CAT 3126E Fault Code: 43-02 PID: Flash Code 71 SPN: FMI: Key Switch Fault

Posted by PerDiezel Solutions on January 12, 2026

The Engine Control Module (ECM) detects that the keyswitch was cycled at least three times within one second.

This indicates that the battery circuit to the keyswitch has an intermittent condition or a low battery condition while the engine is running.

Note: This code can be generated by rapidly cycling the keyswitch. Some control modules on the vehicle require this action in order to prompt flash codes. If this occurs, clear the logged diagnostic codes in order to prevent future confusion or an incorrect diagnosis.

Note: This code can also be generated when there is an attempt to restart the engine immediately after a shutdown. The engine may not start if the engine speed did not reach zero rpm prior to the restart.

Probable Causes:

1) ECM Connection/Harness
2) If code 43-2 (Key switch fault) is logged, t/s that code instead
3) Low or excessive ECM power (from battery)
4) Wiring from battery to ECM
5) Keyswitch or keyswitch wiring
6) Aftermarket engine protection switch

CAT 3126E Fault Code: 105-11 PID: Flash Code 64 SPN: 1636 FMI: 16 Very High Intake Manifold Air Temperature

CAT 3126E Fault Code: 105-00 PID: Flash Code 64 SPN: 1636 FMI: 15 High Intake Manifold Air Temperature Warning

CAT 3126E Fault Code: 111-11 PID: Flash Code 62 SPN: 111 FMI: 18 Low Coolant Level Warning

CAT 3126E Fault Code: 111-01 PID: Flash Code 62 SPN: 111 FMI: 17 Low Coolant Level Warning

CAT 3126E Fault Code: 110-11 PID: Flash Code 61 SPN: 110 FMI: 16 High Coolant Temperature Warning

CAT 3126E Fault Code: 110-00 PID: Flash Code 61 SPN: 110 FMI: 15 High Coolant Temperature Warning

WARNING!