Five years ago, I began seeing a very small number of General Motors products come through the door with a variety of trouble codes indicating a "circuit failure" in the intake air temperature (IAT) sensors, mass air flow (MAF) sensors, throttle position (TP) sensors and idle air control (IAC) systems. In all cases, these failures were intermittent or random failures that were difficult to duplicate, which required one or more return visits before I could pinpoint the problem. Most had circuit failure codes and one had no codes at all.

What was the problem? After much trial and error and a great amount of frustration on my part, I found that all of these failures were caused by a wire losing continuity inside the insulation or at a terminal evidently crimped over the insulation on the wire. Not that this is a common failure; as a matter of fact, it's relatively rare. In 40 years of repairing motor vehicles, I had previously encountered this condition only once or twice.

The History of Wiring
For the most part, the electrical wiring found in most automotive systems is very dependable. In the late 1980s, a few Ford and Chrysler products had a problem with the insulation peeling off the wire's copper core when exposed to petroleum-based fluids and vapors. Some of the old '80s Ford products also had wiring splices within their wiring harnesses that would separate when the wiring harness was stressed during an engine ...