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Re: APC failures - HELP Posted by Ari [Email] ![]() ![]() In Reply to: APC failures - HELP, RupertG, Wed, 13 Sep 2006 17:01:18 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Yes, the APC box and the BPC valve can kill each other in a weird suicide pact.
The valve (BPC in a '95, older cars used an APC solenoid) has three wires running to two coils. The APC controller electroncis control the valve position by putting pulses through the two coils. Equal pulses in each coil, and the valve is in the middle. Wider pulses on one side (and narrower on the other), and the valve moves one way. So the controller sends pulses. In the older APC system, the solenoid was on or off.
If one or both of the coils in the BPC valve is the wrong resistance or shorted, it will pull more current than rated. This will kill the transistor driver in the APC controller. If the APC controller screws up and instead of sending pulses to the BPC sends a straight voltage, it will overheat and kill the coils in the BPC valve, assuming the transistor doens't fail first.
So it is possible for a bad APC controller to damage the BPC. You then swap in good APC controllers, each damaged by the bad BPC. You swap out the bad BPC, but the transistor in the APC controller is already damaged; it fails, and sends lots of current into the good BPC.
However, the first thing I'd do is verify the wiring from the APC controller to the BPC. Make sure the wires go where they should, and more importantly, make sure they don't go where they shouldn't. No inadvertent grounds. If any of the wires to the BPC are worn and intermittently touch ground, it can damage both devices. Next, make sure the ground to the APC is in good shape.
You can test the coils of a BPC by measuring the resistance between pins 1-2, and 2-3. The resistance should be 3 ohms in each coil. I'm not sure of the tolerance - I've heard down to 2.7 ohms is possible. I'd be worried if it were below 2.0 ohms. Of course, most consumer volt-ohm meters aren't really accurate down that low. I'd say if it reads open or shorted, the BPC is bad.
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