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 the computer in your car has detected a problem with the ignition coil in cylinder number 6. The ignition coil is like a mini power station that helps the spark plugs make a spark to start the engine.
The P138A code indicates that the ion sensing module has detected an issue with the ignition coil in cylinder 6, which is responsible for generating the spark necessary for combustion.
The P138A code is triggered when the Engine Control Module (ECM) detects a malfunction in the ion sensing circuit of the ignition coil for cylinder 6. Ion sensing is used to monitor combustion quality and misfires by measuring ion current in the combustion chamber.
• Check Engine Light is on
• Engine misfires
• Poor engine performance
• Faulty ignition coil in cylinder 6
• Damaged or corroded wiring or connectors
• Faulty ion sensing module
Ignition Coil: A component that transforms the battery's voltage to a much higher voltage to create a spark in the spark plugs.
Ion Sensing: A technology used to detect combustion quality and misfires by measuring ion current in the combustion chamber.
• Use an OBD-II scanner to confirm the code.
• Inspect the ignition coil and wiring for damage.
• Test the ion sensing module for proper operation.
• Replace the faulty ignition coil in cylinder 6.
• Repair or replace damaged wiring or connectors.
• Replace the ion sensing module if necessary.
• OBD-II scanner
• Multimeter
• Socket set
$150 - $400
Moderate
• BMW 3 Series
• Mini Cooper
• Volvo S60
• Regularly inspect ignition components.
• Keep engine components clean and dry.
• Perform routine maintenance checks.
Engine Performance
• Have a professional diagnose the issue.
• Avoid driving the vehicle if misfires are severe.
• Regularly maintain your vehicle to prevent future issues.
Check your vehicle's warranty; ignition components may be covered under the powertrain warranty.
This code is more common in vehicles with advanced ignition systems that use ion sensing technology.
Moderate – Address the issue soon to avoid potential engine damage.
Driving with a misfiring engine can cause increased emissions and potential engine damage.
• Engine running
• Vehicle at operating temperature
The ignition coil for cylinder 6 is located on the engine, directly above cylinder 6, which is typically the sixth cylinder from the front of the engine.
Q: Can I drive with a P138A code?
A: It's not recommended to drive with this code for long periods as it can cause engine damage.
Q: How can I prevent this code from appearing again?
A: Regular maintenance and inspections of the ignition system can help prevent this issue.
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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.
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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.
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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.
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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.