P1365
FordIgnition Coil Secondary Circuit Failure
The engine computer has detected a fault in the ignition coil’s secondary circuit, which delivers high voltage to fire the spark plug. The fault can cause weak or missing spark, but the code alone does not prove the coil itself has failed. Exact system design and diagnostic procedures depend on the vehicle’s model, year, and engine.
⚠️ Before You Begin (Safety First)
A severe misfire can cause loss of power and may damage the catalytic converter. If the check-engine light is flashing, the engine is shaking badly, or power is reduced enough to make driving unsafe, stop driving when safe and arrange diagnosis. Do not handle ignition components while the engine is running; the secondary circuit carries high voltage.
Common Symptoms
- Engine misfire, rough running, or shaking if spark is weak or missing.
- Reduced power or hesitation if combustion is affected.
- Check-engine light; it may flash during a severe misfire.
- Hard starting or stalling may occur if the fault significantly disrupts ignition.
- There may be no noticeable symptoms if the fault is intermittent or limited.
Common Causes
- Ignition coil secondary insulation or output fault.
- Damaged, worn, or incorrectly functioning spark plug.
- Damaged plug wire or coil boot, where the vehicle uses one.
- Poor connection, corrosion, moisture, or contamination in a secondary ignition connection.
- A wiring or control-side fault affecting ignition operation; diagnosis is needed to distinguish this from a secondary-component fault.
Diagnostic Steps
- Record the code and any other stored codes before clearing anything; related codes and operating data can help identify when the fault occurs.
- With the engine off and cool, visually inspect accessible ignition components for cracked insulation, damaged boots or wires, loose connections, moisture, or signs of arcing.
- Check the applicable spark plugs for visible damage or heavy deposits only if you can remove and reinstall them safely and correctly for your engine.
- Do not touch or disconnect ignition components with the engine running, and do not probe high-voltage ignition circuits.
- If inspection does not reveal an obvious issue, have the circuit tested using vehicle-specific service information and suitable equipment.
When to Call a Professional
Confirm the code and review freeze-frame data and available misfire information. Inspect the applicable coil, secondary connections, spark plugs, and any plug wires or boots for damage, carbon tracking, moisture, or poor contact. Use model-, year-, and engine-specific service information to test the circuit; avoid relying on the code alone to justify replacing the coil.
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Commonly Asked Questions
Does P1365 prove the ignition coil is bad?
No. The code identifies a detected secondary-circuit fault, not a confirmed failed part. A plug, wire or boot where fitted, connection, or other circuit fault can also be involved.
Can I keep driving with this code?
A mild or intermittent fault may not immediately make the vehicle unsafe, but a severe misfire can reduce power and damage the catalytic converter. Stop when safe if the check-engine light is flashing or the engine is running very roughly.
Why might there be no symptoms?
The fault may be intermittent or may not be affecting combustion noticeably at the time. Stored code data and a proper circuit inspection can help establish whether the condition is still present.
What should be checked before replacing a coil?
Check the relevant secondary connections, spark plug, and any wire or boot used by the vehicle, then test the circuit using service information for the exact model, year, and engine.
Browse Available Code Guides
Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.