Diagnostic code: P0351
Decode: Malfunction in the ignition coil primary or secondary circuit
There is an open or short in the number 1 coil. Code detection: The modern engine uses a coil on plug system for the ignition. That means there is one coil for each of the cylinders, and they are controlled by the powertrain control module (PCM). When the coil is on the top of the spark plug, there is no need for any plug wires. There are two wires per coil. One is connected to the battery feed and the other is connected to the PCM. The PCM activates the coil and monitors the coil driver circuit for faults. Should there be a short or an open in coil number one, this code will display. The PCM may also shut down the cylinder’s fuel injection.
Symptoms of this code:
- The Malfunction Indicator Light (MIL) will usually illuminate right away
- There may be a misfire or intermittent misfire from the engine
What causes this code?
- There can be a short or ground of the coil on plug driver circuit
- There may be an open coil on plug driver circuit
- There can be a loose connection at the coil or the connector locks may be broken
- The coil on plug may be bad
- The PCM may be faulty
What the techs say:
If the misfire is intermittent, then test the wiring at the number 1 coil by wiggling it. Also, check the wiring harness that connects to the PCM. Repair any loose wires. Additionally, check the connection to the coil connector and make sure that the harness is routed correctly and is not visibly worn. Repair if necessary.
If the misfire is present, turn the engine off and disconnect the number 1 coil. Restart the engine and check for a signal to the coil. You can use a voltmeter in AC Hertz and look for an Hz reading that is between 5 and 20 on the scale. This will indicate that the driver is working. If you get a signal, then replace the number 1 coil since it is most likely a bad coil. If you do not get a signal, then disconnect the coil and check for DC voltage at the ignition coil connector’s driver circuit. If there is significant voltage, the short is in the voltage. Locate the short and make the repairs.
If you have no voltage to the driver circuit, then shut the ignition off, and disconnect the PCM. Look for continuity between the coil and the PCM. Repair the open or short if the continuity is disrupted. Should the continuity be intact, test the resistance between the ignition coil connector and the ground. It should have infinite resistance, and if not, repair the short.
The problem probably lies within the PCM coil driver if there is no open or short on the ignition coil driver, or if there is no trigger signal sent to the coil. If that driver is to blame, then there may be faulty wiring somewhere in the system that created the failure. When you replace the PCM, check the wiring to prevent another problem.
If the engine is not misfiring, but the code continues, you may need to replace the PCM coil monitoring system.