Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that there is a problem with the ignition coil in cylinder number 8 of your car. The ignition coil is like a spark plug's helper, and if it doesn't work right, the car might not run smoothly.
The P138C code indicates an issue with the ion sensing circuit in the ignition coil for cylinder 8. This can lead to misfires or poor engine performance.
The ignition coil is responsible for converting the battery's voltage to a higher voltage needed to create an electric spark in the spark plugs. The ion sensing circuit monitors the combustion process and helps in detecting misfires. A fault in this circuit can lead to improper combustion in cylinder 8.
• Engine misfire
• Rough idle
• Check Engine Light on
• Faulty ignition coil for cylinder 8
• Wiring issues in the ignition coil circuit
• Faulty spark plug in cylinder 8
Ignition Coil: A component that converts the battery's voltage to a higher voltage needed for spark plugs.
Misfire: A failure of the air/fuel mixture in the engine cylinder to ignite properly.
• Use an OBD-II scanner to confirm the code.
• Inspect the ignition coil and wiring for cylinder 8.
• Test the spark plug in cylinder 8.
• Replace the ignition coil for cylinder 8.
• Repair or replace damaged wiring.
• Replace the spark plug in cylinder 8.
• OBD-II scanner
• Multimeter
• Socket set
$100 - $300
Moderate
• Ford F-150
• Chevrolet Silverado
• Dodge Ram
• Regularly inspect ignition components.
• Replace spark plugs at recommended intervals.
• Ensure proper maintenance of vehicle electrical systems.
Engine Performance
• Avoid driving the vehicle if misfiring occurs.
• Schedule a repair with a professional mechanic.
• Regularly check for updates on vehicle recalls or service bulletins.
Check with your vehicle manufacturer for warranty coverage on ignition components.
The P138C code has been associated with vehicles using ion sensing ignition systems, which are designed to improve combustion monitoring.
Moderate – While the vehicle may still be drivable, ignoring the issue can lead to further engine damage.
Driving with a misfiring engine can lead to increased emissions and may not comply with local emission regulations.
• Engine at operating temperature
• Vehicle stationary
The ignition coil for cylinder 8 is typically located on the engine block, near the rear of the vehicle on V8 engines.
Q: Can I drive with a P138C code?
A: It's not recommended to drive with this code as it can lead to further engine damage.
Q: How can I prevent ignition coil issues?
A: Regular maintenance and timely replacement of spark plugs can help prevent ignition coil issues.
High-End · Full-system diagnostics
A full-system bidirectional platform aimed at advanced DIY users and professional diagnostic workflows.
Network faults often require full-system access instead of a generic code reader alone.
View on Amazon
Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
View on Amazon
Universal · Wire connectors and repair kit
Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
View on AmazonThese are optional diagnostic tools, not guaranteed fixes. As an Amazon Associate I earn from qualifying purchases.
Fitment Required · Vehicle-fitment part
Commonly relevant for misfire, ignition-efficiency, and some drivability-related repairs.
Misfire and ignition-related faults commonly involve spark plugs as part of the repair path.
Check the correct plug type, gap, and engine application for your vehicle.
View options on Amazon
Fitment Required · Vehicle-fitment part
Relevant when the fault points toward ignition-coil performance or cylinder-specific ignition issues.
Some ignition faults involve coil performance or cylinder-specific coil problems.
Match the coil to your engine and confirm the failed component before ordering.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.