EagleTribune.com, North Andover, MA

October 21, 2012

Electrical gremlins tough to track down

Under The Hood Brad Bergholdt
The Eagle-Tribune

---- — Regarding the 1995 Buick Century battery drain issue referred to in your earlier column, I had a similar problem on a 1990 Buick Century, which has the same body design as the 1995.

It turned out it was the driver-side door switch. It had a prong on the door that contacted the body when the door closed. After 15 years and 160,000 miles of use, the prong wore a small divot into the door frame. During the daytime, the divot did not affect the switch operation. But during cold nights, the door would shrink, and the prong would move out, and the divot was sufficient enough to cause the switch to close and turn the dome light on during the night, thus draining the battery. I went crazy looking for a parasitic drain during the day and could not find one. I checked the car at 2 a.m., and found the dome light on. I fixed the problem by using epoxy to adhere a penny to the body frame where the prong touches it.

I couldn’t resist sharing this story, as it illustrates a fairly common problem, but with an odd twist. The writer’s persistence is also admirable. I don’t recall ever returning to the shop at 2 a.m. to check for an intermittent problem.

It turns out the 1995 Buick’s intermittent battery drain problem was a damaged/mispositioned trunk latch switch. About 4 out of 10 times the trunk was closed, the switch would remain closed, illuminating the trunk light. If the Buick was driven regularly, the drain on the battery wasn’t severe enough to cause a problem. But after a three-day weekend of non-use, it sometimes wouldn’t start. And her typical driving routine of short trips didn’t help, as there was limited time available for the charging system to refill the battery. Hats off to Evergreen Valley College automotive student Anthony Contreras for solving the problem quickly and with notable professionalism.

I remember another intermittent battery drain problem many years back that seemed to defy repair — it would apparently only occur when the vehicle was parked at the vehicle owner’s home. After several repair attempts, the cause finally surfaced when I gave the owner a ride home after dropping the car off for perhaps the fourth repair attempt. Her driveway was incredibly steep, and it was fooling the under-hood light mercury switch into thinking the hood was open.

Here’s a final odd intermittent problem — this time a fuse popping: It was a brand new Pontiac Firebird, which was towed in on five occasions with the engine computer fuse blown. A new fuse would be installed, and the car would run perfectly every time, and careful inspections turned up nothing.

I finally asked the owner at what point during a typical drive the engine would quit. He replied, “It doesn’t quit; it just won’t start.” Holy cow, I thought — this car blows fuses when parked. The only active computer circuit protected by that fuse when parked was a mass airflow sensor cleaning circuit — it would cycle for five seconds or so at shutoff. A chaffed wire was found behind the engine; it would rub against a seam on the firewall only when the car was parked on a diagonal slope, such as his driveway.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at under-the-hood@earthlink.net; he cannot make personal replies.