What is an OBD2 code?

An OBD2 (On-Board Diagnostics) code is a diagnostic trouble code (DTC) generated by your vehicle's computer system when it detects a problem. These codes help identify specific issues with your vehicle's engine, transmission, emissions, or other systems.

How do I read OBD2 codes?

To read OBD2 codes, you'll need an OBD2 scanner. Plug it into your vehicle's OBD2 port (usually located under the dashboard), turn your key to the 'ON' position, and follow your scanner's instructions to retrieve the codes. Each code starts with a letter (P, B, C, or U) followed by four numbers.

What do the different types of OBD2 codes mean?

OBD2 codes are categorized by their first letter: P (Powertrain) for engine and transmission issues, B (Body) for interior systems like airbags, C (Chassis) for mechanical systems like brakes, and U (Network) for computer and module communication problems.

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Home » OBD2 Codes » P1387

Code P1387

Symptoms

• Check Engine Light illuminated

• Rough engine idle

• Decreased fuel efficiency

Common Causes

• Faulty spark plugs

• Defective ignition coils

• Wiring issues or poor connections

Glossary

Ionic Current: A signal generated by the spark plugs used to monitor combustion.

Bank 1: The side of the engine containing cylinder 1.

Related Codes

• P1388

• P1389

Official description

Ionic Current Signal Low (Bank 1)

Laymans terms

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.

Explanation

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.

Technical description

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.

Diagnosis steps

• 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.

Repair procedures

• Replace faulty spark plugs.

• Replace defective ignition coils.

• Repair or replace damaged wiring.

Tools required

• OBD-II scanner

• Multimeter

• Socket set

Estimated repair cost

$100 - $300

Difficulty level

Moderate

Commonly affected vehicles

• BMW 3 Series

• BMW 5 Series

• BMW X5

Preventive measures

• Regularly inspect and replace spark plugs.

• Ensure ignition coils are in good condition.

• Maintain clean and secure electrical connections.

Error code type

Sensor Issue

User experience recommendations

• Do not ignore the Check Engine Light.

• Seek professional diagnosis if unsure.

• Regular maintenance can prevent this issue.

Warranty information

Check your vehicle's warranty for coverage on ignition system components.

Historical data

This code is commonly associated with BMW vehicles due to their advanced ignition systems.

Urgency level

Moderate – It should be addressed soon to avoid further engine performance issues.

Legal and safety notice

Driving with an illuminated Check Engine Light can lead to increased emissions and potential engine damage.

Testing conditions

• Engine at operating temperature

• Vehicle in idle or under light load

Component location

The spark plugs and ignition coils are located on the engine's cylinder head, Bank 1 refers to the side with cylinder 1.

FAQs

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.

Last updated: Jan 16, 2026 • Source: internal database

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