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DTC codes / Jaguar codes / P1373

P1373 · JaguarIgnition Coil Cylinder 3 Early Activation Fault

P1373 on a Jaguar indicates that the engine control module (ECM) has detected an early activation fault for the ignition coil serving cylinder 3, meaning the coil fired before the commanded spark timing or the feedback signal arrived outside the expected window. The ECM monitors the coil's primary circuit and ionization feedback to flag this condition, which typically points to a failing coil, a wiring fault, or a problem with the ignition control signal for that specific cylinder.

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
  • Rough idle or misfire sensation, especially when the engine is cold
  • Hesitation or stumble during acceleration under load
  • Reduced fuel economy due to incomplete combustion in cylinder 3
  • In rare cases, a flashing check engine light if the misfire becomes severe enough to damage the catalytic converter

Common causes, most likely first

  1. Failing ignition coil on cylinder 3, particularly degraded internal insulation or feedback circuitry
  2. Worn or contaminated spark plug on cylinder 3 causing an abnormal ionization signal
  3. Damaged or chafed wiring in the coil harness connector or the coil trigger circuit for cylinder 3
  4. Corroded or loose electrical connector at the cylinder 3 coil, disrupting the feedback signal
  5. Faulty engine control module (ECM) driver for the cylinder 3 coil, though this is less common
  6. Poor engine ground affecting the coil's reference voltage and feedback accuracy

How to diagnose and fix it

  1. Perform a visual inspection of the cylinder 3 ignition coil, connector, and wiring for damage or corrosion
  2. Swap the cylinder 3 ignition coil with a known-good coil from another cylinder and see if the fault follows the coil
  3. Inspect and replace the spark plug on cylinder 3 if it shows wear, fouling, or incorrect gap
  4. Use a multimeter to check the resistance of the coil primary and secondary circuits against Jaguar specifications
  5. Check for continuity and short circuits in the coil trigger and feedback wires between the coil connector and the ECM
  6. Verify engine ground connections and clean any corroded ground points
  7. If all external components test good, diagnose the ECM driver circuit or replace the ECM as a last resort

Cylinder 3 Coil Faults That Fool Technicians

  • A swapped coil that makes the fault move to another cylinder confirms the coil is at fault, but if the code stays on cylinder 3, the problem is almost always in the wiring or the ECM driver.
  • The early activation fault often sets without a drivability complaint because the coil still fires, just outside the expected timing window, so don't dismiss it as a harmless glitch.
  • A spark plug with excessive gap or high resistance can trigger this code by distorting the ionization feedback signal, even when the coil itself is healthy.
  • Corrosion inside the coil boot or connector pins is a frequent hidden cause on older Jaguars, so inspect the boot and pins closely before condemning the coil.
  • This code can be set by a low battery or charging system issue that causes voltage spikes, so always check battery health and ground integrity before replacing parts.

Can I keep driving with P1373?

You can generally drive the car with this code, but avoid hard acceleration and prolonged high-speed driving until it is repaired, because a worsening misfire can overheat and damage the catalytic converter. If the check engine light begins flashing, stop driving and have the vehicle towed to a repair shop.

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.

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