Technical Description of OBD-II Trouble Code
Malfunction in the Primary/Secondary Circuit of Ignition Coil A
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
Most modern engines use the COP (coil on plug) ignition system. Each cylinder has an individual coil controlled by the PCM (powertrain control module).
This system eliminates the need for spark plug wires by placing the coil directly above the spark plug. Each coil is connected by two wires. One wire is a battery feed typically from the power distribution center, while the other wire is the coil driver circuit from the PCM. The PCM grounds or ungrounds this circuit to activate or deactivate the coil. The PCM monitors the coil driver circuit for any faults.
If an open or short is detected in the driver circuit for coil number 1, a P0351 code may be set. Additionally, depending on the vehicle, the PCM may also shut down the fuel injector to the cylinder.
Symptoms
The symptoms of a P0351 DTC may include:
Causes
The potential causes of a P0351 code include:
Possible Solutions
Is the engine currently misfiring? If not, the problem is likely intermittent. Try wiggling the wiring at the #1 coil and along the wiring harness to the PCM. If manipulating the wiring causes the misfire to occur, repair the wiring issue. Check for a poor connection at the coil connector. Verify that the harness is not misrouted or chafing against anything. Repair as necessary.
If the engine is currently misfiring, stop the engine and disconnect the wiring connector for the #1 coil. Then, start the engine and check for a driver signal to the #1 coil. Using a scope will provide a visual pattern to observe, but if a scope is not available, there is an easier method. Use a voltmeter in AC Hertz scale and check for a reading between 5 and 20 Hz, indicating that the driver is functioning. If there is a Hertz signal, replace the #1 ignition coil as it is likely faulty. If no frequency signal is detected from the PCM on the ignition coil driver circuit (or there is no visible pattern on the scope), leave the coil disconnected and check for DC voltage on the driver circuit at the ignition coil connector. If there is significant voltage on that wire, there is a short to voltage somewhere. Locate and repair the short.
If there is no voltage on the driver circuit, turn off the ignition. Disconnect the PCM connector and check the continuity of the driver between the PCM and the coil. If there is no continuity, repair the open or short to ground in the circuit. If continuity is present, check for resistance between ground and the ignition coil connector. There should be infinite resistance. If not, repair the short to ground in the coil driver circuit.
NOTE: If the ignition coil driver signal wire is not open or shorted to voltage or ground and there is no trigger signal to the coil, suspect a faulty PCM coil driver. Also, keep in mind that if the PCM driver is at fault, there may be a wiring problem that caused the PCM failure. It is advisable to perform the above check after PCM replacement to ensure there will not be a repeat failure. If the engine is not misfiring, the coil is being triggered properly, but the P0351 code continues to be reset, there is a possibility that the PCM coil monitoring system may be faulty.
