P2303 means the powertrain control module has detected a lower-than-expected voltage on the primary control circuit for ignition coil B. This low-voltage condition typically results from a short to ground, an internal coil fault, or a wiring problem that prevents the circuit from reaching normal operating voltage. When this happens, the coil may not fire properly and the affected cylinder can misfire.
Internal shorting or degradation of the coil’s primary winding can pull the control circuit voltage low, causing the PCM to set this code. This is the most common root cause.
Chafed, melted, or damaged insulation in the harness between the PCM and coil can create an unintended path to ground that holds the circuit voltage below threshold.
Moisture intrusion, burned terminals, or poor pin fit at the coil connector can introduce excessive resistance or a partial short that affects primary circuit voltage.
A broken wire, backed-out pin, or severe corrosion can prevent the circuit from developing normal voltage when the PCM attempts to operate the coil driver.
An internal failure of the PCM’s coil driver transistor is uncommon but possible; it should only be considered after the coil, wiring, and connectors have been thoroughly tested and verified good.
Continued driving is not recommended. A misfire from coil B can overheat and destroy the catalytic converter, and the engine may run poorly or stall unexpectedly.
Not necessarily. While the coil itself is the most common failure, the wiring and connector should be inspected and tested first to avoid unnecessary replacement.
No. PCM failure is rare for P2303. Most cases are caused by a faulty coil or a circuit issue, and the PCM should not be replaced until all other possibilities are ruled out.
The specific cylinder or coil position varies by engine design and manufacturer. Consult the vehicle’s service information to identify the exact coil and cylinder assignment.