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 car's computer is having trouble getting a good signal from the engine's spark plugs on one side of the engine. It's like trying to listen to a radio station that's not coming in clearly.
The P1387 code indicates that the ionic current signal from the spark plugs on Bank 1 is lower than expected. This signal is used to monitor combustion quality.
The ionic current signal is generated by the spark plugs during combustion. It is used by the engine control module (ECM) to assess the quality of combustion in the cylinders. A low signal can indicate issues with the spark plugs, ignition coils, or wiring.
• Check Engine Light illuminated
• Rough engine idle
• Decreased fuel efficiency
• Faulty spark plugs
• Defective ignition coils
• Wiring issues or poor connections
Ionic Current: A signal generated by the spark plugs used to monitor combustion.
Bank 1: The side of the engine containing cylinder 1.
• Use an OBD-II scanner to verify the code.
• Inspect spark plugs and ignition coils for damage.
• Check wiring and connections for corrosion or damage.
• Replace faulty spark plugs.
• Replace defective ignition coils.
• Repair or replace damaged wiring.
• OBD-II scanner
• Multimeter
• Socket set
$100 - $300
Moderate
• BMW 3 Series
• BMW 5 Series
• BMW X5
• Regularly inspect and replace spark plugs.
• Ensure ignition coils are in good condition.
• Maintain clean and secure electrical connections.
Sensor Issue
• Do not ignore the Check Engine Light.
• Seek professional diagnosis if unsure.
• Regular maintenance can prevent this issue.
Check your vehicle's warranty for coverage on ignition system components.
This code is commonly associated with BMW vehicles due to their advanced ignition systems.
Moderate – It should be addressed soon to avoid further engine performance issues.
Driving with an illuminated Check Engine Light can lead to increased emissions and potential engine damage.
• Engine at operating temperature
• Vehicle in idle or under light load
The spark plugs and ignition coils are located on the engine's cylinder head, Bank 1 refers to the side with cylinder 1.
Q: Can I drive with a P1387 code?
A: It's possible to drive short distances, but it's best to fix the issue soon to avoid further problems.
Q: How do I know if my spark plugs are bad?
A: Look for signs like rough idle, poor acceleration, or increased fuel consumption.
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.