CAT 3406E (Prefix 1MM or 2WS) Fault Code: 34 PID: SPN: 190 FMI: 12 Primary Engine Speed loss of signal

The ECM detects the following conditions:

•The signal for the secondary engine speed/timing sensor is intermittent or lost.

The engine uses two engine speed/timing sensors. One sensor picks up the camshaft gear and the other sensor picks up the crankshaft gear. Both of the engine speed/timing sensors detect the reference for engine speed and timing from a unique pattern on the gear. The ECM counts the time between pulses that is created by the sensor as the gear rotates in order to determine rpm.

Under normal operation, the secondary engine speed/timing sensor is used to determine timing for starting purposes. The secondary engine speed/timing sensor is used to determine when the piston in the No. 1 Cylinder is at the top of the compression stroke. When the timing has been established, the primary engine speed/timing sensor is then used to determine engine speed.

Probable Causes:

1) ECM Connection/Harness
2) Timing sensor or brackets
3) Timing sensor harness
4) ECM Failure