P2303 Low Ignition Coil B Primary Control Circuit

Fault Severity
The P2303 code indicates a serious problem requiring prompt diagnosis. Associated symptoms typically require immediate intervention to prevent engine damage.

Common Symptoms

• Engine misfires

• Reduced performance

• Increased fuel consumption

• Other related fault codes

• Possible deactivation of the affected cylinder’s injector by the PCM

Main Causes

• Blown fuse or faulty relay

• PCM (Powertrain Control Module) failure

• Damaged wiring (cuts, short circuits, rodent damage)

• Faulty ignition coil

• Failed camshaft/crankshaft sensor or defective wiring

Diagnostic Procedure

Required Equipment:

• OBD2 scanner

• Digital multimeter (DVOM)

• Vehicle technical documentation

Key Steps:

1. Check for TSBs: Consult Technical Service Bulletins (TSB) corresponding to your vehicle (model, engine) and symptoms for known solutions.

2. Read Codes:

   • Connect the scanner and retrieve all fault codes and freeze frame data.

   • Record them before clearing.

   • Test drive the vehicle: if the code reappears, continue; if the PCM enters “preparation mode,” the fault is intermittent.

3. Inspect Wiring:

   • Visually check wiring harnesses and connectors (especially for rodent damage).

   • Repair cut, burned, or damaged wires.

4. Test Ignition Coil:

   • Check voltage and ground at the affected coil using the DVOM.

   • No voltage? Check relays and fuses; replace if faulty.

5. Check PCM Signal:

   • Test the ground circuit at the PCM connector (with engine running).

   • Signal detected? Look for a break between PCM and coil.

   • No signal? Suspect PCM failure or programming error.

Important Note:
Rodent damage to wiring is a common cause of P2303, particularly in cold climates.