P0321 indicates the powertrain control module (PCM) has detected an implausible, erratic, or out-of-range signal from the engine speed sensor located within the distributor. This circuit tells the computer the crankshaft’s position and speed so it can time ignition and fuel injection; a fault here typically causes a no-start or stall condition.
The magnetic pickup or Hall-effect sensor inside the distributor that generates the engine speed signal has failed internally, often from heat cycling or age, producing no signal or an erratic waveform.
Open circuits, short-to-ground, or high resistance in the harness between the distributor and PCM—commonly caused by chafing, corrosion at pins, or moisture intrusion—disrupt the reference voltage or signal return.
The toothed trigger wheel (reluctor) inside the distributor may be cracked, corroded, or coated in metallic debris, altering the magnetic field and producing an inconsistent signal.
Excessive shaft bearing wear or wobble changes the air gap between the pickup coil and reluctor wheel, leading to weak or intermittent pulses that the PCM interprets as a range/performance error.
If the distributor was recently removed or replaced, improper seating or an incorrect air gap can cause the signal to fall outside expected parameters.
Rarely, the PCM’s input circuitry fails to correctly interpret a good sensor signal; this should only be considered after the sensor, wiring, and mechanical integrity have been verified good.
No. The engine may stall without warning or fail to restart, creating a hazardous situation in traffic. Repair the fault before driving.
Functionally yes—it provides the crankshaft’s speed and position to the PCM. On distributor-equipped engines, this sensor is housed inside the distributor rather than on the crankshaft itself.
Almost never. PCM failure is extremely rare for P0321; the problem is almost always a bad pickup coil, wiring corrosion, or connector issues. Verify the sensor and circuit integrity before considering a PCM.
Heat expands components and can open marginal solder joints in the pickup coil or increase resistance in weak wiring, causing the signal to drop out once the engine warms up.