digital logic probe

[dewey]

I don't know anything about electronics, but I was wondering about using a digital logic probe to test a computor ground on an automotive application?

On my vehicle, I used a 9 volt power source for the probe, touched the probe ground and pointer to the frame at different places, the lower case lite came on and the buzzer. Did the lite come on because of continuity, or some other reason? Would it be safe to check an automotive computor ground that way? thanks

 

[jkmadsci]

a logic probe is not a good device to check for ground. One way to check
ground is to measure voltage accross the battery with a voltmeter and compare this reading to the voltage at the computer. The voltage at the computer should be within apx .4 volts of battery voltage. if you dont have good voltage at the computer than you can check hot with respect to a good ground and also check ground with respect to a good hot.
Its kind of hard to explain, but you can use the battery terminals as a
as a known ground and reference voltage.

 

[dewey]

Thanks for the reply. In the past, I have checked a sensor ground, that according to the wiring diagram, went to the automotive computor. I used an led with a resistor, came off the positive battery post, touched the ground wire, and this was a constant ground, the lite came on, so I guess the ground was ok. I just wondered about using the logic probe.

I wondered if the probe put out any voltage, I checked it with a volt meter, couldn't find any. With the probe leads grounded, the lower case lite came on. The lite came on because both leads were grounded completing the circuit for the lite? thanks