Ignition Coil A Primary/Secondary Circuit Malfunction
The P0351 code indicates a malfunction in the primary or secondary circuit of ignition coil 'A' (typically coil #1). The Powertrain Control Module (PCM) monitors the voltage and current in the coil's primary circuit. When the PCM detects an abnormal voltage drop, open circuit, short, or excessive resistance, it sets this code. This can cause misfires, reduced engine performance, and increased emissions.
01. Most Common Causes
- Faulty ignition coil
- Open or shorted wiring in the coil circuit
- Poor electrical connection at the coil connector
- Failed PCM (rare)
02. Symptoms You Will Notice
- Engine misfire (especially under load)
- Check Engine Light illuminated
- Rough idle or hesitation during acceleration
- Decreased fuel economy
03. Step-by-Step Diagnosis
Step 1: Scan for codes and verify P0351 is present. Check for other related codes (e.g., misfire codes).
Step 2: Visually inspect the ignition coil and its wiring for damage, corrosion, or loose connections.
Step 3: Swap the suspect coil with another cylinder. If the code moves to the new cylinder, replace the coil.
Step 4: Test the coil's primary and secondary resistance with a multimeter and compare to manufacturer specs.
Step 5: Check for power and ground at the coil connector with the ignition on. If missing, repair wiring or replace PCM.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a misfire can damage the catalytic converter and reduce fuel economy. Have it diagnosed promptly.
How much does it cost to fix?▼
Replacing an ignition coil typically costs $50-$150 for parts and labor, depending on vehicle make and model.