DTC P1620: Low Coolant Switch Circuit: Description

Low engine coolant level switch is used to detect when engine coolant in coolant surge tank is less than a certain level. Switch is a normally open switch located in bottom of coolant surge tank that closes when engine coolant in reservoir is greater than a certain level. Switch is fed ignition voltage, which is used as a switch input to PCM. PCM can turn on coolant level telltale (with low coolant level) by sending a message to instrument panel over Class II link. When coolant in coolant surge tank is full, coolant level input at PCM should be high (ignition voltage). DTC sets when engine has been running for a certain length of time and coolant level input at PCM is low.