What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles (Hyundai, Toyota, Chevy, Ford, Dodge, Chrysler, etc.). Although generic, the specific repair steps may vary depending on the make/model.
If your OBD-II vehicle has stored a P0350 code, it means the Powertrain Control Module (PCM) has detected a problem with the primary and/or secondary circuit for one or more ignition coils or ignition coil packs.
Most OBD-II equipped vehicles use a distributorless, coil-on-plug ignition system. In this type of system, each cylinder is equipped with its own ignition coil that is attached to the spark plug using a short spark plug wire or a silicone boot. Battery voltage and a ground pulse from the PCM applied to a tightly wound induction coil create the high-intensity spark (thousands of volts) needed to fire the spark plug for each cylinder.
Systems that use coil packs operate similarly, except that multiple spark plugs are fired from a single coil pack that fires several cylinders in a sequential order. This type of system typically uses longer high-tension spark plug wires to transfer the high-intensity spark from the coil pack towers to the spark plugs.
Regardless of the type of ignition system the vehicle in question is equipped with, the timing and function of the sparks are controlled by the PCM. Provided with a constant supply of switched battery voltage (with the ignition switch in the ON position), the ignition coil releases a high-intensity spark when it receives a ground pulse from the PCM.
If the PCM detects that any of the ignition coil circuits are not completed when the ground pulse is applied, a P0350 code will be stored and a Malfunction Indicator Lamp (MIL) may be illuminated.
Code Severity and Symptoms
Misfire issues will likely accompany a P0350 code; therefore, it should be classified as severe.
Symptoms of this code may include:
Driveability issues, including one or more misfires
Poor engine performance
Reduced fuel economy
Cylinder misfire codes will likely accompany a P0350 code (e.g., P0301, P0302, P0303, P0304, etc.)
Causes
Possible causes for this code being set are:
Open or shorted primary/secondary circuits
Faulty ignition coils or coil packs
Bad ignition system relay
Blown fuses or fusible links
Faulty PCM or PCM programming error
Diagnostic and Repair Procedures
To diagnose a P0350 code, I would need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information, such as ALLDATA (DIY).
A visual inspection of all ignition coil/pack wiring and connectors is the best place to start your diagnosis of a P0350 code. Look for broken electrical connectors at the ignition coils or coil packs. Also check for burned, broken, or corroded wiring. I have personally found rodent-damaged wiring to be the cause of a P0350 code in several customer cars. The terminals of the ignition coil electrical connectors are also known to corrode over time.
I would continue by connecting the scanner to the vehicle’s diagnostic port and retrieving all stored codes and freeze frame data. I have found it useful to record this information for later. Then, I would clear the codes and take a test drive to see if the P0350 resets.
Use your vehicle information source to research any Technical Service Bulletins (TSBs) that may assist in your diagnosis. TSBs with matching symptoms and codes can prove very helpful if you use the diagnostic tips contained within them.
If there are cylinder-specific ignition coil primary/secondary circuit codes, they can help you pinpoint the faulty circuit or coil/pack. If there are no cylinder-specific codes, you will need to determine which coil, coil pack, or circuit is malfunctioning. This can be done by testing the coils or coil packs for the correct level of Hertz when a high-intensity spark is emitted, but I use a simpler method. With the engine running and the parking brake firmly set, I use an assistant to sit in the driver’s seat. They firmly press the brake pedal, put the transmission in gear, and press the accelerator pedal lightly but progressively. When the engine begins to misfire, my assistant holds the accelerator pedal in that position, while I systematically remove each spark plug wire/boot from the spark plug (you can also unplug each coil pack’s electrical connector if you prefer, to avoid the risk of being exposed to over 50,000 volts of high-intensity spark).
When you find a coil or coil tower that makes no difference in engine RPM when the spark plug wire/boot is removed from the spark plug; you have found the cylinder number of the faulty coil/pack. You will likely notice that the level of high-intensity spark emitted by the faulty coil/pack is significantly lower than those operating correctly. Be sure to clear the codes after performing this test. Once you have located the coil/pack in question, use the DVOM to test for battery voltage at the coil/pack connector with the ignition on. If there is no voltage, use the vehicle information source to find the voltage source to check for blown fuses, faulty relays, etc. If all fuses and relays are good, use the DVOM to probe individual circuits for continuity and resistance. Disconnect all associated controllers before doing this to avoid damaging sensitive onboard electronics. Repair or replace any circuits that do not meet the manufacturer’s specifications (found in the vehicle information source).
If the voltage signal is present at the ignition coil/pack, test the coil connector for a ground pulse from the PCM. If no ground pulse is present (while the engine is running or cranking), suspect a faulty driver inside the PCM if no other ignition-related codes (including crankshaft position sensor and camshaft position sensor codes) are present.
Additional Diagnostic Notes:
A maintenance tune-up is NOT a solution for a P0350 code
Use caution when testing a high-intensity spark near flammable fluids