P0351: Ignition coil A primary or secondary circuit fault

Ignition coil A circuit

Severity: Inspect soon

P0351 means the engine computer saw a fault in the circuit for ignition coil A. That coil's cylinder may misfire, which wastes fuel and can overheat the catalytic converter, and on some cars it causes hard starting or a no-start. Get it inspected soon.

It gets more serious if:

Stop: The check engine light is flashing. That means misfire bad enough to damage the catalytic converter is happening right now; Ford warns the extra exhaust heat can damage the converter and nearby parts and could cause a fire. Pull over when safe and avoid further driving, or at most drive gently and slowly to the nearest shop (EPA's own advice is to minimise driving and avoid speed and heavy loads).
Stop: The engine stalls, cuts out while driving, or cranks but will not start. A crank or cam sensor signal that drops out can shut the engine off without warning, and Toyota recalled a crank sensor fault that could stall the engine because a stall at higher speeds may increase the risk of a crash. Do not keep driving; have it towed or checked where it sits.

Source: how we rate severity

P0351 in short

P0351 means the engine computer detected a problem in the circuit for ignition coil A. Inspect the coil, its connector and the spark plug well first, then test the coil and its wiring. Expect a misfire on that cylinder. Get it inspected soon, and stop driving if the light flashes.

Each ignition coil turns battery voltage into the high voltage that fires a spark plug. The engine computer switches the coil on and off and watches the circuit; P0351 sets when coil A's circuit does not behave as expected.

Which cylinder coil A serves depends on the engine, so check the service information. A coil that stops working causes a misfire on its cylinder, and unburned fuel from a misfire can overheat the catalytic converter.

Worn plugs and oil or water in the plug well are common reasons coils fail, so fix those too or the new coil may fail again.

Most likely causes

Cause 1: Failed ignition coil A
Common general cause
Why it ranks here
Coils break down from heat, vibration and moisture, and an open or shorted winding is the most direct way to set a coil circuit code.
What would change this
Rises if the coil's resistance is out of specification or it is cracked, carbon-tracked or oil-soaked; falls if it measures good and the code follows the wiring rather than the coil.
How to test the ignition coil
Cause 2: Coil supply, ground or control wiring or connector fault
Common general cause
Why it ranks here
The coil needs battery voltage and a control signal from the engine computer, whose coil drivers sit inside it on a typical design. A loose connector or damaged wire looks the same to the computer as a failed coil.
What would change this
Rises if supply voltage is low with the ignition on (Delphi gives above 10.5 V as typical) or the connector is loose or corroded.
How to test the ignition coil
Cause 3: Worn spark plug or oil/water in the plug well damaging the coil
Common general cause
Why it ranks here
A worn plug raises the voltage the coil must produce, and oil from a leaking valve cover gasket or water in the plug well breaks down coil insulation. These are why coils fail, and a new coil fails again if they are ignored.
What would change this
Rises with an overdue plug change, a worn plug gap, or oil or water found in the plug well.
How to test the spark plug
Cause 4: Engine computer software or logic (some models)
Supported by vehicle data
Why it ranks here
Toyota improved the engine computer logic for P0351-P0354 on the 2007 Camry, so on listed vehicles a software update can be the fix.
What would change this
Rises if a bulletin for your vehicle covers the code and the update has not been done.
Cause 5: Damaged crank trigger causing coil faults (2015-2016 Fiesta 1.6L)
Supported by vehicle data
Why it ranks here
Ford found that a damaged or warped Hall-effect window on the flywheel could set P0351/P0352 with rough running or a no-start on 2015-2016 Fiesta 1.6L engines.
What would change this
Applies only to the listed vehicles; rises if the coil control signal is inconsistent during Ford's pinpoint test.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

