Operation CHARM: Car repair manuals for everyone.
Manuals through 2025 now available!

Our trusted friends have launched a new website named LEMON, which has newer manuals. It also contains all the CHARM manuals.

LEMON is the spiritual successor to CHARM, I recommend you try it!

Link: lemon-manuals.la or lemon-manuals.org.ua

(Some people have issue connecting. LEMON is investigating. For now, use Firefox or change your DNS server)

Or, hide this message: temporarily or permanently

Short Term FT Avg

Display shows percentage from -100% to 99%. The center position for the short term fuel trim is 0%. A percentage greater than 0% indicates that time is being added to the MCV pulse width, increasing the amount of fuel to the engine to compensate for a lean condition sensed by the average of both the oxygen sensors. A percentage less than 0% indicates time is being subtracted from the MCV pulse width reducing the amount of fuel to the engine to compensate for a rich condition sensed by the oxygen sensor. A value of 0% indicates no compensation is required to operate the engine at the desired 16.8 to 1 air/fuel ratio.