29 March, 2025CAT 3126B Fault Code: 111-02 PID: Flash Code 12 SPN: FMI: Coolant Level signal invalid The ECM detects the following conditions: •The coolant level sensor is sending an invalid signal for more than ten seconds.•The “Coolant Level Sensor” parameter is programmed to “Yes”. Probable Causes: 1) ECM Connection/Harness2) Coolant sensor failure3) Coolant sensor harness failure4) ECM Failure Share on Facebook Opens in a new window. Tweet on Twitter Opens in a new window. Pin on Pinterest Opens in a new window. Back to blog Leave a comment Name * Email * Comment * Please note, comments need to be approved before they are published.