OBD Code P0355: Ignition Coil D Primary/Secondary Circuit Malfunction

Q: What does OBD code P0355 mean?

Ignition Coil D Primary/Secondary Circuit Malfunction. Coil D (usually cylinder 4) isn't firing correctly—the ECU detects an electrical problem in the ignition coil circuit. Think of it like a spark plug wire with a loose connection that won't reliably deliver power.

Q: What are the symptoms of fault code P0355?

Rough idle or misfiring on cylinder 4, Check Engine Light illuminated, Reduced fuel economy and power loss

Q: How do I fix OBD fault code P0355?

Inspect connector pins for corrosion, bent terminals, or loose fit; clean with electrical contact cleaner and reseat firmly.. Remove and test coil resistance with a multimeter; replace if out of spec or visibly cracked.. Remove spark plug and inspect for fouling; replace both plug and boot if degraded or damaged.

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What This Actually Means

In plain language — no jargon

Coil D (usually cylinder 4) isn't firing correctly—the ECU detects an electrical problem in the ignition coil circuit. Think of it like a spark plug wire with a loose connection that won't reliably deliver power.

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Symptoms You May Notice

3 known symptoms for this code

Rough idle or misfiring on cylinder 4

Check Engine Light illuminated

Reduced fuel economy and power loss

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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors the primary coil winding resistance and the secondary voltage output during ignition events. It detects abnormal current draw, open circuits, or shorts in the coil D circuit. If resistance or voltage falls outside acceptable ranges, the fault triggers.

Voltage & Parameter Thresholds

Parameter	Normal Range	Fault Condition
Primary Coil Resistance	0.4–2 ohms	< 0.2 ohms or > 3 ohms
Ignition Output Voltage	> 8 kV under load	< 6 kV or no voltage detected

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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex

1

Ignition coil connector and harness

Inspect connector pins for corrosion, bent terminals, or loose fit; clean with electrical contact cleaner and reseat firmly.

2

Ignition coil D

Remove and test coil resistance with a multimeter; replace if out of spec or visibly cracked.

3

Spark plug and wire/coil-on-plug boot

Remove spark plug and inspect for fouling; replace both plug and boot if degraded or damaged.

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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0355 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.

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How to Clear Code P0355

What happens after you fix the fault

Once the fault is repaired, P0355 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When

Fault has been diagnosed and repaired
You want to confirm the repair worked
Code appeared after a sensor was cleaned

⚠️ Do Not Clear When

Preparing for an emissions/PUC test
Root cause is still undiagnosed
Check engine light is flashing

Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.