What Does P1315 Mean?
P1315 indicates a malfunction in the igniter circuit for cylinder number 4. The ECM has detected an abnormal confirmation signal from the No. 4 igniter power transistor, meaning the spark event is not occurring correctly. This results in a dead or intermittent misfire on cylinder 4.
Common Causes
35%
Failed igniter (power transistor) for cylinder 4
30%
Defective ignition coil on cylinder 4
20%
Corroded or damaged wiring between ECM and igniter
10%
Bad ground connection at the igniter module
5%
ECM igniter driver output failure
Diagnostic Steps
1
Inspect the cylinder 4 ignition coil and igniter connector for corrosion, heat damage, or loose terminals.
2
Swap the cylinder 4 ignition coil with another cylinder's coil, clear codes, and test drive to see if the fault follows.
3
Measure cylinder 4 coil primary resistance (typically 0.5-2.0 ohms) and secondary resistance (6-15k ohms).
4
Verify power supply voltage and ground integrity at the igniter module connector.
5
Check the trigger signal from the ECM to the igniter using an oscilloscope for proper pulse width and frequency.
Estimated Repair Cost
$100 - $450
Parts + labor, varies by vehicle and location
P1315 indicates a malfunction in the igniter circuit for cylinder number 4. The ECM has detected an abnormal confirmation signal from the No. 4 igniter power transistor, meaning the spark event is not occurring correctly. This results in a dead or intermittent misfire on cylinder 4.
The most common cause of P1315 (Igniter Circuit Malfunction (No. 4)) is: Failed igniter (power transistor) for cylinder 4
Typical repair costs for P1315 range from $100 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A persistent cylinder 4 misfire causes rough idle, reduced power, and increased emissions. Unburned fuel reaching the catalytic converter can cause overheating. Address promptly to avoid catalyst damage.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1315 to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition System
Difficulty
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