump and both fan motors are controlled through relays. I hope I haven't increased the confusion.
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#8
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Lower current devices such as fuel injectors are switched directly by the PCM. A relay is used to switch higher current devices. For high-current devices the relay coil, which itself requires low current, is directly connected to the PCM and high current flows to the device through the relay's contacts. In ALL CASES the PCM switches the ground leg of the circuit. If the circuit includes a relay, the relay contacts switch the "B+" side of the circuit. The fuel pump and both fan motors are controlled through relays. I hope I haven't increased the confusion.
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The schematic shows 2xLS1 is correct - I was wrong. My only excuse is that I'm an electrical engineer who specialized in microprocessor control systems.
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Last edited by Gary Z; 03-24-2012 at 05:25 PM.
#11
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What specific 04 Silverado are you refering to and I'll look it up because I've not seen one controled by a ground. I thought it was GM engineering's way of preventing a run a way pump if the circuit gets shorted to ground.
Here is a 2004 Chevy Truck Silverado 1500 2WD V8-5.3L VIN T schematic.
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Up until aprox.03 GM used almost exclusively ground side switching on their fuel pump circuits.I dont know why they switched to + switching but the fact clearly indicates this change. Long story short you must consult the proper wiring schematics for your project. It is simple enough to check this circuit with a multimeter by probing the wire in question with one lead and by probing either the positive or negative with the opposite lead while an assistant operates the key. So in conclusion both are correct.
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Flame,If you check some older wiring diagrams you will find that all of these systems used a computer controlled ground to activate the relay for the fuel pump. Look at a 2002 Silverado vinT for a good example of this. I work as a GM technician specializing in electrical and computer diagnostics.I have been doing this for 20+ years and have seen many changes come along. I still say consult the proper diagram to confirm circuit operation.
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Flame,If you check some older wiring diagrams you will find that all of these systems used a computer controlled ground to activate the relay for the fuel pump. Look at a 2002 Silverado vinT for a good example of this. I work as a GM technician specializing in electrical and computer diagnostics.I have been doing this for 20+ years and have seen many changes come along. I still say consult the proper diagram to confirm circuit operation.
2002 Chevrolet C1500 VIN T
#16
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Flame,If you check some older wiring diagrams you will find that all of these systems used a computer controlled ground to activate the relay for the fuel pump. Look at a 2002 Silverado vinT for a good example of this. I work as a GM technician specializing in electrical and computer diagnostics.I have been doing this for 20+ years and have seen many changes come along. I still say consult the proper diagram to confirm circuit operation.