Easy Circuit Testing?

Just trying to make sure that I am understanding correctly, so if it am figuring out a problem with a circuit such as a thermistor, trying to figure out if the circuit wiring or the sensor is the problem, is it ok to ground the signal wire with a test light, or jump it with the ground wire? Are there cases when this is not ok? I know you would not want to ground a 5v ref power wire; because that would drop the whole circuit right? But could I jump the 5v ref power with the sensor signal? I just don't want to smoke a computer

In the case of thermistors, you can pretty confidently ground the signal wire with no risk to the PCM. NTC thermistors are, by design, progressive shorts to ground.

I can't think of a situation that you wouldn't want to do this kind of testing? Not right now, anyway. :silly:

AJeep18 wrote: is it ok to ground the signal wire with a test light, or jump it with the ground wire?

Yes. Thermistor Circuits have and internal resistor that protects them from shorting. The Sensor, itself, shorts the Bias voltage to ground, (or, power) at varying degrees of resistance, changing with temperature.

Are there cases when this is not ok?

Not to my knowledge. Someone will chime in, if I am wrong.

I know you would not want to ground a 5v ref power wire; because that would drop the whole circuit right?

Right. Do not do that.

But could I jump the 5v ref power with the sensor signal?

Yes, you can do that but, remember that the thermistor signal circuit may have a 5 volt bias.

Tyler wins, by a nose!

Ok thanks! I was just using a thermistor as an example because I have dealt with a couple lately. The same thing would apply to pressure sensors as well right? A three wire would have power ground and signal and one could jump the signal with one of the other two and check the circuit that way right?

AJeep18 wrote: The same thing would apply to pressure sensors as well right? A three wire would have power ground and signal and one could jump the signal with one of the other two and check the circuit that way right?

Yes. The scan data should go from one extreme, to the other.