Code 42 (Standard Emissions) - Camshaft Position Sensor Circuit, No Signal For 2 Seconds: Notes

When distributor shaft rotates, a fluctuating magnetic field is generated due to changes in air gap between Camshaft Position (CMP) sensor and distributor shaft signal rotor. As a result, a small AC voltage is induced in CMP sensor. This ignition reference signal is sent to ECM on ECM terminals B1 and B9. ECM monitors AC voltage between these terminals. ECM uses this signal in determining when to fire ignition coil and fuel injector. Code 42 will set when ignition reference signal is not present at ECM for 2 seconds.

1. Checks Camshaft Position (CMP) sensor resistance.
2. Checks for a proper AC signal voltage being produced. When distributor shaft turns, CMP sensor acts as an AC voltage signal generator.
3. Checks if proper AC signal voltage is getting through to ECM.