Coolant Level Sensor: Testing and Inspection

The low engine coolant level switch is used to detect when engine coolant in the coolant recovery reservoir drops below a certain level. The switch is a normally open switch located in the bottom of the coolant recovery reservoir that closes when the engine coolant in the reservoir is above a certain level. The switch is fed ignition voltage, which is used as a switch input to the Powertrain Control Module (PCM). The PCM can turn On the coolant level telltale (with low coolant level) by sending a message to the I/P cluster over the Class II link. When the coolant in the coolant recovery reservoir is full the coolant level input at the PCM should be high (ignition voltage). DTC P1620 sets when the engine has been running for a certain length of time and the coolant level input at the PCM is low.

DTC Parameters
Diagnostic Trouble Code (DTC) P1620 will set if the coolant level input at PCM is low (indicating low coolant level) when:
^ Condition exists for longer than 30 seconds
^ Engine is running
DTC P1620 diagnostic runs continuously with engine running.
DTC P1620 is a type D DTC.

Diagnostic Aids

To locate an intermittent problem, use Scan tool to monitor LOW COOLANT LEVEL. Wiggling wires while watching for a change from NO to YES may locate the area where an open or short to ground in the wiring could lie.
The Powertrain Control Module (PCM) will command the I/P cluster over the Class II link to turn the Coolant Level Telltale On when the engine is running and the coolant level input voltage goes low for 30 seconds. The telltale will remain On steady when this condition occurs.
Check level in coolant recovery reservoir and pressure test system if a leak is suspected.