If your OBD-II scanner displays P0351, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected a malfunction in the Ignition Coil “A” Primary/Secondary Circuit.
The generic OBD-II definition for P0351 is:
Ignition Coil “A” Primary/Secondary Circuit Malfunction
On most vehicles, Ignition Coil “A” refers to the ignition coil serving Cylinder 1, although the exact cylinder assignment varies by manufacturer. The PCM continuously monitors the ignition coil’s electrical circuit to ensure it receives the correct voltage, ground, and switching signals needed to generate a strong spark.
When the PCM detects an open circuit, short circuit, abnormal voltage, or improper ignition coil operation, it stores P0351 and illuminates the Check Engine Light.
The ignition system is responsible for:
- Producing spark
- Igniting the air/fuel mixture
- Maintaining engine performance
- Controlling emissions
- Supporting fuel economy
- Preventing engine misfires
- Protecting the catalytic converter
Common causes include:
- Failed ignition coil
- Damaged ignition coil connector
- Broken wiring
- Corroded terminals
- Shorted ignition coil circuit
- PCM driver failure (rare)
- Spark plug failure
- Excessive spark plug gap
Because ignition problems can quickly damage the catalytic converter, P0351 should be diagnosed and repaired as soon as possible.
What Does the P0351 Code Mean?
The ignition coil converts low battery voltage into the high-voltage spark required to ignite the air/fuel mixture inside the combustion chamber.
The PCM controls the ignition coil by switching the primary circuit on and off thousands of times per minute.
If the PCM detects that the ignition coil circuit is:
- Open
- Shorted
- Drawing excessive current
- Not responding properly
it stores P0351.
Unlike a simple misfire code, P0351 specifically identifies an electrical fault affecting the ignition coil circuit.
What Is an Ignition Coil?
Modern engines use Coil-on-Plug (COP) ignition systems or individual ignition coils instead of older distributor-based ignition systems.
Each ignition coil consists of:
- Primary winding
- Secondary winding
- Iron core
- Internal transistor (on some designs)
- Electrical connector
- Spark plug boot
The ignition coil transforms 12 volts from the battery into 20,000 to 60,000 volts, creating the spark that ignites the compressed air/fuel mixture.
Why the Ignition Coil Is Important
The ignition coil directly affects:
- Engine starting
- Engine power
- Fuel economy
- Idle quality
- Throttle response
- Emissions
- Catalytic converter protection
A weak or failed ignition coil can quickly cause engine misfires, rough operation, and increased exhaust emissions.
How the PCM Detects P0351
The PCM continuously monitors:
- Primary circuit voltage
- Coil current
- Driver circuit operation
- Ignition timing
- Engine RPM
- Crankshaft speed changes
- Misfire detection
If the ignition coil circuit does not respond as expected—or if an electrical fault is detected—the PCM stores P0351.
Some vehicles require multiple ignition events before the code is stored, while others illuminate the Check Engine Light almost immediately.
What Does “Primary/Secondary Circuit Malfunction” Mean?
P0351 does not automatically mean the ignition coil itself has failed.
Instead, it means the PCM has detected an electrical problem somewhere within the ignition coil circuit.
Possible causes include:
- Failed ignition coil
- Open circuit
- Short circuit
- Damaged wiring
- Loose connector
- Corroded terminals
- Faulty spark plug
- Damaged coil boot
- PCM driver failure (rare)
Proper diagnosis is essential before replacing ignition components.
Can a Bad Ignition Coil Cause P0351?
Absolutely.
A failed ignition coil is the most common cause of P0351.
Common ignition coil failures include:
- Internal winding failure
- Heat damage
- Moisture intrusion
- Cracked housing
- Electrical breakdown
- Internal short circuit
Many ignition coils fail intermittently before failing completely.
Can a Bad Spark Plug Cause P0351?
Yes.
Although P0351 is primarily an electrical circuit code, worn or damaged spark plugs can overload the ignition coil.
