Faulty ignition coil on cylinder 4 (internal short or degraded insulation causing early triggering); Worn or contaminated spark plug on cylinder 4, altering ionization feedback; Damaged or chafed wiring harness to the cylinder 4 coil, causing intermittent signal shorts; Corroded or loose electrical connector at the cylinder 4 coil; Engine control module (ECM) software calibration issue or internal driver fault; Poor engine ground or voltage supply fluctuation affecting coil charging; Mechanical issue such as low compression or valve problem on cylinder 4 that mimics an ignition fault

DTC codes / Jaguar codes / P1374

P1374 · JaguarIgnition Coil Cylinder 4 Early Activation Fault

Q: What does code P1374 mean?

Ignition Coil Cylinder 4 Early Activation Fault. P1374 on a Jaguar indicates that the engine control module (ECM) has detected an early activation fault for the ignition coil on cylinder 4, meaning the coil fired before the commanded timing or the feedback signal arrived outside the expected window. The ECM monitors the coil's primary circuit and ionization feedback to flag this as a pending or confirmed fault when the activation event occurs too soon relative to the crankshaft position signal.

P1374 on a Jaguar indicates that the engine control module (ECM) has detected an early activation fault for the ignition coil on cylinder 4, meaning the coil fired before the commanded timing or the feedback signal arrived outside the expected window. The ECM monitors the coil's primary circuit and ionization feedback to flag this as a pending or confirmed fault when the activation event occurs too soon relative to the crankshaft position signal.

SystemPowertrain

Code typeJaguar specific

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Intermittent misfire or rough running, especially under load or during acceleration
Slight hesitation or stumble when the engine is cold or during light throttle
Reduced fuel economy due to incomplete combustion on cylinder 4
In rare cases, a flashing check engine light if the misfire becomes severe enough to risk catalytic converter damage

Common causes, most likely first

Faulty ignition coil on cylinder 4 (internal short or degraded insulation causing early triggering)
Worn or contaminated spark plug on cylinder 4, altering ionization feedback
Damaged or chafed wiring harness to the cylinder 4 coil, causing intermittent signal shorts
Corroded or loose electrical connector at the cylinder 4 coil
Engine control module (ECM) software calibration issue or internal driver fault
Poor engine ground or voltage supply fluctuation affecting coil charging
Mechanical issue such as low compression or valve problem on cylinder 4 that mimics an ignition fault

How to diagnose and fix it

Perform a visual inspection of the cylinder 4 coil, connector, and wiring for damage or corrosion
Swap the cylinder 4 ignition coil with a known-good coil from another cylinder and see if the fault follows the coil
Replace the spark plug on cylinder 4 and check gap and condition
Use a multimeter to check resistance and continuity of the coil primary and secondary circuits, and inspect the harness for shorts to ground or power
Check for technical service bulletins (TSBs) or ECM software updates specific to Jaguar models for this code
If the fault persists after coil and plug replacement, perform a compression test and cylinder leak-down test to rule out mechanical issues
As a last resort, diagnose the ECM driver circuit with an oscilloscope or substitute a known-good ECM for testing

When P1374 is not the coil itself

A swapped coil that does not move the fault suggests the problem lies in the wiring harness or ECM driver, not the coil.
Early activation faults can be triggered by a failing crankshaft position sensor or reluctor ring, causing timing reference errors that the ECM interprets as coil fault.
Jaguar models with coil-on-plug ignition are sensitive to spark plug brand and gap; using incorrect plugs can cause ionization feedback anomalies.
Intermittent faults often appear only during cold start or high load, so a road test with a scan tool recording live data is more reliable than a static check.
Some aftermarket coils have different inductance characteristics that can set P1374 even when they function, so OEM or equivalent quality parts are recommended.

Can I keep driving with P1374?

You can usually continue driving if the check engine light is steady and the engine runs smoothly, but avoid aggressive acceleration or heavy loads until diagnosed. If the light flashes or you feel a noticeable misfire, stop driving to prevent catalytic converter damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Jaguar vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.