An additional thought to F Dryer's helpful ones...my own 2006 Matrix had intermittent ABS warning lights which turned out to be from failed solder connections in the dash ABS/clock module. Your situation is different, but the commonality might be a bad connector that looks good and works most of the time. This kind of problem can drive mechanics (and owners ) nuts because it might be hard to get things to misbehave while being scanned. In my case, I realized the issue and had my module refurbished without hours of fruitless troubleshooting by a mechanic. For you, any stored codes could be worth a lot. Good luck!