Fault code P1605 – a step-by-step guide to diagnosing and fixing it

Error code P1605 is displayed and the check engine light is on - what does this mean?

The DTC P1605 is a manufacturer-specific fault code that is recognized by the OBD system and indicates a problem with the engine control unit (PCM/ECM). This trouble code occurs when the EOBD system detects a fault in the internal communication or processing of the control unit. Depending on the vehicle manufacturer, the exact definition of fault code P1605 may vary, but typically refers to internal PCM errors or memory problems.

What can cause this fault code?

• Defective engine control unit (PCM/ECM)
• Corrupt software or firmware in the control unit
• Voltage problems in the power supply of the PCM
• Damaged internal memory modules
• Overheating of the engine control unit
• Electromagnetic interference
• Faulty ground connections to the control unit
• Defective internal processors or circuits

What symptoms occur in parallel with fault code P1605?

• Starting problems: The vehicle is difficult or impossible to start
• Engine misfires: Irregular engine running and jerky driving
• Loss of power: Reduced engine power and poor acceleration
• Emergency running program: Engine only runs in emergency mode with limited power
• Electronic problems: Failure of various control unit functions
• Irregular idling: Engine runs unevenly at idle speed
• Complete engine failure: In severe cases, the engine no longer starts

How to fix the problem of error code P1605?

• Repairing the P1605 usually requires professional diagnosis, as the problem is internal to the control unit.
• Carry out a control unit reset: Disconnect battery for 30 minutes and allow all capacitors to discharge, then reinitialize control unit
• Install software update: Have the latest firmware for the PCM installed by the authorized dealer
• Check the power supply: Check all fuses, relays and cable connections to the engine control unit and replace defective parts
• Clean earth connections: Clean and tighten all ground points on the control unit
• Replace the engine control unit: In the event of irreparable internal damage, replace the entire PCM with an original spare part and have it programmed
• Professional diagnosis: Visit a specialized workshop with manufacturer-specific diagnostic equipment