For 1990-2009 cars

### Low Coolant Switch Circuit

### Circuit Description

The low engine coolant level switch is used to detect when engine coolant in the coolant surge tank drops below a certain level. The switch is a normally open switch located in the bottom of the coolant surge tank 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 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 surge tank 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.

### Conditions for Setting the DTC

DTC P1620 will set if the coolant level input at the PCM is low, indicating low coolant level, when:

• | The condition exists for longer than 30 seconds.

• | The engine is running.

DTC P1620 diagnostic runs continuously with the engine running.

DTC P1620 is a type D DTC.

### Diagnostic Aids

To locate an intermittent problem, use the 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 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 the level in the coolant surge tank and pressure test system if a leak is suspected.