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Power Side Switched Circuit- Normal Operation

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26 Feb 2019 07:13 #27377 by MOROSO321
I'm a little confused with activation of the transistor on and off. With the solenoid reading 0 and 0 with the transistor off, does that mean KOEO? Or when the transistor is on, does that mean KOEO OR KOER? Little clarification please. Thank you fellow techs.

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26 Feb 2019 11:03 - 27 Feb 2019 12:02 #27381 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Power Side Switched Circuit- Normal Operation
I could probably help you a lot more if you could give the chapter and page or video that is causing concern.

Before computers were used in cars power side switched used to be the way (almost all) circuits were switched.

A good example of power side switched would be an old fashioned light switch, no matter what position the key was in the light switch was continuously supplied with battery voltage through a fuse. Only when then switch was in the on postion could the electricity flow though the switch through the bulb to a local ground.

However some power side switched circuits were only supplied with battery power Key On Engine Off or Key On Engine Running . An example would be the brake light switch on most older cars. The brake light was supplied with power through a via the ignition switch, the though the brake light switch to the brake lights then to a local ground.

On pre 1980's cars ground side switched circuits were rare the main example would be the interior dome light which was continuously supplied with battery power but was only grounded when a door was opened.

It was the coming of computers and fuel injection that made ground switching more common.
Taking the fuel injectors and ignition circuits as an example they are supplied with an ignition switched battery voltage supply (usually from a main or auto shutdown relay) --- the supply will normally be in any Key On condition.

Injectors and coils are generally controlled by ground side switching. The injectors and coil packs are only switched (pulsed) on (grounded) for time periods controlled by the computer. This time on time is called the Injector Duration for an injector and the Dwell Time for a coil.
Although they are supplied with power at Key On the injectors and coil primary will only be pulsed to ground in time with crankshaft rotation Key On Engine Running.

Because the injectors and coils are only pulsed to ground for fixed time period (a few milliseconds ) they don't remain switched on so the injectors won't flood the engine and coils won't burn out.

"There's always a catch ---- Catch OBD2 ."


Last edit: 27 Feb 2019 12:02 by Andy.MacFadyen.
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02 Mar 2019 23:11 #27539 by ScannerDanner
Replied by ScannerDanner on topic Power Side Switched Circuit- Normal Operation
Feel free to ask these types of questions directly on the video it is related to okay? I make it a priority to answer them.

Don't be a parts changer!
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02 Mar 2019 23:15 #27540 by ScannerDanner
Replied by ScannerDanner on topic Power Side Switched Circuit- Normal Operation

MOROSO321 wrote: I'm a little confused with activation of the transistor on and off. With the solenoid reading 0 and 0 with the transistor off, does that mean KOEO? Or when the transistor is on, does that mean KOEO OR KOER? Little clarification please. Thank you fellow techs.

KOEO (key on engine off)
KOER (key on engine run)
Neither of these dictate whether or not the transistor is on or off. This will depend on the circuit and when it is supposed to operate.
When you're doing circuit testing on these, you can't do them with the key off which would be why you see these listed.
Make sense?

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19 Mar 2019 15:17 #27922 by MOROSO321
Replied by MOROSO321 on topic Power Side Switched Circuit- Normal Operation
yes it does sir. Thanks Paul.
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