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

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High Temperature Vacuum Signal Modulator


This unit is located at the rear of the engine compartment and is connected to the EGR vacuum signal hose. The modulator opens when the underhood air temperature reaches 115° F and causes a weakened vacuum signal to the EGR valve. As a result, the amount of exhaust gas being recirculated is decreased.