Step 1: With the engine off, remove the cover if needed and inspect coil A and its connector: look for cracks, carbon tracks, a loose or corroded connector, and oil or water in the plug well.
Low riskTool: flashlight, service information for which coil is A
- IfOil or water in the well, or a worn plug
  It meansFix the leak and plug as well as the coil.
  Points to: Worn spark plug or oil/water in the plug well damaging the coil
- IfCracked, burned or tracked coil
  It meansThe coil is damaged.
  Points to: Failed ignition coil A
- IfEverything looks good
  It meansTest the circuit.
  Go to step 2
Step 2: Unplug the coil and, with the ignition on and the engine off, measure the supply voltage at the harness connector.
Use cautionTool: digital multimeter, wiring diagram
Warning:Keep the engine off. Do not crank the engine with a coil unplugged or probe the coil while the engine runs; ignition voltage can cause a serious shock.
- IfSupply is low or missing
  It meansA wiring, fuse or relay problem.
  Points to: Coil supply, ground or control wiring or connector fault
- IfSupply is normal
  It meansCheck the coil itself.
  Go to step 3
Step 3: With the ignition off, measure the coil's resistance and compare with the vehicle's specification.
Use cautionTool: digital multimeter, service information
Warning:Ignition off before touching coil terminals.
- IfOut of specification
  It meansThe coil has failed.
  Points to: Failed ignition coil A
- IfIn specification
  It meansThe fault is in the control circuit or software.
  Go to step 4
Step 4: Have a shop check the coil control signal from the engine computer and look for bulletins or software updates for your vehicle.
Best left to a shopTool: lab scope, service information
Warning:Checks with the engine running involve high ignition voltage and moving parts. Leave this to a shop.
- IfControl wire open or shorted
  It meansRepair the wiring.
  Points to: Coil supply, ground or control wiring or connector fault
- IfA bulletin or update covers the code
  It meansFollow the bulletin.
  Points to: Engine computer software or logic (some models)
- IfInconsistent control signal on a listed Fiesta
  It meansFord's bulletin points to the flywheel trigger.
  Points to: Damaged crank trigger causing coil faults (2015-2016 Fiesta 1.6L)

Symptoms

Rough running or misfire
Reduced power
Hard starting or no start Gets more serious: stop and have it checked.
Check engine light flashing Gets more serious: stop and have it checked.

Compare with: Rough idle with the check engine light on, Car shaking with the check engine light on

How to fix

Step 1: Write down every stored code and the freeze-frame data before clearing anything, so you can tell whether the code comes back.
Step 2: If the plugs are due by the maintenance schedule, have them replaced along with any failed coil.
Warning:Only remove coils and plugs with the engine off and cool, and tighten plugs to the specified torque.

On your vehicle

Ford

2015–2016 · Fiesta · 1.6L Ti-VCT
Supported by vehicle data
On the 1.6L Ti-VCT, Ford links P0351/P0352 with rough running or a no-start to a damaged flywheel trigger window. Ask a dealer to check SSM 45988 before replacing coils.
2006–2008 · Fusion
Supported by vehicle data
Ford has a bulletin for coil circuit codes with damaged coil-on-plug units on this model. Ask a dealer to check TSB 13-4-17.
2007–2008 · Edge
Supported by vehicle data
Ford has a bulletin for coil circuit codes with damaged coil-on-plug units on this model. Ask a dealer to check TSB 13-4-17.
2008 · Taurus
Supported by vehicle data
Ford has a bulletin for coil circuit codes with damaged coil-on-plug units on this model. Ask a dealer to check TSB 13-4-17.

SSM 45988Status unverified
Ford SSM 45988: P0351/P0352 with rough running, hard or no start
2015–2016fiesta · 1.6L Ti-VCT · issued August 11, 2016 · NHTSA 10092410
On 2015-2016 Fiesta with the 1.6L Ti-VCT engine, if the test light flash is inconsistent or dim during the coil pinpoint test, suspect a damaged or warped Hall-effect window on the flywheel and replace the flywheel.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
TSB 13-4-17Status unverified
Ford TSB 13-4-17: P0351-P0355 with coil-on-plug damage
2006–2008fusion, edge, taurus · issued April 24, 2013 · NHTSA 10052190
Covers ignition coil circuit codes with one or more damaged coil-on-plug units on 2006-2008 Fusion, Milan, MKZ and Zephyr, 2007-2008 Edge and MKX, and 2008 Taurus and Sable. NHTSA's summary does not give the repair.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Toyota

2007 · Camry
Supported by vehicle data
Toyota addresses P0351-P0354 on this model with improved engine computer logic. Ask a dealer whether the update applies before replacing coils.