Common spark plug problems include:
- Excessive electrode gap
- Fouled plug
- Oil contamination
- Cracked ceramic insulator
- Incorrect heat range
A neglected spark plug can shorten ignition coil life.
Can Wiring Problems Cause P0351?
Definitely.
Inspect for:
- Broken wires
- Chafed insulation
- Loose connectors
- Corroded terminals
- Oil contamination
- Heat damage
Ignition wiring is frequently exposed to vibration and high engine temperatures.
P0351 Quick Facts
| Item | Information |
|---|---|
| DTC | P0351 |
| Generic Definition | Ignition Coil “A” Primary/Secondary Circuit Malfunction |
| System | Ignition System |
| Severity | High |
| Safe to Drive? | Limited driving only |
| Common Symptoms | Check Engine Light, misfire, rough idle, loss of power, hard starting |
| Common Causes | Failed ignition coil, damaged wiring, faulty spark plug, connector problems |
| Typical Repair Cost | $100–700+ |
| Related Codes | P0301, P0352, P0353, P0354, P0361 |
Common Vehicles That Experience P0351
P0351 commonly appears on:
- Chevrolet
- GMC
- Cadillac
- Buick
- Ford
- Lincoln
- Dodge
- Chrysler
- Jeep
- Ram
- Toyota
- Lexus
- Honda
- Acura
- Nissan
- Infiniti
- Hyundai
- Kia
- Subaru
- Volkswagen
It is especially common on:
- High-mileage engines
- Coil-on-plug ignition systems
- Turbocharged engines
- Engines with overdue spark plug maintenance
- Vehicles exposed to excessive engine heat
What Does P0351 Really Mean?
Many drivers assume P0351 automatically means the ignition coil must be replaced.
While the ignition coil is the most common cause, the PCM is actually reporting:
“An electrical problem exists in the Ignition Coil ‘A’ primary or secondary circuit. Inspect the ignition coil, spark plug, wiring, connectors, and PCM driver before replacing components.”
The underlying problem may involve:
- Ignition coil
- Spark plug
- Coil connector
- Wiring harness
- PCM driver circuit
- Ground circuit
- Coil boot
- Moisture intrusion
A complete diagnosis should always verify the entire ignition circuit before replacing parts.
Common P0351 Scan Tool Patterns
Using a professional scan tool is one of the fastest ways to diagnose P0351.
Because the PCM continuously monitors ignition coil operation, live scan data can quickly determine whether the fault is electrical, mechanical, or related to the ignition system.
Modern scan tools may display:
- Misfire Counters
- Engine RPM
- Ignition Timing
- Coil Command Status
- Short-Term Fuel Trim (STFT)
- Long-Term Fuel Trim (LTFT)
- Crankshaft Speed Variation
- Freeze-Frame Data
Monitoring these values often helps determine whether the problem originates with the ignition coil, spark plug, wiring, or PCM driver.
Pattern 1: P0351 with Cylinder 1 Misfire
One of the most common scan-tool patterns is:
- P0351 stored
- P0301 stored
- Misfire counter increasing on Cylinder 1
- Rough engine idle
Possible causes include:
- Failed ignition coil
- Faulty spark plug
- Coil connector failure
- Damaged wiring
This is the most common real-world scenario for P0351.
Pattern 2: P0351 Without a Misfire Code
Some vehicles display:
- Check Engine Light
- P0351 only
- Engine runs normally
- No noticeable drivability problems
Possible causes include:
- Intermittent coil failure
- Connector corrosion
- Wiring beginning to fail
- PCM detecting an electrical fault before a misfire develops
Early diagnosis often prevents more serious ignition problems.
Pattern 3: Misfire Only Under Load
Live data may show:
- Smooth idle
- Misfire during acceleration
- High engine load
- Increasing misfire counter
Possible causes include:
- Weak ignition coil
- Excessive spark plug gap
- High cylinder pressure
- Coil insulation breakdown
Many ignition coils fail only when cylinder pressure increases.
