Ignition Coil Primary Control Circuit Low
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 switching of the coil to generate spark. A low voltage reading suggests excessive resistance, a short to ground, or a faulty coil driver, leading to weak or no spark in that cylinder.
1. Most Common Causes
- Ignition coil 'G' has an internal short in the primary winding
- Control circuit (driver) wiring shorted to ground (chassis)
- Damaged coil connector with bent pins or corrosion causing a ground short
- Faulty ignition driver (Darlington transistor/MOSFET) inside the PCM
- Poor connection at the PCM connector (loose or backed-out pin)
2. Symptoms You Will Notice
- Engine misfire
- Check Engine Light on
- Rough idle
- Decreased fuel economy
- Engine hesitation or lack of power
3. Step-by-Step Diagnosis
Step 1: Scan for codes and note which cylinder is affected.
Step 2: Visually inspect the ignition coil and wiring for damage, corrosion, or loose connections.
Step 3: Use a multimeter to check the primary coil resistance (specs vary, typically 0.5-2 ohms).
Step 4: Check for voltage and ground at the coil connector with the ignition on.
Step 5: Swap the suspect coil with another cylinder and see if the code moves; if so, replace the coil.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code as it can cause engine misfire, reduced performance, and potential damage to the catalytic converter.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for a DIY replacement of the ignition coil, or $100 to $250 if done by a shop including labor.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.