P1370 — Ignition Coil Secondary Circuit Failure

For Ford vehicles

insufficient RPM increase during spark test

powertrain (engine/transmission)

Is it safe to drive?

Drive with caution Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P1370 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the ignition system for damage, corrosion, chafing or poor contact.
Subsystem check Swap the coil to another cylinder and see if the fault code follows it.
Subsystem check Inspect spark plugs for wear, oil or carbon tracks and check plug gaps.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P1370 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P1370 (parts and labor, USD, independent shop rates): Replace an ignition coil: $150–$380; Replace spark plugs: $90–$250; Repair coil wiring or connector: $80–$250. Overall, fixing P1370 usually costs between $80 and $380. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What is the most common cause of P1370?

The most common causes are: faulty ignition control circuit in the ECM, damaged coil wiring or connector, failed ignition coil or coil pack.

How much does it cost to fix P1370?

Replace an ignition coil — $150–$380; Replace spark plugs — $90–$250; Repair coil wiring or connector — $80–$250. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

How do I diagnose P1370 myself?

Start with a scan: confirm P1370, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ignition coil secondary circuit, and verify the suspect component against live data before buying parts.

Is it safe to drive with P1370?

Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

What are the symptoms of P1370?

Drivers most often notice: increased fuel consumption, loss of power and jerking, Check Engine Light on, misfires under load or at idle.

When your scan tool displays P1370, it tells you the engine control module has detected a problem in the secondary side of the ignition system. The secondary circuit carries the high-voltage charge from the coil to the spark plugs, and the module watches this circuit closely for signs it is not performing within factory specifications. A fault in this circuit means one or more cylinders may not be firing correctly, which cascades into other drivability problems if left untreated.

The ignition coil transforms the battery's low voltage into the thousands of volts needed to jump the spark plug gap. On the secondary side, the coil output travels through a dedicated wire to the plug. When this path is interrupted or shorted—due to physical damage, contamination, or component failure—the control module records P1370 and triggers the Check Engine Light. The code typically requires multiple drive cycles to set, which is why you may see the light come on after several days of normal driving following an initial occurrence.

P1370 falls within the powertrain fault family managed by your vehicle's OBD2 system. When the code sets, the module also captures a freeze frame snapshot containing engine speed, load, coolant temperature, and vehicle speed at the exact moment of failure. This data is invaluable for reproducing the fault condition during diagnosis.

Common Symptoms of P1370

Check Engine Light illuminates on the dashboard
Engine misfires noticeably during acceleration or at idle
Vehicle feels sluggish with a noticeable loss of power
Acceleration becomes jerky or uneven
Fuel economy drops as the engine compensates for missed combustion events
Engine is difficult to start, especially in humid or wet conditions
In severe cases, the engine may run rough or stall entirely

What Causes P1370?

The most frequent culprit behind P1370 is contamination inside the spark plug well. Moisture seeping past the valve cover gasket or oil leaking from thepcv system creates a conductive path that disrupts the high-voltage arc. Beyond contamination, several other failures can trigger the same code.

Oil or moisture present in the spark plug tube wells
Spark plugs that are worn out, fouled with carbon deposits, or incorrectly gapped
Damaged or chafed wiring feeding the ignition coil
Poor electrical connection at the coil harness connector due to corrosion or loose terminals
Complete failure of the ignition coil or coil pack itself
An underlying fault in the engine control module's ignition driver circuit

How to Diagnose P1370

Working through this code methodically prevents unnecessary part replacements. Follow these steps in order.

Connect an OBD2 scanner and verify P1370 is present in the stored codes. Record the freeze frame data before clearing anything—this snapshot reveals engine operating conditions when the fault occurred and guides your inspection toward the right cylinders.
Look for any accompanying trouble codes. Related electrical or sensor codes often point to the root cause rather than the secondary ignition fault itself.
Perform a thorough visual inspection of the ignition wiring harness and coil connectors. Check for damaged insulation, broken wires, corrosion buildup, and verify all connections are fully seated and secure.
Test the suspected coil by swapping it with a known-good unit from another cylinder. If the fault code migrates to the new cylinder, the coil itself has failed.
Remove and examine the spark plugs. Look for oil fouling, carbon tracking, worn center electrodes, or gaps that fall outside manufacturer specifications.
Clear the code and complete a drive cycle that replicates the freeze frame conditions. Monitor whether P1370 returns; if it does, the underlying issue has not been resolved.

Repair Options with Pricing

Addressing the most likely causes first saves both time and money. Here are the common repair paths for P1370 along with typical parts-and-labor costs at independent shops.

Replace a failed ignition coil or coil pack: $150–$380
Replace worn or fouled spark plugs: $90–$250
Repair damaged coil wiring or replace the harness connector: $80–$250

Total Cost to Fix P1370

The actual repair expense hinges entirely on which component triggered the code. In most cases, addressing contamination or wiring issues falls on the lower end of the range, while full coil replacement occupies the higher end. Overall, fixing P1370 typically runs between $80 and $380 depending on the root cause and your vehicle's design. An accurate diagnosis before purchasing parts is the smartest first step—replacing the most expensive component is rarely where you should begin.

Can You Drive with P1370?

Drive with caution and minimize heavy loads while this code is active. Persistent misfires from an unresolved ignition fault send unburned fuel into the exhaust stream, rapidly overheating and destroying the catalytic converter—a repair that costs far more than fixing the original ignition problem. If the Check Engine Light begins flashing rather than staying solid, stop driving immediately and have the vehicle towed to a shop; continuous misfiring under load is causing immediate damage.