Ignition Hall Effect Sensor: Description and Operation

LOCATION

Housed in distributor.

PURPOSE

The Powertrain Control Module (PCM) uses this input to determine engine speed and crankshaft position, and adjusts ignition timing, fuel injection, and idle speed accordingly.

OPERATION

Pick-up generates pulses when slots pass between Light Emitting Diodes (LED's) and photo diodes.

Optical Distributor Top View:

Optical Distributor Cut Away View:

THEORY

A disk, with 2 sets of slots, spins at half engine speed, between two LED/photo diode pairs (optical sensors).

The outer or "high data rate", slots pass through the corresponding sensor at a rate of 1 slot per 2 degrees of crankshaft rotation.

The inner, or "low data rate", set of 6 slots, correspond to top-dead-center for each piston.

The "high data rate" signal is used to control ignition timing for engine speeds up to 1200 RPM, because during cranking and at idle, engine speed changes with the firing pulse of each cylinder.

Above 1200 rpm, speed changes due to individual firing pulses are negligible. Therefore the "Low data rate" slots are used to time fuel injection and ignition at engine speeds above 1200 RPM.

If the PCM does not detect input from the pick-up, the PCM de-activates the ASD and fuel pump relays, interrupting power to the fuel pump, injectors, coil, and oxygen sensor heater, preventing fuel injection and ignition, (a no start condition).