Fault code P1603 – a step-by-step guide to diagnosing and fixing it

Error code P1603 is displayed and the check engine light is on - what does this mean?

The DTC P1603 is a manufacturer-specific fault code that is recognized by the OBD system and indicates a problem with the engine control unit (ECU) or its communication. This trouble code occurs when the EOBD diagnosis detects a fault in the internal processing or storage of data in the engine control unit.

What can cause this error code?

• Defective engine control unit (ECU)
• Corrupt software or firmware in the control unit
• Voltage fluctuations in the power supply
• Damaged wiring to the control unit
• Loose or corroded plug connections
• Electromagnetic interference
• Defective battery or alternator
• Water damage to the control unit
• Overheating of the ECU
• Faulty ground connections

What symptoms occur in parallel with error code P1603?

• Starting problems: The vehicle is difficult or impossible to start
• Irregular idling: Engine runs unevenly or stutters at idle speed
• Loss of power: Reduced engine power while driving
• Jerking: Vehicle jerks when accelerating or idling
• Check engine light: Permanent illumination of the check engine light
• Communication error: OBD scanner cannot establish a connection to the ECU
• Sporadic failures: Intermittent problems with various engine systems

How to fix the problem of fault code P1603?

• Repairing this fault code requires a systematic approach to identify the root cause.
• Perform an ECU reset: Disconnect the battery for 15 minutes and reset the ECU, then delete the fault code and carry out a test drive
• Check the power supply: Measure battery voltage (should be 12.4-12.8V), test alternator and replace defective components if necessary
• Inspect wiring: Check all cables to the ECU for damage, corrosion or loose connections and repair
• Software update: Have the latest firmware for the engine control unit installed by the authorized dealer
• Replace control unit: If the ECU is irreparably damaged, have the entire engine control unit replaced and programmed
• Clean earth connections: Clean and tighten all ground connections of the ECU and treat with contact spray