This Article Contains
- What Is Code P0351?
- What Does The P0351 Code Mean?
- What Triggers Code P0351?
- Symptoms Associated With The P0351 Code
- Is The P0351 Code Critical?
- How Is The P0351 Code Diagnosed?
- How Is The P0351 Code Fixed?
- A Reliable Solution To The P0351 Code
- 4 P0351 FAQs
Let’s get started.
What Is Code P0351?
Code P0351 is defined as “Ignition Coil ‘A’ Primary/Secondary Circuit Malfunction.”
It’s an OBD-II diagnostic trouble code (DTC) that indicates a fault with ignition coil ‘A’ (a problem with the coil on cylinder #1 or its circuit).
The P0351 code is a generic DTC — meaning it indicates the same issue for any vehicle that supports an OBD-II system. Even so, steps to resolve the malfunction may depend on the make and model of the car.
Your mechanic may need to refer to the appropriate factory service manual and wiring diagram to conduct repairs.
What Does The P0351 Code Mean?
The powertrain control module (PCM) sets code P0351 when it detects a malfunction in cylinder #1’s ignition coil or its circuit.
Why is it only for cylinder #1?
The ignition system on most modern engines uses individual ignition coils for each cylinder. The PCM monitors and controls the operation of each ignition coil.
When the PCM doesn’t detect specific signals that it expects from the coil pack circuit, it will set the error code P0351-P0362, depending on which cylinder’s ignition coil has the problem.
The last digit of the code refers to the cylinder with the issues.
As a result, P0351 is the code for cylinder #1 (ignition coil A), and P0352 is for cylinder #2 (ignition coil B), and so on. These codes go all the way to code P0360, which indicates a coil circuit fault in cylinder #10 (ignition coil J) for a V10 or V12 engine.
Now that we’ve got the definition out of the way, let’s see what faults prompt this trouble code to appear.
What Triggers Code P0351?
There can be many triggers for the P0351 error code.
- A defective ignition coil
- Problems with the ignition circuit
- Spark plug or spark plug wire malfunction
- An open or short in the ignition coil wiring harness
- Defective coil wiring connector
- A vacuum leak in the intake manifold
- Carbon buildup in the air passages of the throttle body
- A problem with the PCM (this is very rare)
With these causes, what symptoms are likely to turn up?
Symptoms Associated With The P0351 Code
Your car may exhibit more than one symptom with the P0351 code.
These are the ones frequently encountered:
- The dashboard Check Engine light (Malfunction Indicator Lamp) turns on
- A rough or erratic engine idle
- Engine misfire, either intermittently or continuously
- The engine lacks power, especially under heavy load
- The car has trouble starting
Note: An ignition coil malfunction also often triggers the misfire codes P0301-P0312 which indicate which cylinder has a misfiring issue.
With all this in mind, you’ll probably want to know how serious code P0351 is.
Is The P0351 Code Critical?
It depends on how severe the symptoms are, as some may present drivability issues.
If the car doesn’t start, you won’t be able to drive it in the first place.
If the engine is misfiring, you probably can still drive, but leaving the misfire as it is can damage the engine over time.
And while rare, a P0351 code from a faulty PCM could bring on a whole barrage of issues that could manifest in tons of safety concerns.
The general consensus is that while code P0351 shouldn’t prevent you from driving your car, resolving it should be made a priority.
How Is the P0351 Code Diagnosed?
To begin diagnosis, your mechanic will use a scan tool to check the codes stored in the PCM, including any freeze frame data.
They’ll clear the codes and then test-drive the car in similar conditions to duplicate the error. The data stream on the scan tool can tell them if the problem is on a specific cylinder or all of them.
Troubleshooting this code isn’t entirely straightforward, so your mechanic will:
- Visually inspect the coil pack, coil connector and wiring for any worn or damaged parts
- Inspect the spark plug and spark plug wiring
- Check the voltage on the coil driver circuit
- Test the electrical continuity and resistance at the coil driver circuit
- Check for damage on a crankshaft sensor
- Test the powertrain control module and its circuit if issues are not detected elsewhere
This code should be investigated thoroughly. Replacing parts without testing, or skipping diagnosis steps, may cause the code to return. For example, a simple component like a loose or bent connector pin could still cause issues.
