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P2303 OBD-II Trouble Code: Ignition Coil “B” Primary Control Circuit Low

Check Engine Light

P2303 code definition

Ignition Coil “B” Primary Control Circuit Low

What the P2303 code means

P2303 is an OBD-II generic code for the engine control module (ECM) detecting a coil “B” primary control circuit low. This can be due to a short or open in the coil or in the wiring circuit to the coil's primary circuit.

What causes the P2303 code?

  • The engine control module (ECM) monitors the coil's primary control circuit and if the control circuit senses the voltage below specifications, then it will turn on the Check Engine Light and set code P2303.

  • The primary coil has internal shorted windings and causes the return voltage to go low.

  • The primary return wiring is shorted to ground or cut in the harness back to the ECM.

What are the symptoms of the P2303 code?

  • The Check Engine Light will be illuminated and the code is set in the ECM memory as a fault.

  • The engine will run very rough or not start at all depending on if the coil failure is intermittent or not.

  • The engine may run good and then all of a sudden stall or run very rough when short occurs.

How does a mechanic diagnose the P2303 code?

  • Scans for codes and documents any codes in the ECM, then looks at the freeze frame data for failure

  • Checks the coil for carbon tracking, cracks, or wiring harness cut into causing the short

  • Removes the coil connection and tests the coil for shorted primary windings

  • Checks the wiring harness for shorts or open circuits from coil to the ECM

Common mistakes when diagnosing the P2303 code?

  • Clearing ECM memory codes before checking the freeze frame data for the main failure problem, so the failure may be duplicated and repaired.

  • Replacing the coil when the harness has a short in the wiring and not doing a full diagnostic pinpoint check before replacing parts.

How serious is the P2303 code?

Code P2303 is a code indicating the coil's primary circuit has failed and most likely will result in a no start or stall of the engine since this is a second coil in a two coil engine.

What repairs can fix the P2303 code?

  • Repairing or replacing the coil wiring harness or connector
  • Replacing a shorted coil and checking the ECM for coil driver problems
  • Replacing the ECM due to a burned out coil driver circuit and replacing the coil

Additional comments for consideration regarding the P2303 code

Code P2303 is most commonly caused from an internal coil primary circuit short or open windings. The failure may burn out the ECM coil driver. If the coil and ECM are not replaced at the same time, the ECM may get burned out if it is replaced without a new coil also. Always check the coil's primary resistance for problems if replacing the ECM.

Need help with a P2303 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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