Fault code P1503 – a step-by-step guide to diagnosing and fixing it

Error code P1503 is displayed and the check engine light is on - what does this mean?

The DTC P1503 is a manufacturer-specific trouble code that is recognized by various OBD and EOBD systems and typically indicates problems with the idle speed control or the throttle valve system. This fault code can have different meanings depending on the vehicle manufacturer, but usually relates to the electronic engine control unit and the engine's air supply.

What causes can this fault code have?

• Defective throttle valve or throttle valve actuator
• Dirty or defective idle speed actuator (IAC valve)
• Damaged or blocked intake manifold
• Faulty wiring to the throttle valve sensor
• Defective mass air flow sensor or MAP sensor
• Loose or corroded plug connections
• Vacuum leak in the intake system
• Defective engine control unit (ECU)
• Dirty air filter
• Problems with the fuel supply

What symptoms occur in parallel with fault code P1503?

• Irregular idling: The engine runs erratically or fluctuates in speed when idling
• Starting problems: The vehicle is difficult to start or does not start immediately
• Stalling of the engine: The engine stalls, especially when idling or when stopping
• Increased fuel consumption: Noticeably higher consumption due to inefficient combustion
• Jerking when accelerating: Uneven power delivery when accelerating
• Reduced engine power: Noticeable loss of power, especially at low engine speeds

How can the problem with error code P1503 be rectified?

• Repairing error code P1503 requires a systematic diagnosis and various solutions depending on the cause.
• Clean or replace the throttle valve: Remove the throttle valve, clean it thoroughly with special cleaner and check the function of the actuator motor
• Replace the idle speed actuator (IAC valve): Locate the IAC valve, disconnect the electrical connections and replace the defective component
• Check and clean the mass air flow sensor: Remove the MAF sensor, clean it with special MAF cleaner or replace it if defective
• Check the intake system for leaks: Use spray or smoke test to find vacuum leaks and seal any leaks
• Check wiring and plug connections: Check all cable connections for damage, corrosion or loose contacts and repair them
• Replace air filter: Replace a dirty air filter with a new one to ensure optimum air supply