Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
The car's computer is having trouble controlling the engine's idle speed on one side of the engine.
The engine control module (ECM) cannot adjust the idle speed control valve properly for Bank 2, which affects how the engine idles.
The P159C code indicates that the ECM has detected a problem with the adaptation of the idle speed control valve on Bank 2. This means the ECM is unable to correctly adjust the valve to maintain the desired idle speed, possibly due to a mechanical or electrical issue.
• Rough or unstable idle
• Engine stalling at idle
• Check Engine Light illuminated
• Faulty idle speed control valve
• Wiring issues or poor electrical connections
• Carbon buildup in the throttle body
ECM: Engine Control Module
Throttle Body: A component that controls the amount of air entering the engine
• Check for any additional codes and address them first.
• Inspect the wiring and connectors to the idle speed control valve.
• Test the idle speed control valve for proper operation.
• Clean the throttle body to remove carbon buildup.
• Repair or replace damaged wiring or connectors.
• Replace the idle speed control valve if faulty.
• OBD-II scanner
• Multimeter
• Throttle body cleaner
$150 - $400
Moderate
• BMW 5 Series
• Mercedes-Benz E-Class
• Audi A6
• Regular maintenance and cleaning of the throttle body
• Ensure electrical connections are secure
• Use quality fuel to reduce carbon buildup
Engine Performance
• Have the vehicle diagnosed by a professional if unsure.
• Avoid driving the vehicle if the idle is unstable, as it may stall.
Check with the vehicle manufacturer for any applicable warranty on engine components.
This code is often associated with vehicles that have higher mileage or poor maintenance history.
Moderate – Addressing the issue promptly can prevent further engine performance problems.
Operating a vehicle with an unstable idle can be unsafe, especially in traffic conditions.
• Engine at normal operating temperature
• Vehicle in park or neutral
The idle speed control valve is typically located on or near the throttle body of the engine.
Q: Can I drive with a P159C code?
A: It's best to have it checked as soon as possible. Driving with an unstable idle can be unsafe.
Q: What happens if I ignore the P159C code?
A: Ignoring the code may lead to worsening idle issues and potential engine stalling.
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