Powertrain Controls - ECM/PCM

Code Chart 42:

Ignition Circuit:

CIRCUIT DESCRIPTION:

When the distributor shaft rotates, a fluctuating magnetic field is generated due to changes in the air gap between the crank angle sensor and distributor shaft signal rotor. As a result, a small alternating current (AC) voltage is induced in the crank angle sensor. This ignition reference signal is sent to the ECM on terminals "B1" and "B9," 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. Code 42 will set if the following condition is met for 3 seconds: No ignition reference signal at the ECM.

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

1. Crank angle sensor contains a coil of very small wire. Its DC resistance is checked here.

2. When the distributor shaft turns, the crank angle sensor acts as an AC voltage signal generator. This checks for a proper AC signal voltage being produced.

3. After proving that the sensor is capable of generating the proper AC signal voltage, this step checks to see if this voltage is getting through to the ECM connector.

DIAGNOSTIC AIDS:

A loose or damaged crank angle sensor could cause an intermittent code. A misaligned crank angle sensor or improper air gap could result in Code 42 or intermittent cranks but won't run.