How Is The P0351 Code Fixed?
The types of repairs for the P0351 code vary based on what’s caused it.
Repairs could include:
- Replacing the ignition coil
- Replacing the spark plug and spark plug wire
- Repairing or replacing an ignition coil connector
- Repairing any other electrical wiring or connector faults
- Replacing the throttle body
- Repairing or replacing the PCM
However, is there a simple, reliable way to resolve code P0351?
A Reliable Solution To The P0351 Code
To ensure your P0351 code goes away for good, you’ll want a reliable mechanic to diagnose the code and conduct thorough repairs.
All the better if they’re mobile mechanics who can pop by your home (especially if your car has trouble starting). Then you won’t have to drive a problematic car to an auto shop.
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We’ve now gone through the basics of the P0351 code.
Next, let’s move on to some FAQs.
4 P0351 FAQs
Here are answers to some P0351 code-related questions.
1. How Does The Ignition System Work?
The ignition system converts the voltage delivered from the battery into a higher voltage. This high voltage is used to fire the spark plug, which ignites the cylinder air and fuel mixture.
In modern engines, a coil pack — comprising several ignition coils — is placed on top of the spark plug for each cylinder.
Every ignition coil has a “primary” winding and a “secondary” winding. The primary side has a couple hundred turns of wire, while the secondary side has thousands of wire turns.
The low voltage half of the system is called the primary ignition circuit. This includes the battery, ignition switch, primary coil winding, a triggering mechanism (like the crankshaft sensor), and a switching device that acts as an igniter (usually the PCM).
The high voltage half of the system is referred to as the secondary ignition circuit and includes the secondary coil winding and spark plug array.
What happens at the ignition coil?
When the ignition switch is turned, a current is applied to the primary circuit, creating a magnetic field around the primary winding.
The current in the primary circuit is interrupted by the ignitor, causing the magnetic field to collapse. This collapse induces a voltage into the secondary winding.
The secondary winding has more turns of wire, therefore increasing the output voltage to an amount sufficient for spark plug firing.
2. What Are The PCM and ECM?
PCM stands for Powertrain Control Module.
ECM is short for Engine Control Module.
The terms are often used interchangeably to represent the car’s onboard computer, though to be specific, they aren’t exactly the same.
The powertrain control module controls everything — from engine timing, fuel pump function to gear transmission. However, it isn’t very involved in manual transmission.
The engine control module, technically, only controls the engine, but not the transmission. A car could have a manual transmission and an ECM, or sometimes the transmission is controlled by a separate system called the Transmission Control Module (TCM).
3. What’s A Crankshaft Sensor?
The crankshaft sensor (or crank sensor) detects the exact position and measures the rotational speed (RPM) of the engine crankshaft.
The powertrain control module (PCM) reads this data to determine when to generate a spark and in which engine cylinder. The crankshaft’s position also tells the PCM if there’s a cylinder misfire.
If the crank sensor signal is missing, there won’t be any spark or fuel injector operation.
4. What’s A Crankshaft?
Each piston is attached to the crankshaft and a camshaft.
The camshaft controls the movement of piston valves for intake and exhaust airflow. The piston’s up and down movement (from internal combustion action) drives the crankshaft.
The crankshaft converts the vertical movement of the pistons into the rotational movement needed to put a car in motion.
Synchronization of the movement between camshaft and crankshaft is critical to how well an engine performs.
The P0351 code can have many different causes, and a faulty ignition coil shouldn’t be left unattended for long.
Remember, your engine is the core of your car, so it’s always a good idea to let a professional deal with any engine issues — be it a coil driver circuit short, faulty fuel injector, or fuel pump.
To keep any worries at bay, let RepairSmith handle it for you. Just contact them, and their ASE-certified mechanics will be at your disposal in no time!