Pattern 4: Hard Starting
Some vehicles experience:
- Extended cranking
- Rough cold starts
- Engine shaking immediately after startup
- Misfires during warm-up
Possible causes include:
- Weak ignition coil
- Moisture inside the coil boot
- Damaged spark plug
- Low battery voltage
Cold-weather conditions often expose ignition coil failures.
Pattern 5: Intermittent Electrical Failure
Scan data may show:
- P0351 appears intermittently
- Misfire comes and goes
- Engine suddenly smooths out
- No consistent pattern
Possible causes include:
- Loose connector
- Broken wire
- Heat-related coil failure
- PCM driver issue (rare)
Heat cycling commonly causes intermittent electrical faults.
Pattern 6: Freeze-Frame During Heavy Acceleration
Freeze-frame data frequently shows:
- High engine load
- Moderate to high RPM
- Heavy throttle
- Sudden ignition failure
These operating conditions place the highest demand on the ignition system.
Pattern 7: Multiple Ignition Codes
P0351 may appear with:
- P0300
- P0301
- P0352
- P0353
- P0354
- P0316
Multiple ignition codes often indicate a larger electrical problem affecting the ignition system.
Common Symptoms of P0351
Symptoms vary depending on whether the ignition coil has failed completely or intermittently.
Common symptoms include:
- Check Engine Light
- Rough idle
- Engine misfire
- Loss of power
- Hard starting
- Poor acceleration
- Reduced fuel economy
- Increased exhaust emissions
- Engine hesitation
- Catalytic converter damage (if ignored)
Some vehicles may continue driving normally until the ignition coil fails completely.
Check Engine Light
The Check Engine Light is almost always the first symptom.
Many vehicles also store:
- P0301
- P0300
- Additional ignition coil circuit codes
Rough Idle
A failed ignition coil often causes:
- Engine shaking
- Rough idle
- Uneven RPM
- Engine vibration
The engine may smooth out temporarily as RPM increases.
Engine Misfire
A weak ignition coil cannot consistently ignite the air/fuel mixture.
Drivers may notice:
- Jerking
- Hesitation
- Bucking
- Engine stumbling
- Reduced engine performance
Persistent misfires can quickly damage the catalytic converter.
Loss of Power
When one cylinder loses spark:
Drivers often notice:
- Slow acceleration
- Reduced horsepower
- Poor throttle response
- Difficulty climbing hills
Turbocharged engines usually exhibit more severe power loss.
Poor Fuel Economy
Misfires prevent complete combustion.
The result is:
- Increased fuel consumption
- Rich exhaust mixture
- Reduced engine efficiency
- Increased emissions
Fuel economy often declines noticeably.
Is P0351 Serious?
Yes. P0351 is considered a high-severity diagnostic trouble code.
Although the vehicle may remain drivable, continued operation with an ignition fault may cause:
- Catalytic converter damage
- Severe engine misfires
- Increased fuel consumption
- Engine stalling
- Long-term ignition system damage
Repairs should be completed as soon as possible.
Can You Drive With P0351?
Limited driving may be possible, but it is not recommended.
Avoid driving if you experience:
- Severe engine misfire
- Flashing Check Engine Light
- Significant loss of power
- Engine stalling
- Strong fuel odor
- Rough running
A flashing Check Engine Light usually indicates active catalyst-damaging misfires.
P0351 vs Related Trouble Codes
Understanding related ignition system codes simplifies diagnosis.
P0351
Ignition Coil “A” Primary/Secondary Circuit Malfunction
General electrical malfunction affecting Ignition Coil “A.”
P0301
Cylinder 1 Misfire Detected
The PCM detects combustion failure on Cylinder 1.
P0352
Ignition Coil “B” Primary/Secondary Circuit Malfunction
Electrical fault affecting Ignition Coil “B.”
