OBD-II / EOBD Diagnostic Trouble Code Database • Code P1640

OBD-II Fault Code P1640: Internal Control Module (ECU) EEPROM Error / Main Power Relay

Q: What does OBD-II fault code P1640 (Internal Control Module (ECU) EEPROM Error / Main Power Relay) mean and what are its symptoms?

OBD-II Fault Code P1640 indicates: Internal Control Module (ECU) EEPROM Error / Main Power Relay. Common symptoms: Illuminated glow plug / Check Engine light, occasional engine cut-out or no-start condition.

Q: What are the most common causes and fix for code P1640?

Most common causes of fault code P1640 ranked by probability: 1. Cold solder joint inside the main ECU power supply relay (e.g., Relay 109 on VAG TDI!) • 2. Voltage drop during cranking due to a weak battery or corroded ground strap • 3. Corrupted EEPROM checksum after improper chiptuning.

⚠️ Common Symptoms & Driving Behavior

Illuminated glow plug / Check Engine light, occasional engine cut-out or no-start condition.

🔧 Most Common Causes & Repair Guide (P1640)

1. Cold solder joint inside the main ECU power supply relay (e.g., Relay 109 on VAG TDI!) • 2. Voltage drop during cranking due to a weak battery or corroded ground strap • 3. Corrupted EEPROM checksum after improper chiptuning.