Ignition Coil Primary Circuit Low Voltage
The P2318 code indicates that the powertrain control module (PCM) has detected a low voltage condition in the primary control circuit of a specific ignition coil. This circuit controls the coil's ground path to fire the spark plug. A low voltage reading suggests excessive resistance, a short to ground, or a failing coil driver. This can cause weak or no spark, leading to misfires and poor engine performance.
01. Most Common Causes
- Faulty ignition coil
- Open or shorted wiring in the primary control circuit
- Poor electrical connection at the coil or PCM
- Failed PCM (rare)
02. Symptoms You Will Notice
- Engine misfire or rough idle
- Check Engine Light illuminated
- Reduced engine power and acceleration
- Increased fuel consumption
03. Step-by-Step Diagnosis
Step 1: Scan for codes and note which cylinder is affected.
Step 2: Visually inspect the ignition coil connector and wiring for damage or corrosion.
Step 3: Measure resistance of the primary coil circuit (typically 0.5-2 ohms).
Step 4: Check for battery voltage and ground at the coil connector with key on.
Step 5: Swap the suspect coil with another cylinder and see if the code moves.
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 cause poor drivability.
How much does it cost to fix?▼
Typically $50-$150 for a DIY coil replacement, or $150-$300 at a shop including diagnosis.