Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means there's a problem with the part of the car that helps spark the fuel in cylinder number 7, which is like one of the car's 'lungs'.
The P138B code is triggered when the engine control module (ECM) detects an issue with the ion sensing ignition coil in cylinder 7. This coil is responsible for creating the spark needed for combustion and also senses ionization to help monitor combustion quality.
The ion sensing ignition coil is a component that not only generates the spark necessary for the combustion process but also measures ionization in the combustion chamber to provide feedback to the ECM. A fault in this coil can lead to misfires or poor engine performance, as the ECM cannot accurately monitor or control the combustion process in cylinder 7.
• Engine misfire
• Rough idling
• Reduced fuel efficiency
• Faulty ignition coil in cylinder 7
• Wiring issues or poor connections
• Faulty ECM
ECM: Engine Control Module, the computer that manages engine functions.
Ionization: The process of forming ions, used in this context to monitor combustion.
• Use an OBD-II scanner to confirm the code.
• Inspect the ignition coil and wiring for damage or disconnections.
• Test the ignition coil for proper operation.
• Replace the faulty ignition coil.
• Repair or replace damaged wiring or connectors.
• Reprogram or replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Socket set
$150 - $400
Moderate
• Chevrolet Silverado
• GMC Sierra
• Cadillac Escalade
• Regular maintenance checks
• Timely replacement of ignition components
• Ensuring proper electrical connections
Ignition System Issue
• Have the vehicle inspected by a professional.
• Avoid driving long distances until the issue is resolved.
Check with the vehicle manufacturer for specific warranty coverage on ignition components.
This code has been associated with vehicles using ion sensing technology for ignition coil monitoring, particularly in certain GM models.
Moderate – It should be addressed soon to prevent further engine performance issues.
Driving with a misfire can lead to increased emissions and potential damage to the catalytic converter.
• Engine at operating temperature
• Vehicle in park or neutral
The ignition coil for cylinder 7 is typically located on the engine near the seventh cylinder, often near the rear of a V8 engine.
Q: Can I drive my car with a P138B code?
A: It's not recommended to drive for long periods with this code, as it can lead to further engine damage.
Q: How do I know if my ignition coil is bad?
A: Symptoms include engine misfires, rough idling, and poor fuel economy. An OBD-II scan can confirm the 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.