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Hybrid cars are pleasurable to drive but this experience can turn sour when the car suddenly leave you stranded on the road. Every car has its issues and so does hybrids. Compared to conventional cars, hybrids also do have many pros.  
One of the commonly reported faults of hybrid cars is they shutting off while on motion. Unfortunately, the diagnosis of this kind of issue often require deep knowledge of the hybrid system. This is why we are putting this article up to make it easy for anyone to get to the root cause of the fault.


What can cause a hybrid car to go off while on motion?

We will concentrate on faults that are peculiar to hybrid cars and not those that are general to all cars like bad fuel pump.  

1. Weak hybrid battery 

The hybrid battery also known as traction or high voltage battery when weak can cause the car to shut off on motion. There are symptoms that accompany a dying hybrid battery and they should be paid attention to.  

What causes the hybrid battery to become weak?  

(a). Aging 

This is due to normal depreciation of the battery due to use and age.  

(b). Faulty cell 

A cell or more that is bad in the battery pack can cause the pack to become weak. There are various causes that affects cells in the hybrid battery pack.  

(c). High battery temperature 

A cooling fan is installed in the battery pack to cool it. If there is an issue with this cooling system, the battery overheats and over time becomes weak. Sometimes, the fan itself still works but other things cause the battery to overheat and make the fan noisy.  

(d). Leaving hybrid car's transmission on neutral  

Leaving the transmission of a hybrid car on neutral while in traffic or when stationary is a bad practice as the battery charge drains without being replenished.

Sometimes, it is easy to spot hybrid battery that is becoming weak as the fuel efficiency reduces due to various reasons.


2. A faulty hybrid car inverter 

A bad inveter/converter system can cause a hybrid car to shut off while it is being driven.


3. A fault in the transaxle of the hybrid car 

The transaxle houses the split power device and the motor/generator sets. The motor/generator sets are responsible for charging the high voltage battery through either regenerative braking or by converting the internal combustion engine's mechanical power to electrical power. When there is a problem with this system, the traction battery won't charge effectively or won't charge at all.  
One common mistake by owners is the use of wrong transmission fluid in the eCVT which has adverse effect on the transmission. 

Below are the common causes of a hybrid's transaxle fault  

(a). A mechanical fault in the transaxle  

(b). A electrical fault especially that of the motor/generator sets.  

(c). A wrong fluid in the transaxle.  

Putting a fluid of wrong specification is one of the common causes of battery not charging efficiently and car shutting off. This issue is also difficult to diagnose by an average technician.

Other causes of hybrid car shutting off while being driven include but not limited to:  
1. Faulty ICU (internal combustion unit).  
2. Bad fuel pump.  
3. Bad sensors.  
4. Electrical/wiring faults.