Need help with a ground issue

Nicholes Technician Reading, Pennsylvania Posted   Latest  
2018 International LT625 14.9L (ISX 15.0)

So I have been getting random datalink faults on for the front radar unit which is a wabco. It has proper power , ignition power, and can wires tested good. But when I ohmEd the ground from the negative pin to battery ground I had 100 ohms. But if I disconnect the battery ground it shows 0.03 ohms. I made sure all the wiring checked out good to the frame ground where the radar ground wire ends up going to. But does any one know why once I connect the battery up and ohm the ground wire front radar to battery ground I get resistance ?

Jürgen Owner
San Cristóbal de las Casas, Mexico
Jürgen Default

Ohm testing is valid only on not active, disconnected circuits. Your reading may well be result of an active circuit.

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Bruce Owner/Technician
New Brighton, Pennsylvania
Bruce Default

Ohm testing doesn't mean the circuit can carry a load. Voltage drop test does.

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Scott Owner
Moreno Valley, California
Scott Default

Hi Bruce, That's correct. I like saying checking resistance will prove a circuit is bad, but won't prove it's good.

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Dick Technical Support Specialist
Québec, Quebec
Dick Default

Suggest "loading" any disconnected circuit you wish to test with a load, (some use light bulbs) then measure the voltage drop across the load which should be exactly the same as source voltage. If lower, there is resistance in the circuit. Be sure the circuit can safely handle the load you use or The Load-Pro meter leads are another method of doing this. Electronic Specialties 180 LOADpro…

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JJ Technician
Quincy, Massachusetts
JJ Default

With everything plugged in, hooked up and powered on check for voltage on the ground wire at the radar unit. If everything is as it should be all voltage to the unit should be dropped by the unit. If there is resistance to ground somewhere in the circuit you'll get voltage remaining after the load, the load in this case being the radar unit. If there's 2 volts on the ground wire, after the load…

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default

What JJ said

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Eric Owner/Technician
Edgerton, Wisconsin
Eric Default

Nicholes, Are you familiar with voltage drop testing? Testing resistance of a circuit with an ohmmeter is not a reliable test method. Just like testing for voltage on a circuit using a volt meter is not a reliable test method. To verify the integrity of the circuit(s) you are concerned with you should apply a suitable load across the circuit, such as a headlight bulb, turn signal light bulb…

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Juan Technical Support Specialist
Lisle, Illinois
Juan Default

What Datalink faults are logging in relation to the Radar?

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Rick Owner/Technician
Saltillo, Texas
Rick Default

Sounds like a good job for the Maxiscope. Test the hot circuit for voltage differences at up to 4 different points starting at the battery a probe at the fuse and any connectors and ending at the unit being tested. Watch in real time all 4 points at once.

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