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

Fuel Trim Cell

The scan tool displays the cell number. The fuel trim cell is dependent upon the engine speed and the Mass Air Flow (MAF) sensor readings. A plot of RPM vs. MAF is divided into 10 cells. The fuel trim cell indicates which cell is currently active.