DTC 42

Diagnostic Chart:

Camshaft Position Sensor Circuit:

CIRCUIT DESCRIPTION
When the distributor shaft rotates, a fluctuating magnetic field is generated due to changes in the air gap between the Camshaft Position (CMP) sensor and distributor shaft signal rotor. As a result, a small Alternating Current (AC) voltage is induced in the CMP sensor. This ignition reference signal is sent to the Engine Control Module (ECM) on terminals "B7" and "B15" where the ECM monitors the AC voltage between these two terminals. The ECM uses this signal in determining when to fire the ignition coil and the fuel injector.

Diagnostic Trouble Code (DTC) 42 will set if the following condition is met for 2 seconds: No ignition reference signal at the ECM while the engine is cranking.

DTC CHART TEST DESCRIPTION
Numbers below refer to the circled numbers on the diagnostic chart.

1. The CMP sensor's resistance check is 205-255 ohms at 20°C (68°F).
2. When the distributor shaft turns, the CMP sensor acts as an AC voltage signal generator. This checks for a proper AC signal voltage being produced.
3. After proving that the CMP sensor is capable of generating the proper AC signal voltage, this step checks to see if this voltage is getting through to the ECM.

DIAGNOSTIC AIDS
A loose or damaged CMP sensor could cause an intermittent DTC.

A misaligned CMP sensor or improper air gap could result in DTC 42 or intermittent "cranks but won't run." Refer to Computer and Control Systems / Camshaft Position Sensor for specifications and additional information. Camshaft Position Sensor

Resistance of the CMP sensor will increase as engine temperatures increase.

DTC 42 will set in history only.

INTERMITTENT MALFUNCTIONS
An intermittent malfunction may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.