P0353
Ignition Coil “C” Primary/Secondary Circuit Malfunction
Electrical fault affecting Ignition Coil “C.”
P0354
Ignition Coil “D” Primary/Secondary Circuit Malfunction
Electrical fault affecting Ignition Coil “D.”
P0361
Ignition Coil “K” Primary/Secondary Circuit Malfunction
Electrical fault affecting another ignition coil circuit on engines with additional cylinders.
30 Common Causes of P0351
The most common causes include:
- Failed ignition coil
- Internal coil winding failure
- Excessive spark plug gap
- Worn spark plug
- Fouled spark plug
- Oil-contaminated spark plug
- Cracked ignition coil housing
- Damaged coil boot
- Moisture intrusion
- Open ignition coil circuit
- Shorted ignition circuit
- Broken wiring
- Chafed wiring harness
- Loose connector
- Corroded terminals
- Poor engine ground
- Weak battery voltage
- Charging system problems
- PCM driver circuit failure
- Aftermarket ignition components
- Incorrect spark plugs
- Engine overheating
- Oil leaking into spark plug wells
- Rodent-damaged wiring
- Water intrusion after engine washing
- Loose PCM connector
- Engine vibration damaging wiring
- Poor previous repairs
- Faulty PCM (rare)
- Internal engine mechanical problems causing excessive coil load
Final Thoughts
The P0351 Ignition Coil “A” Primary/Secondary Circuit Malfunction code indicates the PCM has detected an electrical problem affecting the ignition coil circuit—not necessarily a failed ignition coil itself.
Fortunately, failed ignition coils, worn spark plugs, damaged wiring, loose connectors, and oil contamination account for the vast majority of P0351 repairs.
Proper diagnosis should determine whether the fault originates in:
- Ignition coil
- Spark plug
- Coil connector
- Wiring harness
- Coil boot
- Ground circuit
- PCM driver
The next section of this guide covers:
- Complete diagnostic procedures
- Ignition coil testing
- Wiring diagnostics
- Spark plug inspection
- Repair procedures
- Repair costs
- Manufacturer-specific troubleshooting
Following a systematic diagnostic process prevents unnecessary parts replacement while restoring smooth engine operation, proper ignition performance, maximum fuel economy, and long-term engine reliability.
Related Pro Street Diagnostic Guides
- P0300 – Random/Multiple Cylinder Misfire Detected
- P0301 – Cylinder 1 Misfire Detected
- P0352 – Ignition Coil “B” Primary/Secondary Circuit Malfunction
- P0353 – Ignition Coil “C” Primary/Secondary Circuit Malfunction
- P0354 – Ignition Coil “D” Primary/Secondary Circuit Malfunction
- P0335 – Crankshaft Position Sensor “A” Circuit Malfunction
How to Diagnose the P0351 Code
Diagnosing P0351 requires determining why the Powertrain Control Module (PCM) has detected a malfunction in the Ignition Coil “A” Primary/Secondary Circuit.
Unlike a standard misfire code such as P0301, P0351 is an electrical circuit code, meaning the PCM has detected an abnormal condition affecting the ignition coil’s primary or secondary circuit.
The underlying problem may involve:
- Failed ignition coil
- Worn spark plug
- Excessive spark plug gap
- Damaged coil connector
- Broken wiring
- Corroded terminals
- Poor engine ground
- PCM driver failure (rare)
Because ignition faults can quickly damage the catalytic converter, P0351 should be diagnosed as soon as possible.
Safety Precautions
Before beginning diagnosis:
- Park on level ground.
- Apply the parking brake.
- Turn the ignition off.
- Allow the engine to cool.
- Wear safety glasses.
- Wear insulated gloves when working around ignition components.
Modern ignition coils can produce 20,000–60,000 volts. Never disconnect ignition components while the engine is running.
