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)

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Highway Fuel Mode (Semi-"Closed Loop")

Highway Fuel Mode (Semi-"Closed Loop")
This mode comes into operation at highway speeds and its purpose is to improve fuel economy. For the control module to operate in this mode, it first must sense the correct engine coolant temperature, ignition control, canister purge activity and constant engine speed. During semi-"Closed-Loop" operation, there will be very little long term fuel trim (formerly known as "Block Learn") and short term fuel trim (formerly known as "Integrator"), and the heated oxygen sensor values will read below 100 millivolts.