Engine Speed Signals

Engine Speed TD: The "TD" signal is produced by the ECM as an output function. The TD signal is a processed signal that indicates engine speed (RPM) The signal is made available to other control units including the Instrument Cluster, EML, EGS etc.

The TD output is a square wave modulated signal. The frequency of the signal is directly proportional to RPM. The receiving control module detects RPM by the number of pulses.

Engine Speed TR: The "TR" signal is an additional variation of the engine speed signal. The TR signal is produced by the M70 & S38 M1.2 & M1.7 ECM systems as an additional output function. Like TD, TR is a processed signal that indicates engine speed (RPM).

The TR signal is a pulse wave signal (sine wave). The frequency of the signal directly proportional to RPM.


NOTE: On vehicles systems that use TR as an input, the signal is overlapped on the fuel pump relay control signal from the DME control module.