Car Won’t Start Hybrid Interlock Circuit Open
Hybrid vehicles from Toyota, Honda, Ford, Audi, VW, BMW, and Mercedes-Benz utilize interlock circuits for the hybrid system. If the interlock circuit is tampered with, the vehicle will not start.
A fault code such as “The interlock circuit of the high-voltage on-board electrical system has a malfunction.” will get triggered and disable the engine start.
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The high-voltage system on hybrid vehicles can utilize up to 360 volts. Such voltage can cause injuries or even death when an untrained technician works on the hybrid system.
The YOUCANIC scanner can be used to check the status of the interlock circuit or read codes from the hybrid battery (BMS). The hybrid vehicle interlock circuit is designed to disable engine start for safety reasons. One of the main functions is preventing injuries to anyone not trained to work with the high-voltage system.
The following problems can cause the interlock circuit to be open and prevent the engine from starting:
- The interlock safety connector has been removed.
- High voltage (orange) cables are damaged.
- The high voltage loop is broken.
Interlock Safety Connector
Typically, the high voltage safety connector, or the interlock safety connector, is mounted on the power electronic module. An interlock safety connector may also be mounted near the 12-volt or high-voltage battery on some makes. The connector will de-energize the high-voltage system if it is accidentally disconnected or if anyone tampers with it.
When the high-voltage safety connector is removed, the interlock circuit is broken, and the high-voltage system is automatically turned off. In most cases, you will not be able to start the vehicle.
A fault code related to a high-voltage interlock loop will be stored in the ECU or hybrid system control module. The vehicle may not start even after connecting the safety connector. Fault codes will often need to be cleared to start the engine. The high-voltage safety connector should only be removed when the ignition is off.
Damaged Cables
The cables for the high-voltage system can get damaged, especially if the vehicle has been in an accident. In addition, the high-voltage cables may have an inline fuse that may blow. If the fuse is blown, the high-voltage system gets switched off. When reconnecting the orange hybrid cables, ensure they are fully connected and secured.
If the high voltage cables are damaged, it is recommended to replace them instead of repairing the damaged cable.
If the high-voltage cables are disconnected, you will also see a hybrid battery warning symbol on the instrument cluster.
The high voltage loop typically runs the high voltage battery to the electrical A/C compressor rather than the electric machine. The electric machine sits between the engine and the transmission. The electric machine power electronic unit (also called electrical machine electronics) is mounted to the side or top of the transmission.
Fault codes such as the interlock circuit of the high-voltage onboard electrical system a malfunction that may stay present even after the interlock safety connector has been connected. To start the vehicle, you will need a professional diagnostic scanner to reset such fault codes.
Get Help
If you are having issues with the hybrid, please “contact the YOUCANIC” team with any questions that you may have.
We can help you troubleshoot the problem FREE of charge if you send us the codes. We need the fault codes from these four modules:
- Engine ECU,
- DC/DC converter,
- BMS – Battery Management System
- SG-ME Power Electronics Module
Once we have the codes, we can tell you if you have a bad power electronic module, hybrid battery, or both.
If your vehicle is at the dealership or mechanic, ask them for the list of codes and send them to us. If you want to ship the car to Baltimore, we can repair it at a fraction of the dealer’s cost. We love these cars and believe it is a sin to pay over $10k to keep them running.
We hope you find the Car Won’t Start Hybrid Interlock Circuit Open guide helpful. Check these troubleshooting and repair guides for more help on your vehicle.
