With the ignition off, disconnect the engine management system wiring harness connector from the phase sensor (see Removal the phase sensor).
To check the sensor power supply circuit…
…we connect the tester probes to terminals "B" and "C" of the wiring harness block.
When the ignition is on, the voltage should be equal to the voltage of the on-board network.
Otherwise, check the integrity of fuse F14 (15A) of the mounting block located in the passenger compartment, and the serviceability of the circuit (open circuit and short circuit to ground) between terminal "C" of the wiring harness block and the mounting block.
We also check the serviceability of the circuit between terminal "B" of the wiring harness connector and the "ground".
If the circuits are in good condition and there is no voltage, the ECU is faulty.
We connect the tester probes to terminals "A" and "C" of the wiring harness block.
With the ignition on (and in the absence of a phase sensor signal) the tester should record a voltage between terminals "A" and "C" of about 6.5–7.0 V (at a voltage of 12.0 V at the battery terminals).
Otherwise, we check the serviceability of the circuit (open circuit and short circuit to ground) between the "M26" terminal of the ECU harness connector and the "A" terminal of the wiring harness connector.
If the circuits are in good condition and there is no voltage, the ECU is faulty.
To check the phase sensor, we dismantle it (see Removal the phase sensor) and connect the wiring harness block to the sensor.
From the side where the wires enter the block, we insert two pieces of wire into its sockets corresponding to terminals "A" and "C" so that contact appears between them and the terminals of the wires.
We set the tester to the AC voltage measurement mode (0–20 V).
We connect the tester probes to the pieces of wire.
Turning on the ignition…
…we pass a steel plate in front of the sensor rod several times.
In this case, the device of a serviceable sensor should record abruptly changing voltage values.
We replace the faulty sensor with a new one.
(The article was reprinted from the website: «chevyman»)