P1600 Voltage supply P1601 Voltage supply P1602 Voltage supply

P1600 Voltage supply P1601 Voltage supply P1602 Voltage supplyThe OBD-II diagnostic trouble codes P1600, P1601, and P1602 all relate to issues with the voltage supply to the vehicle's engine control module (ECM) or powertrain control module (PCM), as well as related communication faults. The exact meaning of each code can vary between different car manufacturers and models. 

Common causes for these codes

The appearance of these codes often indicates a problem with the vehicle's electrical system, which affects the power or communication to the ECM.

• Weak or failing battery: Low battery voltage is a very common cause, as the ECM needs a stable power supply to function correctly.
• Corroded or loose battery connections: Poor connections at the battery terminals can cause intermittent power loss to the ECM, triggering these codes.
• Faulty alternator or charging system: A malfunctioning alternator can fail to charge the battery properly, leading to low system voltage.
• Poor ground connections: Corroded or loose ground wires can cause voltage fluctuations and disrupt the ECM's power supply.
• Wiring harness issues: Damaged or frayed wiring leading to the ECM or transmission control module (TCM) can disrupt power and communication.
• Faulty ECM or related modules: In some cases, an internal malfunction within the ECM itself or related components like the immobilizer can be the source of the problem. 

Common definitions by code

Because the definitions for these codes can vary, it is important to consult your vehicle's specific service manual to get the correct interpretation.

P1600

• ECM Power Supply Malfunction: This is a common definition, indicating that the ECM's backup power source is malfunctioning or that power to the ECM has been lost.
• Hybrid System Fault: On some hybrid vehicles, this code points to a general fault within the hybrid battery system.
• Ignition Switch Fault: In some vehicles, it can relate to a problem with the ignition switch or the circuit that communicates with the ECM. 

P1601

• ECM/TCM Serial Communication Error: This often means there is a communication problem between the engine control module and the transmission control module.
• Voltage Supply Malfunction (Terminal 30): For some manufacturers, it indicates an issue with the constant 12V power supply to the ECU.
• Injector Correction Malfunction: On certain diesel engines, this code is set when there is a fault with the injector compensation or pilot quantity learning values. 

P1602

• Battery Deterioration: In many vehicles, particularly Toyotas and hybrids, this code signals that the vehicle has detected an abnormally low battery voltage.
• Immobilizer/ECM Communication Error: On Ford and other models, this can mean a communication failure between the anti-theft immobilizer system and the ECM.
• Power Supply Voltage Too Low (Terminal 30): For Audi and Volkswagen models, it points to a low voltage supply at a specific ECM terminal. 

Troubleshooting steps

1. Check the battery: Test your battery's voltage and health. Check for corroded or loose terminals and cables.
2. Inspect ground connections: Follow the negative battery cable to the frame or engine block and ensure all ground points are clean and secure.
3. Inspect fuses and relays: Check all fuses and relays related to the ECM and other control modules.
4. Examine the wiring: Look for any visible damage, chafing, or corrosion in the wiring harness connecting to the ECM.
5. Use a scan tool: Some advanced scanners can help you diagnose communication issues between modules more specifically.
6. Seek professional help: If basic checks don't resolve the issue, a professional mechanic can perform more detailed electrical system and ECM diagnosis.