What Does P0351 Mean?
The ECM has detected a malfunction in the primary or secondary circuit of ignition coil A, which typically serves cylinder #1. This indicates the ECM's coil driver cannot properly control the coil, or the coil's primary or secondary windings have failed. The affected cylinder will misfire continuously, causing rough running, increased emissions, and a flashing MIL if the misfire rate is high enough to damage the catalytic converter.
Common Causes
40%
Failed coil-on-plug (COP) ignition coil A with cracked internal winding insulation or burned primary circuit from overheating
25%
Open or short in the coil A control wire between the ECM coil driver and the coil primary trigger terminal
20%
Fouled or worn spark plug causing excessive secondary circuit demand leading to coil feedback and driver fault detection
15%
ECM internal ignition coil driver transistor failure for the cylinder 1 output
Diagnostic Steps
1
Swap ignition coil A with an adjacent cylinder's coil and clear codes. If the P0351 follows the coil to the new position (e.g., changes to P0352), the coil has failed and needs replacement.
2
Measure coil A primary resistance (typically 0.4-1.0 ohms) and secondary resistance (typically 6,000-12,000 ohms). Readings outside specification or open/short circuits confirm coil failure.
3
With the coil connector disconnected, verify the ECM sends a proper trigger signal during cranking using an oscilloscope or noid light on the coil driver wire. No signal indicates ECM driver failure or wiring issue.
4
Remove and inspect the cylinder 1 spark plug for fouling, excessive wear (gap exceeding 0.060"), or cracked insulator. A badly worn plug forces the coil to produce excessive voltage, accelerating coil failure.
5
Check for battery voltage at the coil A power supply pin with KOEO. Verify less than 0.5V drop across the power feed circuit under load.
Estimated Repair Cost
$60 - $300
Parts + labor, varies by vehicle and location
The ECM has detected a malfunction in the primary or secondary circuit of ignition coil A, which typically serves cylinder #1. This indicates the ECM's coil driver cannot properly control the coil, or the coil's primary or secondary windings have failed. The affected cylinder will misfire continuous...
The most common cause of P0351 (Ignition Coil A Primary/Secondary Circuit Malfunction) is: Failed coil-on-plug (COP) ignition coil A with cracked internal winding insulation or burned primary circuit from overheating
Typical repair costs for P0351 range from $60 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A dead cylinder from coil A failure reduces engine power and can cause hesitation during acceleration. Prolonged driving with a misfiring cylinder risks catalytic converter overheating and potential failure.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0351 to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
