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Old 02-21-2006, 03:51 PM
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EEC Power Diode

In the process of trouble-shooting my electrical system (another story), I came across this power diode in the engine compartment fuse box. It appears to be in the circuit that activates the PCM power relay (in the same fuse box). I've always tested diodes by checking the continuity twice, reversing the leads each time. If it works one way but not the other, diode's good. My diode, however, shows overload both ways (that would be infinity on an analog meter).

But, my meter only measures up to a thousand ohms, so anything over that would probably also show up as "OL". How can I tell if this diode is any good?
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Old 02-21-2006, 03:59 PM
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Don't know an easy way unless you have another meter. That cheaper meter should be able to check the diode, unless it has only one 1.5v battery in it, and the battery was low. Most diodes need about .7 volts to start conducting.
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Old 02-21-2006, 06:04 PM
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If you turn your key on and PCM Power Relay clicks (energizes) the Diode is good. Its to stop the power to PCM if you hook up jumper cables wrong, at least that is what I think it is for.

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Old 02-21-2006, 06:04 PM
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If you turn your key on and if the PCM Power Relay clicks (energizes) the Diode is good. Its to stop the power to PCM if you hook up jumper cables wrong, at least that is what I think it is for.

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Old 02-22-2006, 10:17 AM
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The meter must have a diode test function if it's a digital in order to test diodes and transistors.

The cheapies aren't able to source enough voltage at constant current to forward bias the PN junction.

The diode appears to be there to keep the PCM POWER relay coil from experiencing back EMF from the ignition coil which might cause it to chatter. It will also keep the PCM from receiving power in the event that battery power is reversed.

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Old 02-22-2006, 11:47 AM
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Thanks. Diode is good, and my journey continues. It really bugs me to run across something like that and not know what it's there for or what it does, so I wanted to put my mind to rest.
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