Faulty ignition coil or igniter assembly for cylinder number four; Worn or damaged spark plug or spark plug boot; Damaged or corroded wiring or connector at the ignition coil or igniter; Open or short circuit in the ignition control wire between the ECM and the igniter; Failed igniter module internal electronics; ECM internal driver fault (rare but possible)

DTC codes / Toyota codes / P1315

P1315 · ToyotaIgniter Circuit Malfunction No 4

Q: What does code P1315 mean?

Igniter Circuit Malfunction No 4. P1315 on a Toyota means the engine control module (ECM) has detected a fault in the ignition circuit for cylinder number four, specifically the igniter or coil-on-plug assembly that fires that cylinder. The ECM monitors the ignition feedback signal and sets this code when the expected firing confirmation is missing or erratic, indicating the circuit cannot reliably trigger the spark.

P1315 on a Toyota means the engine control module (ECM) has detected a fault in the ignition circuit for cylinder number four, specifically the igniter or coil-on-plug assembly that fires that cylinder. The ECM monitors the ignition feedback signal and sets this code when the expected firing confirmation is missing or erratic, indicating the circuit cannot reliably trigger the spark.

SystemPowertrain

Code typeToyota specific

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Check engine light illuminated, often with no other noticeable symptoms
Rough idle or misfire felt as a shake or stumble, especially at idle or low speed
Loss of power or hesitation during acceleration
Increased fuel consumption due to incomplete combustion
In some cases, the engine may enter limp mode or flash the check engine light if the misfire is severe

Common causes, most likely first

Faulty ignition coil or igniter assembly for cylinder number four
Worn or damaged spark plug or spark plug boot
Damaged or corroded wiring or connector at the ignition coil or igniter
Open or short circuit in the ignition control wire between the ECM and the igniter
Failed igniter module internal electronics
ECM internal driver fault (rare but possible)

How to diagnose and fix it

Inspect the ignition coil and spark plug for cylinder four for physical damage, corrosion, or wear; replace if suspect.
Check the electrical connector at the ignition coil for tightness, corrosion, or pushed-back pins; clean and reseat as needed.
Test the ignition coil primary and secondary resistance with a multimeter and compare to factory specifications; replace if out of range.
Perform a spark test on cylinder four using an inline spark tester to confirm whether spark is present.
Check for continuity and short circuits in the ignition control circuit between the ECM and the igniter, repairing any damaged wires.
Swap the ignition coil from cylinder four with a known-good coil from another cylinder to see if the misfire moves; if it does, replace the coil.
If all external components test good, diagnose the ECM driver circuit for the number four ignition output, which may require professional scan tool actuation tests.

Igniter Circuit Checks Before Coil Replacement

A loose or corroded connector at the ignition coil is a frequent cause of P1315 that many people overlook when they replace the coil itself.
The code can be set by a failing spark plug that increases resistance and stresses the igniter circuit, so always inspect the plug before condemning the coil.
On some Toyota engines, the igniter is integrated into the coil-on-plug assembly, so a coil swap test is the quickest way to confirm the fault.
P1315 is often accompanied by a misfire code for the same cylinder, but the absence of a misfire code does not rule out an intermittent igniter circuit problem.
A weak battery or poor ground connection can cause voltage spikes that damage the igniter, so check the charging system and engine grounds as part of the diagnosis.

Can I keep driving with P1315?

You can drive the vehicle short distances to a repair shop, but avoid heavy acceleration or sustained high-speed driving because a persistent misfire can overheat the catalytic converter and cause costly damage. If the check engine light is flashing, stop driving and have the vehicle towed.

Tools that help

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