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Circuit Opening Relay

Page history last edited by wilbo666 2 months ago


 

Introduction

This page provides information in regards to the Circuit Opening Relay (COR) function, operation and wiring.

 

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Circuit Opening Relay Function

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

  • The driver is unconscious (and hence the ignition has been left on), and
  • The engine has stalled, and
  • The fuel line has been ruptured

 

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.

 

Circuit Opening Relay Operation

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.

 

Circuit Opening Relay Trigger 1

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

 

Circuit Opening Relay Trigger 2 - Flap Type Air Flow Meter Equipped Engines

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.

 

Circuit Opening Relay Trigger 2 - MAP Sensor & Non Flap Type Air Flow Meter Equipped Engines

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.

 

Circuit Opening Relay Wiring

 

Circuit Opening Relay Pinouts

Image from: http://www.justanswer.com/toyota/2chom-replace-circuit-opening-relay-1984-toyota-camry.html

 

 

 

 

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