Ignition Coil Secondary Circuit Failure
The ignition coil's secondary winding (the high-voltage side that creates spark) is failing or has an open circuit, like a broken wire inside the coil preventing electricity from reaching the spark plug. The engine can't fire one or more cylinders properly without this spark.
The ECU monitors secondary coil resistance and spark generation through feedback circuits. It detects abnormal voltage levels, excessive current draw, or absence of spark confirmation signals during ignition events. When resistance exceeds threshold or spark feedback fails, the fault is logged.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Secondary Coil Resistance | 6-15 kΩ typical | >20 kΩ or open circuit (infinite resistance) |
| Spark Confirmation Voltage | 5-12V feedback signal | Below 2V or no signal detected |
Code P1370 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1370 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.