P1640 Control module faulty

P1640 Control module faulty

A P1640 diagnostic trouble code (DTC) indicates a general fault within a vehicle's control module, with the specific meaning and associated systems varying significantly depending on the make and model

. This code is not universal and can be triggered by issues ranging from an internal module malfunction to problems in related electrical systems. 

Common P1640 definitions by manufacturer

• Volkswagen/Audi: On many 2003–2009 models, P1640 points to an "Internal Control Module: EEPROM Error" in the Bosch EDC16U1 Engine Control Unit (ECU). An issue with the ECU's internal memory can cause various engine performance problems.
• General Motors (GM): For older GM vehicles, this code can indicate a fault with a "Quad Driver Module" (QDM) within the Powertrain Control Module (PCM). A QDM is a chip that controls specific outputs, such as the EVAP purge solenoid or the torque converter clutch solenoid. The code may be caused by a faulty solenoid rather than the PCM itself.
• Mazda: On some models, P1640 may be a reference code indicating that a powertrain-related DTC is stored in another control module, such as the Diesel Exhaust Fluid (DEF) or dosing control unit.
• Hyundai: A P1640 code can refer to a malfunction in the main relay control circuit.
• Porsche (Boxster 986): In these models, P1640 can point to an Engine Control Module (ECM) fault that prevents the engine from cranking or starting. 

Common symptoms

Beyond a lit Check Engine Light, the symptoms of a P1640 code will depend on the specific system affected. 

• Engine performance issues, such as rough idling, stalling, and hesitation.
• Loss of power or the vehicle entering "limp mode".
• No-start or no-crank conditions.
• Erratic transmission shifting.
• Unusual noises, such as a ticking sound from a faulty solenoid. 

Possible causes

• Internal Control Module Fault: This is the most serious potential cause and can include software or EEPROM errors within the Engine Control Module (ECM) or Powertrain Control Module (PCM).
• Faulty Output Driver: The P1640 code may be triggered by a fault in a component controlled by the module, such as the EVAP purge solenoid or torque converter clutch solenoid. A malfunction in the controlled component can lead the PCM to incorrectly report a QDM or module fault.
• Wiring Issues: Damaged, corroded, or shorted wiring harnesses and connectors can interrupt communication and power supply to the control module.
• Poor Electrical Connections: A faulty ECM relay or loose connections can prevent the module from receiving proper power.
• Incorrect Module Coding: After replacing a control module, the P1640 code may set if the new unit is not properly programmed or coded for the vehicle. 

Diagnostic and repair steps

1. Check for other codes: Since P1640 can be a reference code, use a professional-grade scan tool to check for additional DTCs in all control modules. Address any other codes first, as they may be the root cause.
2. Inspect wiring and connections: Perform a visual inspection of all wiring and connectors related to the control module. Look for signs of damage, corrosion, or loose connections.
3. Test related components: If the code points to an output driver (QDM) fault, test the specific components it controls, such as the EVAP solenoid or transmission solenoids, for proper operation and voltage signals.
4. Perform software updates: For certain manufacturer-specific issues, such as the VW/Audi EEPROM error, check for any available software updates or reprogramming for the ECM.
5. Address the module: If all other possibilities are eliminated, the fault may be internal to the control module.
   • Remanufacture: Some shops specialize in remanufacturing a faulty module, which can be a cost-effective solution for specific issues like the VW/Audi EEPROM error.
   • Replace and Program: In many cases, the control module will need to be replaced. Be aware that the new module will require programming to match your vehicle's features.