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Jim Grant's Tech Tips
A Lot-a Warning Lights
Q:
My service engine light was on for a week, I thought it was because I did not put the gas cap on properly. I read in the manual it should take about 3 cycles for the light to go out. After a week the light was still on, so I took it to the dealership, they did a diagnostic test and said the 02 sensor skipped. They reset the computer so that the engine light went out. A week later, the engine light is back on, afterwards the battery light came on and shortly after that the ABS indicator light came on. As I was driving home the radio went out and the lights inside the car started to dim. After shutting the car off, I tried to restart and it wouldn’t. The headlights did come on. I noticed as I put the security alarm on the car, it sounded weak. Could you please give me an indication of what may be wrong with this vehicle, so that I can trust, when I take it to the shop, I have some sort of idea what is going on with the vehicle.
A:
It’s very unlikely that the check engine light from the week before is related to the problem you’re having now. From your description I would guess that the charging system on your vehicle has failed. The first indicator was the battery warning light. The job of the charging system is to provide electrical power for the vehicle’s needs and replenish the battery. The main job of the battery is to store electrical power for starting the engine. After the engine is running the charging system takes over. In the event of a charging system failure the vehicle’s electrical demands are supplied by the battery. On today’s vehicles it doesn’t take long for the battery to drain to the point that other computer systems take notice. When they see that the power supply to them is too low to operate correctly the other computers start complaining which would explain your ABS warning light. As the battery gets lower the radio will drop out, which is just about the time the engine computer will start thinking about throwing in the towel. At this point the battery has about enough power to light some lights but wouldn’t even think about cranking the engine over. The fix for your vehicle is likely a new alternator. Once you’re up and going the check engine light may come back on because of the O2 sensor problem, but that won’t kill the battery.
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