The Warning Light That Comes and Goes: Log the Conditions Before the Light Stays On

An intermittent warning light is hard to describe from memory. It appears, it goes out, and by the time the car is in front of anyone it is dark again. A written log of each appearance gives the technician, and you, something to work from.

Why a Log Works Better Than Memory

Each appearance has conditions: outside temperature, speed, the road surface, the load, how long the engine had been running, and whether the car was on a hill or in stop-and-go traffic. These details fade quickly. Written on the day, they show which conditions repeat.

What to Write Down Each Time

Record the day and time, the light's name or symbol as shown on the panel, its colour, and whether it stayed on or flashed. Note the outside temperature, the odometer reading, the speed when it appeared, and what the car was doing. Note whether any other light, message, or sound came with it, and whether the light went out on its own or after the engine was switched off and on again. Keep each entry short and use the same format every time.

Read the Manual's Light Table First

The owner's manual states what each light means and what it asks the driver to do. Read that entry before you rely on the log, and follow the manual's instruction whenever a light is on. A log is a record for a visit, not a reason to keep driving a car whose manual tells you to stop.

Keep the Log With the Car

Keep the log in the glove box or with the service papers, not only on a phone that may be replaced. Bring it to every visit. Note whether a service visit reproduced the light and what the shop checked or changed. A log that includes the shop's findings is more useful at the next visit than one that lists symptoms alone.

Check the Federal Record Too

Before you assume the light points to one fault, look at the model year's entries on the model-year record for recall notices and complaints that mention a warning light. Compare any entry with your own log before drawing a conclusion. A complaint describes what one owner reported, and the federal count beside it is a count of those reports.