Cummins ISB CM550 (1990-94) Fault Code: 422 PID: 111 SPN: 111 FMI: 2 Colant Level Sensor Circuit Coolant Level Sensor Circuit

Circuit Description
The coolant level sensor monitors the coolant level within the coolant system and passes
information to the engine control module (ECM) through the engine harness. This sensor is
very complex. Do not use a multimeter to check the coolant level sensor. If the radiator coolant
level drops below a certain level, a progressive power derate with increasing time after alert
will occur.

Component Location
The coolant level sensor is located in the radiator top tank or surge tank.

Shop Talk
This is an original equipment manufacturer (OEM)-supplied component and will vary in sensor
location.
1) If a shorting plug is used in the coolant level circuit, verify that it is wired correctly.
2) Inspect the wiring harness between the Weather-Pack four-way connector and the
coolant level sensor for damage.
3) Make sure the coolant level sensor is located in the middle of the tank rather than off to
one side where the coolant level can change when the vehicle makes a turn.
4) Sterling trucks utilize ECM pin A22 for coolant level sensing through a 2 pin sensor.