Revolutions Per Minute (RPM) represents the rotational speed of the engine crankshaft. The Engine Control Unit (ECU) derives this value by monitoring the frequency of pulses generated by the Crankshaft Position (CKP) sensor.

Signal Characteristics#

The ECU calculates engine speed based on the pulse train received from the CKP sensor.

• Pulse Frequency: The standard Honda CKP sensor configuration generates 2 pulses per 1 full crankshaft revolution.
• Calculation: The ECU measures the time interval between these pulses to determine the instantaneous RPM.

Note

Variations in pulse patterns may exist depending on the specific engine management system and the number of teeth on the crankshaft trigger wheel. Always verify against the specific ECU pinout and service manual for your chassis.

Diagnostic Considerations#

If the ECU fails to receive a consistent signal from the CKP sensor, the following symptoms typically occur:

• No Start / Stall: The ECU cannot synchronize fuel injection or ignition timing without a valid RPM signal.
• Erratic Tachometer: The dashboard tachometer signal is often driven by the ECU based on the processed CKP input; an unstable signal will result in a fluctuating or dead tachometer needle.
• Diagnostic Trouble Codes (DTCs): Failure of the CKP circuit will trigger specific ignition or sensor-related error codes.