The CMP signal is required by the IDM/PCM to activate the individual fuel injectors according to the injection sequence. The CMP sensor works on the Hall principle.
The square-wave signal is used to identify cylinder 1, in conjunction with the CKP signal.
Effects of faults
During the engine start the CKP signal and the CMP signal are synchronized. If the CMP signal is not detected by the engine management system, no start release is issued. This means the injected fuel quantity is set to 0.
In the vehicles used, two different synchronization trategies are implemented in the engine management software.
Strategy 1:
โข If the CKP signal fails while the engine is running, the engine cuts out immediately and it is not possible to re-start it.
Strategy 2:
โข If the signal fails while the engine is running, the engine continues to run without restrictions.
However, it is not possible to re-start the engine after it has been switched off.
Diagnosis
Parallel to the CKP signal the CMP signal occurs. After it has been ensured that the CKP signal is OK, the system is able to ascertain a fault in the CMP circuit.