Erratic problem a puzzler
Q uestion: Brad, we have a 2005 Ford Focus station wagon. About two years ago, some of the warning lights would flash on and off for a fraction of a second, every two weeks or so. It then started doing it to all of the warning lights. One day, we went into a store. When we came out, the door would not unlock. Everything was dead, and the car would not turn over. I checked the battery connections; they were clean and tight. I figured I had an open circuit in the battery. After about 40 minutes, the radio started to play and the car started like normal. I got a new battery but after a few months, it acted up again.
I took it to a dealer, and they could not find anything wrong, except a ground that had a little corrosion on it. There were no faults on the computer, so they flashed the computer anyway. It was OK for several months.
Then on Oct. 22, when I was going to get gas, it started again. The engine would cut out for a fraction of a second, warning lights would flash, and the radio stations would change. I filled up the tank and got in the car, and everything was completely dead. I checked the battery connections, and they were all OK. I got back in the car and everything was normal.
I took the car to the Ford dealer. Again they checked it out, drove it around, checked the computer, no faults. Since they could not see the problem, they could not correct it. What could cause this?
Answer: Daniel, your situation has to be very frustrating. Your Focus clearly has an intermittent open/high resistance electrical fault near the trunk of the tree — battery, terminal connections, cables, and battery junction box. You can aid the diagnostic process or possibly solve the issue yourself with some simple tests. Start by obtaining an inexpensive digital multimeter, such as Sears Craftsman DMM model MN16A, which you can find for less than $30. Next, be sure both battery terminals and battery posts are shiny-clean and tight.
Next time the Focus acts up, immediately check for available voltage of about 12.6 volts across the battery terminals. I'm guessing this will be good — if not, it's a second devil-battery. Then touch any of the fuses within the battery junction box, in the left rear corner of engine compartment, with the red lead. Your black meter lead is connected to the negative battery terminal. Again, check for available voltage. If this test fails, the fault is between the battery's positive terminal and the junction box.
If this tests OK, turn on the headlights and touch the red meter lead to the battery negative terminal post, and the black lead to shiny engine metal. If the meter reads a value that's not very close to zero, the ground connection between the battery and powertrain/body is faulty.
These tests can be tried when the car is behaving, as you wiggle cables and connections — look closely for an abrupt downward or upward change in readings. This will be easy to fix once the measurements suggest the path.
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at firstname.lastname@example.org.