Experienced service personnel usually have favorite firsthand accounts of how carelessness and/or slovenliness cost a customer a pile of money.
What's more, those in the snow-and-salt belt tell tales of unexpected damage done by plain old corrosion. Here's a worthwhile example that fits both categories.
A sharp technician I have worked with for many years encountered a 1996 Honda Civic that displayed an array of puzzling symptoms. The customer's main complaint was an unstable, unpredictable idle quality. The engine behaved, he said, as if there was a ghost in its works.
One moment the engine would idle smoothly and normally. A heartbeat later, it seemed, it would idle very roughly. The next moment, it would idle much too fast. The engine compounded the tech's frustration by refusing to repeat its symptoms in any kind of predictable way.
The list of trouble codes the engine control module (ECM) produced was strange, too. For example, it coughed up two different failure codes for the idle control system alone. It gave up a code indicating an abnormally high manifold absolute pressure (MAP) sensor signal and a code for an automatic transmission-related failure.
When the tech examined the engine control system's basic data on a scan tool, it was equally bizarre. For example, the MAP sensor signal—normally a very stable, predictable signal—was extremely erratic and unstable. Likewise, the system was flitting back and forth between a relatively normal and then a very rich air/fuel ratio.
The unpredictability of the readings prompted the tech to examine the wiring harness connections at the ECM (inside the right kick panel, a few inches above the car's floor). This was the dead of winter; a large piece of ice was frozen onto the right-side floor, right below the ECM. A lot of the car's carpeting was soaking wet. Closer inspection revealed the worst corrosion he had ever seen on an ECM and its wiring harness. The condition was so severe that he ended up replacing both the ECM and its harness.
There was no evidence that water had been leaking down from the windshield area. Rather, it appeared that large quantities of snow and salt were tracked inside the car over a long period of time. This corrosive mix would then eventually melt and evaporate inside the car, attacking the vulnerable ECM terminals nearby.
One lesson here is that you shouldn't overlook obvious clues such as the ice chunk and wet carpeting during your diagnostic process. The other lesson is that slovenliness can be more expensive than some motorists realize.
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