Aircon Relay which is controled by ECM supplies and cut electrical power to Aircon compressor. ECM activates or deactivates Aircon Relay based on inputted signal such as aircon switch siganl and Aircon switch signal.

As controlling Aircon Relay, ECM 1)turns OFF aircon compressor at rapid acceleration to retain suffiecient capacity for acceleration, 2)actively performs idle-up function to cope with the change of engine load which happens at aircom compressor operation.

P0646 is set when ‘0A’ is detected in Aircon relay control circuit for more than 1 sec.. This code is due to open or short to ground in Aircon relay control circuit or internal open in relay component.