The low coolant lamp in diesel vehicles illuminates in order to indicate that the radiator has a low coolant level. Battery voltage is available to the engine coolant level indicator module through CKT 39 (PNK) from GAUGES fuse 4 when the ignition switch is in the RUN position or in the START position. The module has ground at G201 through CKT 150 (BLK). The module senses a variable resistance to ground at the low engine coolant level indicator sensor through CKT 1478 (LT GRN). The sensor has a resistance of 50,000 ohms or more when the coolant level is low. The resistance decreases to about 10,000 ohms when the radiator is full. The sensor has ground at G109 through CKT 151 (BLK/WHT). The low coolant lamp lights when the resistance to ground is approximately 50,000 ohms or more.