Tools Required
Professional diagnosis may require:
- Professional scan tool
- Digital multimeter
- Automotive oscilloscope
- Spark tester
- Manufacturer wiring diagrams
- Basic hand tools
- Battery load tester
- Dielectric grease
A dedicated spark tester is strongly recommended over using the spark plug itself.
Step 1 – Verify the Code
Connect a professional scan tool.
Record:
- Stored DTCs
- Pending DTCs
- Permanent DTCs
- Freeze-frame data
Monitor:
- Misfire counters
- Engine RPM
- Fuel trims
- Ignition timing
- Cylinder contribution
Never erase diagnostic codes before recording freeze-frame information.
Step 2 – Check for Related Trouble Codes
P0351 frequently appears with:
- P0300
- P0301
- P0352
- P0353
- P0354
- P0316
Related codes often help determine whether the problem involves only one ignition coil or the entire ignition system.
| Code Combination | Likely Diagnosis |
|---|---|
| P0351 only | Ignition coil circuit fault |
| P0351 + P0301 | Coil or spark plug failure on Cylinder 1 |
| P0351 + multiple P035X codes | Wiring or PCM issue |
| P0351 + P0300 | Multiple ignition system faults |
Step 3 – Review Freeze-Frame Data
Review:
- Engine RPM
- Engine load
- Coolant temperature
- Vehicle speed
- Battery voltage
- Throttle position
Determine whether the fault occurred:
- During startup
- Under heavy acceleration
- While idling
- During highway cruising
Freeze-frame data often reveals intermittent ignition failures.
Step 4 – Perform a Visual Inspection
Inspect the ignition coil.
Check for:
- Cracked housing
- Burn marks
- Oil contamination
- Water intrusion
- Loose mounting
- Damaged boot
Physical damage is often immediately visible.
Step 5 – Inspect the Wiring Harness
Follow the ignition coil wiring harness.
Inspect for:
- Broken wires
- Chafed insulation
- Heat damage
- Rodent damage
- Oil contamination
- Loose connectors
Repair damaged wiring before replacing ignition components.
Step 6 – Inspect the Electrical Connector
Disconnect the ignition coil connector.
Inspect for:
- Bent terminals
- Corrosion
- Moisture
- Loose terminal fit
- Broken locking tabs
Connector problems commonly trigger P0351.
Step 7 – Verify Battery and Charging System Voltage
Low battery voltage can affect ignition coil operation.
Normal voltage:
- Engine off: 12.4–12.8 volts
- Engine running: 13.5–14.8 volts
Correct charging system problems before continuing diagnosis.
Step 8 – Monitor Live Misfire Data
Using the scan tool:
Monitor:
- Misfire counters
- Cylinder contribution
- Engine RPM
- Fuel trims
Misfire activity concentrated on one cylinder strongly supports an ignition coil or spark plug problem.
Step 9 – Test the Ignition Coil
Remove the ignition coil.
Inspect for:
- Cracks
- Carbon tracking
- Burn marks
- Damaged boot
- Corrosion
Using manufacturer specifications:
Verify:
- Primary resistance
- Secondary resistance (if applicable)
- Coil output
Replace the coil if testing falls outside specifications.
Step 10 – Swap the Ignition Coil
One of the quickest diagnostic methods is to move the suspected ignition coil to another cylinder.
After swapping:
- Clear diagnostic codes.
- Drive the vehicle.
- Recheck for new codes.
If the fault changes from:
- P0351 → P0352
- P0301 → P0302
the ignition coil is defective.
This is one of the most reliable diagnostic techniques for coil-on-plug systems.
Step 11 – Inspect the Spark Plug
Remove the spark plug.
Inspect for:
- Excessive gap
- Oil fouling
- Carbon buildup
- Cracked ceramic
- Burned electrode
- Incorrect heat range
Replace worn spark plugs in complete sets whenever possible.
