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DTC codes / P23xx · Ignition system and misfire / P2305

P2305Ignition Coil 'B' Secondary Circuit

P2305 indicates that the powertrain control module (PCM) has detected an abnormal condition in the secondary circuit of ignition coil 'B', which is the high-voltage side that fires the spark plug. The PCM monitors the coil's secondary circuit for expected electrical behavior and sets this code when the signal does not match the stored profile.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Engine misfire or rough running, especially under load or acceleration
  • Reduced engine power or a limp-home mode
  • Shaking or vibration felt through the steering wheel or seat
  • Poor fuel economy or a strong fuel odor from the exhaust
  • Difficulty starting or an engine that stalls shortly after startup

Common causes, most likely first

  1. Faulty ignition coil 'B' with an open or shorted secondary winding
  2. Worn or fouled spark plug causing excessive secondary circuit resistance
  3. Damaged or corroded secondary ignition wire or boot
  4. Poor electrical connection at the coil primary connector or ground
  5. PCM internal fault or corrupted software affecting coil monitoring
  6. Engine mechanical issue such as low compression or a vacuum leak that mimics a coil fault

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, and record freeze-frame data to understand when the fault occurs
  2. Perform a visual inspection of ignition coil 'B', its connector, and the secondary wire for cracks, corrosion, or damage
  3. Swap ignition coil 'B' with a known-good coil from another cylinder and see if the misfire or code follows the coil
  4. Check the spark plug condition and gap, and replace if worn, fouled, or incorrect
  5. Measure the secondary circuit resistance with a multimeter and compare to the manufacturer's specification
  6. Test the coil's primary circuit for power and ground with a test light or multimeter while cranking
  7. If all electrical checks pass, consult factory service information for PCM testing or reprogramming procedures

What the secondary circuit code really means

  • A P2305 can be set by a spark plug that is worn or incorrectly gapped, even when the coil itself is perfectly healthy.
  • The code often appears after a coil has been replaced without clearing adaptive learning, causing the PCM to misinterpret the new coil's signal.
  • Secondary circuit faults can be intermittent and only set the code under specific load or temperature conditions, so a simple key-on test may not reveal the problem.
  • A misfire from a mechanical issue like a bad valve or piston ring can create secondary circuit anomalies that mimic a coil failure, leading to unnecessary coil replacement.
  • Some vehicles use a waste-spark system where one coil fires two cylinders, so a fault in the secondary circuit can affect two cylinders and set misfire codes for both.

Can I keep driving with P2305?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration, towing, or long trips because a persistent misfire can overheat the catalytic converter and cause costly damage. If the check engine light is flashing, stop driving and have the vehicle towed.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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