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In the trucking industry, technicians tend to take shortcuts when working on electrical problems. Instead of tracking down the source of the problem, many mechanics just start making assumptions and changing parts. It doesn’t matter whether the technician doesn’t understand how to diagnose an electrical problem or is just too lazy to do it – you are the one who’s buying the parts, so their assumptions end up costing you. These guys will typically tell you that the ECM, a sensor, a wiring harness or even an injector is faulty without bothering to test the part and verify that it has actually failed. These parts are expensive, and the technician telling you to replace these parts isn’t buying them – you are – so beware of any technician that doesn’t have a well-used multi meter sitting in his toolbox.




Electrical problems are not always easy to find – especially if they are intermittent. Some problems only show symptoms under a load, at a specific rpm or when it’s cold outside. Most intermittent electrical problems come

and go with no observable reason at all. Thankfully, if your ECM does produce a “check engine light” it will log which circuit produced the problem, then you can find it. If a wire is severed or a sensor fails, the ECM only knows it’s getting zero volts back from the sensor. You may just have a dirty, loose, corroded, wet or filled with oil connector. To find out, you have to ohm out the circuit to find the break with a good old-fashioned

multi meter. Diagnostic software won’t do this for you – a multi meter is the only way to be sure.