Step 12 – Test Power and Ground
Using a multimeter:
Verify:
- Battery voltage at the ignition coil
- Ground integrity
- PCM control signal
Repair any voltage or ground issues before replacing the PCM.
Step 13 – Inspect for Oil or Coolant Contamination
Oil leaking into spark plug wells commonly damages ignition coils.
Inspect for:
- Valve cover gasket leaks
- Oil contamination
- Coolant intrusion
- Moisture accumulation
Clean contaminated components before installing replacement coils.
Step 14 – Review Technical Service Bulletins
Before replacing expensive components:
Review manufacturer Technical Service Bulletins (TSBs).
Manufacturers occasionally release updates addressing:
- Ignition coil failures
- PCM software revisions
- Wiring harness repairs
- Connector improvements
Step 15 – Inspect the PCM Driver Circuit
If the ignition coil, spark plug, and wiring all test normally:
Inspect:
- PCM driver signal
- Control wire continuity
- Driver pulse using an oscilloscope
PCM driver failures are uncommon but possible.
Step 16 – Perform a Road Test
Monitor live scan tool data while driving.
Observe:
- Misfire counters
- Ignition timing
- Engine RPM
- Fuel trims
Attempt to duplicate the operating conditions recorded in freeze-frame data.
Step 17 – Verify Operation at Normal Temperature
Many ignition coils fail only after heating up.
Allow the engine to reach operating temperature.
Continue monitoring:
- Misfire counts
- Coil operation
- Engine performance
Heat-related failures frequently appear after 15–30 minutes of driving.
Step 18 – Inspect Catalytic Converter Protection
If severe misfires have occurred:
Inspect for:
- Flashing Check Engine Light history
- Sulfur odor
- Converter overheating
- Excessive exhaust temperatures
Extended driving with P0351 may damage the catalytic converter.
Step 19 – Complete an OBD-II Drive Cycle
After repairs:
- Clear diagnostic codes.
- Complete the manufacturer’s drive cycle.
- Verify readiness monitors complete.
- Confirm P0351 does not return.
Step 20 – Confirm the Diagnosis
Before replacing expensive components, verify:
- Ignition coil condition
- Spark plug condition
- Coil connector integrity
- Wiring harness
- Battery voltage
- Engine grounds
- PCM control signal
- PCM software version
Completing these diagnostic procedures prevents unnecessary parts replacement while accurately identifying the root cause of P0351.
Step 21 – Replace the Ignition Coil
If testing confirms Ignition Coil “A” has failed, replacement is the proper repair.
Common signs of ignition coil failure include:
- P0351 immediately returns after clearing
- Cylinder 1 misfire
- Rough idle
- Engine hesitation
- Hard starting
- Loss of power
- Flashing Check Engine Light
General replacement procedure:
- Disconnect the negative battery cable.
- Remove any engine covers.
- Disconnect the ignition coil electrical connector.
- Remove the coil retaining bolt.
- Pull the ignition coil straight upward.
- Inspect the spark plug well for oil or coolant contamination.
- Install the new OEM-quality ignition coil.
- Apply dielectric grease to the coil boot if recommended.
- Reconnect the electrical connector.
- Clear diagnostic trouble codes.
Whenever possible, install OEM or premium aftermarket ignition coils to ensure proper spark energy and reliability.
Step 22 – Replace the Spark Plug
A worn spark plug often contributes to ignition coil failure.
Inspect the spark plug for:
- Excessive electrode gap
- Carbon buildup
- Oil fouling
- Cracked porcelain
- Burned electrodes
- Incorrect heat range
Replace spark plugs according to manufacturer specifications.
Many technicians recommend replacing the spark plug whenever an ignition coil has failed to prevent premature failure of the new coil.
Step 23 – Repair Wiring Problems
Inspect the complete ignition coil wiring harness.
