Jim Grant's Tech Tips
'99 Subaru, Fuel Trim Malfunction
I have 99 Subaru Forester and the check engine light has been coming
on. I had it checked on the computer and it comes up as a fuel trim malfunction.
Unfortunately it was not explained to me what is exactly wrong. Can you
trim is a dressy word for how much adjusting the computer has to do to
get the right amount of fuel to the engine. On todays vehicles this
information is reported as fuel trim. If the computer says, "hey
I ran out of adjustment" it turns the check engine light on. Fuel
trim problems come in two colors, either the engine is getting too much
fuel or not enough fuel. In either case, if the computer cant adjust
for the variations it gets upset and turns the check engine light on.
There are different computer codes for too much fuel and for not enough.
If the shop that is servicing your vehicle cannot explain that much to
you find another shop.