What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles. Although generic, specific repair steps may vary by make/model.
The COP (coil-on-plug) ignition system is what’s used on most modern engines. There’s an individual coil for each cylinder that’s controlled by the PCM (powertrain control module).
It eliminates the need for spark plug wires by placing the coil right above the spark plug. Two wires are dedicated to each coil. One is a battery feed typically from the electrical distribution center. The other wire is the coil control circuit from the PCM. The PCM grounds/ungrounds this circuit to activate or deactivate the coil. The coil control circuit is monitored by the PCM for faults.
If an open or short circuit is detected in the control circuit for coil number 1, a P0351 may be set. Additionally, depending on the vehicle, the PCM may also shut down the fuel injector for that cylinder as well.
Symptoms
Symptoms of a P0351 DTC may include:
• MIL (malfunction indicator lamp) illumination
• Engine misfire may be present or intermittent
Causes
Potential causes of a P0351 code include:
• Short to voltage or ground on COP driver circuit
• Open in COP driver circuit
• Loose connection at coil or broken connector locks
• Bad coil (COP)
• Faulty powertrain control module
Possible Solutions
Is the engine currently misfiring? If not, the problem is likely intermittent. Try testing the wiring at coil #1 and along the wiring harness to the PCM. If manipulating the wiring causes a surface misfire, repair the wiring issue. Check for poor connection at the coil connector. Verify the harness isn’t misrouted or rubbing against anything. Repair as necessary.
If the engine is currently running rough, stop the engine and disconnect the wiring connector from coil #1. Then start the engine and look for a driver signal to coil #1. Using a scope will give you a visual pattern to observe, but since most people don’t have access to one, there’s a simpler way. Use a voltmeter on the AC Hertz scale and see if there’s a Hz reading between 5 and 20, indicating the driver is working. If there’s a Hertz signal, replace ignition coil #1. It’s likely bad. If you detect no frequency signal from the PCM on the ignition coil control circuit, indicating the PCM is grounding/ungrounding the circuit (or if there’s no visible pattern on the oscilloscope if you have one), leave the coil disconnected and check DC voltage on the trigger circuit at the ignition coil connector. If there’s significant voltage on that wire, there’s a short somewhere. Find the short and repair it.
If there’s no voltage on the trigger circuit, turn off the ignition. Disconnect the PCM connector and check continuity of the driver between the PCM and the coil. If there’s no continuity, repair the open circuit or short to ground in the circuit. If continuity is present, check resistance between ground and the ignition coil connector. There should be infinite resistance. If there isn’t, repair the short to ground in the coil control circuit.
NOTE: If the ignition coil driver signal wire isn’t open or shorted to voltage or ground and there’s no trigger signal to the coil, suspect a faulty PCM coil driver. Also keep in mind that if the PCM driver has failed, there may be a wiring problem that caused the PCM to fail. It’s a good idea to perform the above check after PCM replacement to verify there won’t be a repeat failure. If you find the engine isn’t misfiring, the coil is being triggered properly but P0351 keeps resetting, it’s possible the PCM coil monitoring system is faulty.