Look for:
- Broken wires
- Chafed insulation
- Heat damage
- Oil contamination
- Rodent damage
- Loose terminals
Repair wiring using:
- Soldered wire repairs
- Heat-shrink tubing
- OEM-style connectors
- Proper wire routing
Many intermittent P0351 faults are caused by damaged wiring rather than the ignition coil itself.
Step 24 – Repair or Replace Electrical Connectors
Inspect the ignition coil connector for:
- Bent terminals
- Corrosion
- Burned contacts
- Loose pins
- Broken locking tabs
- Moisture intrusion
Replace damaged connectors using OEM repair kits whenever possible.
Poor electrical contact frequently causes intermittent ignition coil operation.
Step 25 – Repair Oil Leaks
Oil contamination is a common cause of ignition coil failure.
Inspect for:
- Valve cover gasket leaks
- Spark plug tube seal leaks
- Oil pooling in spark plug wells
Repair oil leaks before installing replacement ignition components.
Failure to correct oil leaks often results in repeated ignition coil failures.
Step 26 – Repair Engine Ground Problems
Verify all engine grounds are clean and secure.
Inspect:
- Battery grounds
- Engine block grounds
- Cylinder head grounds
- PCM grounds
Poor grounding can interfere with ignition coil operation and trigger intermittent circuit faults.
Step 27 – Repair PCM Driver Circuit (If Necessary)
If testing confirms the ignition coil, spark plug, connector, wiring, and grounds are all functioning correctly:
Inspect:
- PCM control signal
- Driver transistor output
- Control circuit continuity
PCM driver failures are uncommon and should only be diagnosed after every other component has been verified.
Step 28 – Update PCM Software
Before replacing the PCM:
Review manufacturer Technical Service Bulletins (TSBs).
Manufacturers occasionally release software updates addressing:
- False ignition coil fault detection
- Ignition timing improvements
- Misfire detection calibration
- PCM software revisions
Always install the latest available calibration whenever applicable.
Step 29 – Complete an OBD-II Drive Cycle
After repairs:
- Clear all diagnostic trouble codes.
- Start the engine.
- Allow the engine to reach operating temperature.
- Complete the manufacturer’s drive cycle.
- Verify readiness monitors complete successfully.
Confirm P0351 does not return.
Step 30 – Verify the Repair
After completing repairs:
- Clear all stored diagnostic codes.
- Start the engine.
- Verify a smooth idle.
- Road test the vehicle.
- Monitor live misfire data.
- Confirm ignition timing remains stable.
- Verify no pending or permanent DTCs return.
- Ensure the Check Engine Light remains off.
A successful repair restores smooth engine operation, proper ignition performance, full engine power, and maximum fuel economy.
How to Fix P0351
The correct repair depends on the diagnostic results.
Common repairs include:
- Replacing the ignition coil
- Replacing worn spark plugs
- Repairing damaged wiring
- Replacing electrical connectors
- Repairing engine ground connections
- Repairing valve cover oil leaks
- Updating PCM software
- Replacing the PCM (rare)
Never replace the PCM until every ignition component and electrical circuit has been thoroughly tested.
Typical Repair Costs
| Repair | Typical Cost |
|---|---|
| Professional diagnosis | $100–250 |
| Ignition coil replacement | $125–350 |
| Spark plug replacement | $150–450 |
| Ignition coil connector replacement | $100–250 |
| Wiring repair | $100–350 |
| Valve cover gasket replacement | $200–600 |
| Engine ground repair | $75–200 |
| PCM software update | $100–250 |
| PCM replacement (rare) | $800–2,000+ |
Repair costs vary depending on engine design, labor rates, and ignition system accessibility.
Common Diagnostic Mistakes
Avoid these common mistakes:
- Replacing the ignition coil without testing the spark plug
- Ignoring oil contamination in the spark plug well
- Skipping wiring inspections
- Overlooking damaged electrical connectors
- Ignoring battery voltage and engine grounds
- Clearing codes before recording freeze-frame data
- Replacing the PCM without verifying the driver circuit
- Installing low-quality aftermarket ignition coils
Many P0351 repairs involve worn spark plugs or damaged wiring rather than PCM failure.
