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P2303: Ignition coil B primary control circuit low

The ECU sees too low a voltage on the control wire of ignition coil B. Usually a wire shorted to earth, the connector or the coil.

Code P2303 at a glance
CodeP2303
SystemEngine and transmission
GroupP23xx, Ignition coils and engine
TypeGeneric: it means the same on every make
Can you keep driving?Better not

What P2303 means

The ignition coil turns battery current into the high voltage that makes the spark at the plug. The ECU switches it through the primary circuit. Circuit low means the ECU sees a voltage below what it expects on that wire, usually because it is touching earth or the coil has failed. Which coil is coil B is decided by each manufacturer; on many engines with one coil per cylinder it matches a specific cylinder.

Most common causes

  • Loose, broken or corroded coil connector
  • Failed ignition coil
  • Control wire chafed and touching earth
  • Fault in the coil power supply (fuse or relay)
  • Fault in the ECU drive circuit (uncommon)

Symptoms

  • Engine warning light on or flashing
  • Jerking and misfires
  • Rough idle, engine shaking
  • Loss of power and higher fuel consumption

Can you drive with P2303?

Better not Best not to drive, or only as far as you must: a cylinder with no spark sends unburnt fuel into the exhaust and can damage the catalyst. If the light flashes, stop as soon as it is safe.

How to check it

Check for misfire codes on a specific cylinder at the same time (P0301, P0302 and so on); they tell you which coil to look at. With the engine off, make sure its connector is fully home; with individual coils, swapping it with another cylinder and seeing if the misfire moves confirms the fault.

How to read and clear P2303 with Final OBD

Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P2303 with this same explanation and whether it’s confirmed, pending or permanent.

With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.

Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

P2303 is a generic code, so it means the same on any make, for example on Abarth, Alfa Romeo, Cupra, Jeep, Nissan, Škoda. See what Final OBD does on your car in makes and models.

What does code P2303 mean?

The ignition coil turns battery current into the high voltage that makes the spark at the plug. The ECU switches it through the primary circuit. Circuit low means the ECU sees a voltage below what it expects on that wire, usually because it is touching earth or the coil has failed. Which coil is coil B is decided by each manufacturer; on many engines with one coil per cylinder it matches a specific cylinder.

Can you drive with P2303?

Best not to drive, or only as far as you must: a cylinder with no spark sends unburnt fuel into the exhaust and can damage the catalyst. If the light flashes, stop as soon as it is safe.

How do you clear P2303?

With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P2303 comes back.