Looking at a '99 V6 with 71,000 miles.
Yellow check engine light stays on constantly.
Owner has repair receipt for oxy sensor replaced 13 months ago at 52,000 miles and apparently Ford dealership looked at this recently and did something to get the light to go out, but, it has come back on again.
Any ideas as to possible causes and repair cost?
Does the 2.5 V6 with timing chain (I believe) require replacement of the timing chain and if so, at what mileage and again, approximate cost?