This page provides information in regards to the Circuit Opening Relay (COR) function, operation and wiring.
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The function of the COR is to switch power to the fuel pump when the engine is running or being started. Having power to the fuel pump only when the engine is being started or is running is a safety feature.
An example of an event in which the COR would disconnect power to the fuel pump would be an accident, where
In this scenario the COR will be controlled to turn the fuel pump off (as the engine is not running) and this will stop fuel from leaking at high pressure from the ruptured fuel line. This is a desirable (and legally required) safety feature that would not exist if the fuel pump was wired to come on directly with the ignition.
The COR is much like a normal relay, however it has two 'triggers', either of which can be used to turn the COR on and switch power to the fuel pump.
In all cases one of the triggers to turn the COR relay on is the ignition key being in the START position, this ensures that the fuel pump runs when attempting to start the engine is
In cars with a flap type Air Flow Meter (AFM) there is switch inside the AFM that is open when the engine is stopped, when the engine is running the movement of the AFM flap causes this switch to close and trigger the COR on.
When the engine is not running the AFM switch is open and the COR is off causing the fuel pump to be turned off.
In cars without flap type AFMs the engine ECU detects the engine speed (via the distributor or crank angle sensor, etc) and the engine ECU has a dedicated output pin (Usually labelled FC in Toyotas) that is connected to ground inside the engine ECU (via a transistor), to turn the COR on when the engine ECU determines that the engine is running.
When the engine ECU determines that the engine is not running the engine ECU FC output is turned off which causes the COR to turn off and the fuel pump to be turned off.
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