P1370 Ignition Coil Secondary Circuit Malfunction
The P1370 code indicates a fault in the ignition coil secondary circuit, specifically in Ford vehicles equipped with Capacitor Discharge Ignition (CDI) or Coil-on-Plug (COP) systems. The secondary circuit carries high voltage from the coil to the spark plugs. The Powertrain Control Module (PCM) detects that the voltage or current in this circuit is not within expected values during the ignition event, which may point to a failing coil, poor connections, or high-voltage wiring issues.
01. Most Common Causes
- Faulty or deteriorated ignition coil
- Short circuit or open circuit in the secondary circuit wiring
- Corroded or loose connectors in the coil circuit
- Worn, incorrect heat range, or damaged spark plugs
- Faulty Ignition Control Module (ICM) or PCM
- Excessive resistance in spark plug wires (if applicable)
02. Symptoms You Will Notice
- Engine misfire or rough idle
- Check Engine Light illuminated
- Reduced engine power or hesitation during acceleration
- Poor fuel economy
03. Step-by-Step Diagnosis
Scan for codes and verify P1370 is present; check for related misfire codes.
Visually inspect ignition coil, spark plugs, and wiring for damage, corrosion, or loose connections.
Test ignition coil primary and secondary resistance with a multimeter and compare to specifications.
Check spark plug condition and gap; replace if worn or incorrect.
If wiring and components appear good, test ICM and PCM operation per manufacturer procedures.
1. Frequently Asked Questions
Is it safe to drive?▼
You can drive short distances, but continued driving may cause misfires, reduced performance, and potential damage to the catalytic converter. It's best to diagnose and repair promptly.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on the root cause. A single ignition coil replacement is around $100-$200, while PCM replacement can exceed $500.