Open or damaged wire in the coil 'B' primary control circuit, such as a broken conductor or corroded connector; Failed ignition coil 'B' with an open primary winding; Faulty PCM driver for that coil circuit, though this is less common; Poor electrical connection at the coil or PCM connector, including backed-out pins; Short to voltage on the control wire from chafed insulation; Aftermarket alarm or remote start wiring that has tapped into the coil circuit

DTC codes / P23xx · Ignition system and misfire / P2304

P2304Ignition Coil 'B' Primary Control Circuit High

Q: What does code P2304 mean?

Ignition Coil 'B' Primary Control Circuit High. P2304 means the engine computer (PCM) has detected an abnormally high voltage on the primary control circuit for ignition coil 'B', which usually points to an open circuit or a coil driver that cannot pull the control wire low. The PCM commands the coil to fire by grounding the primary circuit, and when it sees the voltage stay high instead of dropping, it flags this code.

P2304 means the engine computer (PCM) has detected an abnormally high voltage on the primary control circuit for ignition coil 'B', which usually points to an open circuit or a coil driver that cannot pull the control wire low. The PCM commands the coil to fire by grounding the primary circuit, and when it sees the voltage stay high instead of dropping, it flags this code.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Check engine light illuminated, often with no other noticeable symptoms
Engine misfire or rough running, especially under load or acceleration
Reduced engine power or a limp-home mode in some vehicles
Shaking or vibration felt through the steering wheel or seat
Difficulty starting or a stalled engine in more severe cases
A slight fuel smell or poor fuel economy from unburned fuel

Common causes, most likely first

Open or damaged wire in the coil 'B' primary control circuit, such as a broken conductor or corroded connector
Failed ignition coil 'B' with an open primary winding
Faulty PCM driver for that coil circuit, though this is less common
Poor electrical connection at the coil or PCM connector, including backed-out pins
Short to voltage on the control wire from chafed insulation
Aftermarket alarm or remote start wiring that has tapped into the coil circuit

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm the fault is current and not history
Inspect the coil 'B' connector and the PCM connector for corrosion, loose pins, or damage
Measure resistance of the coil 'B' primary winding and compare with the manufacturer's specification
Check the control wire from the coil to the PCM for continuity and for shorts to voltage or ground
Swap coil 'B' with a known-good coil of the same part number and see if the code follows the coil
If the circuit and coil test good, use a lab scope to verify the PCM driver signal at the coil connector
Repair or replace the faulty wire, connector, coil, or PCM as indicated by the tests

What a high primary circuit really means

A high voltage on the primary control circuit almost always means the circuit is open, so the PCM cannot ground the coil to fire it, rather than a shorted coil.
Technicians often replace the coil first, but a chafed wire or a corroded connector pin is just as likely and much cheaper to fix.
The code can be set by a faulty PCM driver, but that should only be suspected after the wiring and coil have been ruled out with a scope.
Some vehicles use a single coil per cylinder, while others use a coil pack; the diagnostic steps are the same, but the coil location and connector style vary.
A coil 'B' circuit fault can cause a misfire that is not always felt by the driver, so do not assume the engine is running fine just because the light is on.

Can I keep driving with P2304?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or towing because a persistent misfire can overheat the catalytic converter. If the engine is running very rough or flashing the check engine light, stop driving and have it 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.