What does it mean?
P1558 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle Actuator Electrical Malfunction .
Symptoms
- Check engine light on and the reduced power or throttle warning lamp illuminated
- Engine drops into limp mode with the throttle held at a fixed low opening
- Idle speed too high, too low, or hunting up and down
- Accelerator pedal feels dead, or the engine responds with a long delay
- Engine stalls when coming to a stop or when the air conditioning cuts in
- Vehicle cannot exceed a low road speed even with the pedal fully pressed
Likely causes
- Heavy carbon build-up on the throttle plate and bore, which forces the motor to draw excessive current
- Worn brushes or an open winding in the throttle actuator motor
- Corroded, wet or loose throttle body connector
- Chafed or broken wiring between the PCM and the throttle actuator
- Weak battery or poor charging, since low supply voltage upsets the throttle control loop
- Throttle body cleaned or replaced without carrying out the required adaptation procedure
- Failed throttle driver stage inside the PCM
How to fix it
- Check battery condition and charging voltage first, because low voltage alone can set this fault
- Inspect and reseat the throttle body connector, looking for water, corrosion and spread terminals
- Compare the requested and actual throttle position values on the scan tool with the engine running
- Clean carbon from the throttle bore and plate using the manufacturer approved method, never forcing the plate by hand
- Measure the actuator motor resistance and check the control wires for continuity and shorts
- Perform the throttle adaptation or relearn procedure after any cleaning, disconnection or replacement
- Replace the throttle body when the motor is proven faulty, then repeat the adaptation and road test