TSB-0101-09Status unverified
Toyota TSB-0101-09: MIL with P0351-P0354, improved ECM logic
2007camry · issued April 6, 2009 · NHTSA 10030327
Ignition coil circuit codes P0351-P0354 on the 2007 Camry (NHTSA lists the Camry Hybrid) are addressed by improved engine computer logic.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

All Ignition and engine position sensors codes

P0351 questions

Which cylinder is ignition coil A?

It depends on the engine, so confirm it in the service information for your vehicle before replacing anything. P0351, P0352, P0353 and so on each cover one coil (A, B, C and so on).

Can I drive with a flashing check engine light?

Not if you can avoid it. A flashing light means misfire severe enough to overheat the catalytic converter is happening now. Ford's owner guide warns the heat can damage the converter and could start a fire; EPA advises keeping driving to a minimum. Drive gently to the nearest shop at most, or have it towed.

Should I replace the spark plug with the coil?

If the plug is worn or due for replacement, yes. A worn plug makes the coil work harder, and both DENSO and Delphi name worn plugs as a cause of coil failure.

Sources and review

How to service ignition coils — Delphi Technologies Aftermarket
What You Should Know About Catalytic Converters — AA1Car.com (Larry Carley, automotive technical writer)
Ford SSM 45988: P0351/P0352 with rough running, hard or no start, 2015-2016 Fiesta 1.6L — Ford Motor Company (via NHTSA) , August 11, 2016
Cal. Code Regs. tit. 13, § 1968.2 - Malfunction and Diagnostic System Requirements (OBD II) — California Air Resources Board (via Cornell LII)
2001 Lincoln Continental Owner's Guide - Warning lights (Check engine) — Ford Motor Company
Do you drive a 1996 or newer car or light truck? (On-Board Diagnostics, EPA420-F-02-016) — U.S. Environmental Protection Agency
Safety Recall H0H Remedy Notice: Certain 2016-2017 Model Year Tacoma Crankshaft Position Sensor, Frequently Asked Questions — Toyota Motor North America , July 24, 2017
Toyota Recalls Tacoma Pickups for Stalling — Automotive Fleet , June 9, 2017
Causes of ignition coil failure — DENSO Aftermarket Europe , January 16, 2024
ASE L1 Advanced Engine Performance Specialist Test: Composite Vehicle Type 4 Reference Booklet — National Institute for Automotive Service Excellence (ASE)
Ford TSB 13-4-17: P0351-P0355 with coil-on-plug damage — Ford Motor Company (via NHTSA) , April 24, 2013
Toyota TSB-0101-09: MIL with P0351-P0354 - improved ECM logic — Toyota Motor Sales (via NHTSA) , April 6, 2009
How To Diagnose & Repair Engine Misfires — AA1Car.com (Larry Carley, automotive technical writer)

Last reviewed: October 15, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

Severity: Inspect soon

Most likely causes

Cause 1: Failed ignition coil A

Cause 2: Coil supply, ground or control wiring or connector fault

Cause 3: Worn spark plug or oil/water in the plug well damaging the coil

Cause 4: Engine computer software or logic (some models)

Cause 5: Damaged crank trigger causing coil faults (2015-2016 Fiesta 1.6L)

What to test first

Step 1: With the engine off, remove the cover if needed and inspect coil A and its connector: look for cracks, carbon tracks, a loose or corroded connector, and oil or water in the plug well.

Step 2: Unplug the coil and, with the ignition on and the engine off, measure the supply voltage at the harness connector.

Step 3: With the ignition off, measure the coil's resistance and compare with the vehicle's specification.

Step 4: Have a shop check the coil control signal from the engine computer and look for bulletins or software updates for your vehicle.