12 April, 2025CAT 3406E (Prefix 5DS or 1LW) Fault Code: 66 PID: 40 SPN: FMI: 6 Auxiliary Output #02 current high Conditions Which Generate This Code: The ECM detects the following conditions: •There is a low current condition (open circuit) in auxiliary output 02. Probable Causes: 1) ECM Connector/harness2) Shift solenoid failure3) Shift solenoid relay4) Wiring between shift solenoid and ECM5) Gear ratios are programmed incorrectly in the ECM 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.