Toyota Prius won’t start – causes and how to fix it

Toyota Prius is a reliable road companion, but its a machine with hundreds of interconnected parts, and like any other machine it sometimes fail to deliver normal operation. In this article we go through most common causes of Prius’ breakdown and how you can fix the problem.

The most common causes that hinders normal starting operation of your Prius are dead key fob battery, dead high voltage battery, dead 12v battery. However clogged fuel filter, blown fuse, empty gas tank, immobilizer error or any fault in the electrical system can also cause your vehicle not to start.

1. Dead high voltage battery

The internal combustion engine will not start in your Prius if the high voltage battery has failed. Due to risk of electrocution, as the battery produces over 200 volts, its recommended to get it checked by a professional mechanic.

2. Dead 12v battery

Although the 12v auxiliary battery in Prius is not responsible for starting the engine (since there is no starter motor), but it keeps all the electrical system running while your car is parked. The voltage of the battery on your Toyota Prius can be measured precisely with a multimeter. Before the test, the multimeter is set to the voltage range of the battery and connected to its plus and minus poles. Successful testing of the car battery, i.e. checking the voltage, usually results in values ​​of approx. 12 to 13 volts.

Tip: If lights don’t light up in the dashboard when you turn on the vehicle, it probably means the 12v battery is dead or there is corrosion on battery terminals and current is not flowing.

3. Weak key fob battery

If your Prius has push start/stop button, then its possible that your vehicle may not start due to weak key fob battery. Don’t worry, you can still start your vehicle – the battery is only used to send the signal for locking/unlocking. If the key fob battery is empty, the door no longer locks or unlocks at the push of a button. The doors must then be opened manually. The immobilizer is controlled by a passive transponder. Passive means, among other things, that the transponder in the key does not need its own power source.

How to start Toyota Prius with dead key fob battery

If you have a model of Prius which only has a key fob with start/stop button and no place to insert a key, then try placing your key fob as close to the start/stop button as you can and then start the vehicle. If it doesn’t work, then look in your vehicle’s operational manual for exact location of key fob placement, as it may vary depending on model.

Tip: You can try starting your Prius with its second key. It will also rule out any other problem with the first key, for example, water damage.

4. Clogged fuel filter

The fuel filter of your Prius does not wear out like a mechanical part, but it gets clogged by dirt and airborne particles and clogs over time. The permeability of the filter drops, and so does the fuel pressure. To a certain extent this doesn’t matter, but if the fuel filter is too dirty, the engine will no longer perform at full capacity and in some instance may not start at all. Cleaning is not possible, you can only change the filter.

5. Fuel pump failure

If your Prius’ fuel pump fails, then the engine won’t start. The pump normally ensures that the necessary amount of fuel is passed from the tank to the injection system of the engine with sufficient pressure.

Before your fuel pump stops working, it usually becomes noticeable: if your car’s engine breaks down from time to time, the car is difficult to start, the engine jerks a little or the engine performance drops, you should have your pump checked.

Wear or contamination of the pump can be the reason for this. If the pump is leaking, a power contact is broken, a line or a pump lever is broken, the fuel pump is usually also noticeable before failure. You can have a defective fuel pump replaced in your workshop.

6. Blown fuse

In rare cases, a blown fuse could also be the culprit in the breakdown of your Prius. Check all fuses in the fuse box essential for starting the engine. But, be careful when lending a hand yourself to the fuse box! The box is under power and repairs or tests should always be done in a workshop.

7. Defective spark plugs

Without functioning spark plugs, the engine will not start. The spark plugs themselves are often not affected by a defect. Instead, plug connections on the ignition system come loose. If only one plug is actually loose, you can fix the problem yourself on site. If a spark plug has failed, it must be replaced in the workshop.

8. Rodent damage

Rodent damage can be another reason why your Toyota Prius won’t start. The animals crawl under the vehicle and bite through cables and wires. In principle, this can affect all vehicle systems such as the fuel supply, the oil supply or the power supply.

The rodent damage can usually be seen quickly by looking into the engine compartment. The damage caused by the rodent bite can be repaired in the workshop. Be prepared for relatively high costs here.

9. Engine failure

Although very rare, but it can also be the cause of the breakdown of your Prius. If a vehicle has an engine failure, then nothing works anymore. It is not uncommon for the driver of a vehicle to be responsible for such damage. Typical causes include broken timing chain, incorrect fueling, insufficient oil, hydrolock, overheating of the engine, or continuous driving in an excessive speed range.

Only an experienced mechanic can diagnose engine failure in a workshop.

Use OBD2 scanner for diagnosis

Since Toyota Prius is equipped with on-board diagnostics (OBD), a fault diagnosis can provide initial indications of where the malfunction is located.

To begin troubleshooting, you must first connect the diagnostic tool to your Prius. The OBDII connector is usually located under the dashboard. With the wire connected, you should turn the ignition on. But be careful not to start the engine. Most diagnostic devices then ask for some information about the vehicle. It is important that you enter this 100% correctly, otherwise the result of the search may be falsified. In addition to the vehicle manufacturer and model, you usually also have to type in the engine and vehicle ID number. For exact troubleshooting, always check whether the information is correct.

Conclusion

There are many reasons why your Prius may not start. When looking for the trigger, it is advisable to use the exclusion principle and only start with the most obvious cause, the empty battery.

In any case, it is advisable for laypersons to call a breakdown service or a workshop. In the event of a defect, the latter can directly initiate the repair.