Manufacturer-Specific Notes
General Motors (Chevrolet, GMC, Cadillac, Buick)
Inspect:
- Coil-on-plug ignition coils
- Valve cover oil leaks
- Coil connectors
- Engine grounds
GM V8 engines commonly experience ignition coil failures as mileage increases.
Ford/Lincoln
Inspect:
- COP ignition coils
- Spark plug condition
- Coil boots
- Moisture intrusion
Many Ford engines experience intermittent coil failures under heavy engine load.
Chrysler, Dodge, Jeep, Ram
Inspect:
- Ignition coil connectors
- PCM driver circuits
- Wiring near exhaust manifolds
- Spark plug wells
Heat-related wiring damage is relatively common.
Toyota/Lexus
Inspect:
- Denso ignition coils
- Spark plug tube seals
- Coil connectors
- Valve cover gasket leaks
Oil contamination is a frequent contributor to repeated coil failures.
Nissan/Infiniti
Inspect:
- Ignition coil boots
- Spark plug wells
- Wiring harness
- Ground circuits
Several Nissan V6 engines are known for age-related ignition coil failures.
Honda/Acura
Inspect:
- Coil-on-plug assemblies
- Valve adjustment history
- Spark plugs
- Oil contamination
Using OEM ignition components generally provides the best long-term reliability.
Frequently Asked Questions
What usually fixes P0351?
The most common repairs include replacing a failed ignition coil, replacing worn spark plugs, repairing damaged wiring, replacing faulty electrical connectors, repairing oil leaks into the spark plug wells, or correcting poor ground connections.
Can I drive with P0351?
Limited driving may be possible, but repairs should be completed immediately. Driving with an active ignition fault can cause severe engine misfires, poor performance, increased fuel consumption, and catalytic converter damage.
Does P0351 always mean the ignition coil is bad?
No. Although the ignition coil is the most common cause, P0351 may also result from damaged wiring, faulty connectors, worn spark plugs, poor engine grounds, or a failed PCM driver.
Can a bad spark plug cause P0351?
Yes. An excessively worn or improperly gapped spark plug forces the ignition coil to generate higher voltage, increasing stress on the ignition system and potentially triggering P0351.
Is P0351 a serious code?
Yes. P0351 is considered a high-severity diagnostic trouble code. Ignoring the problem can lead to catalytic converter damage, severe engine misfires, reduced fuel economy, increased emissions, and poor overall engine performance.
Final Thoughts
The P0351 Ignition Coil “A” Primary/Secondary Circuit Malfunction code indicates the PCM has detected an electrical fault affecting the ignition system. While the ignition coil is the most common culprit, the fault may also originate from worn spark plugs, damaged wiring, poor electrical connections, oil contamination, or PCM driver issues.
Fortunately, ignition coil failures, spark plug wear, damaged connectors, wiring faults, and oil leaks account for the vast majority of P0351 repairs.
A complete diagnosis should always verify:
- Ignition coil condition
- Spark plug condition
- Coil connector integrity
- Wiring harness
- Engine grounds
- Battery voltage
- PCM control signal
- PCM software version
Following a systematic diagnostic process prevents unnecessary parts replacement while restoring smooth engine performance, reliable ignition operation, maximum fuel economy, and long-term engine reliability.
Continue Your Pro Street Ignition System Series
Related guides include:
- P0300 – Random/Multiple Cylinder Misfire Detected
- P0301 – Cylinder 1 Misfire Detected
- P0352 – Ignition Coil “B” Primary/Secondary Circuit Malfunction
- P0353 – Ignition Coil “C” Primary/Secondary Circuit Malfunction
- P0354 – Ignition Coil “D” Primary/Secondary Circuit Malfunction
- P0335 – Crankshaft Position Sensor “A” Circuit Malfunction
