Jump-Start a Dead 12V Battery

The Yaris Hybrid keeps its 12 V battery in the boot, so you do not jump it directly. Toyota fits a dedicated +B boost terminal in the engine-bay relay box (under a red flip-up cover) for exactly this job. Here is how to boost a flat 12 V safely and bring the car to READY.

Jump-start the Yaris Hybrid

1. Park the donor car close, both cars switched fully off. Use an ordinary 12 V petrol/diesel car or a booster pack as the source.
2. Open the bonnet and find the fuse/relay box on the right of the engine bay. Unclip and lift off its lid.
3. Flip up the red cover marked + to expose the +B boost terminal.
4. Connect the red jumper lead: one clamp to the Yaris +B terminal, the other to the donor battery positive (+).
5. Connect the black jumper lead: first to the donor battery negative (−), then the other clamp to a solid, unpainted metal bracket or bolt in the Yaris engine bay — not to the 12 V battery in the boot.
6. Run the donor car for three to five minutes to put some charge across.
7. In the Yaris, hold the brake and press the POWER button. A hybrid does not crank — the green READY light means the system is live.
8. With the car in READY, remove the leads in reverse order (black from the Yaris ground, black from the donor, red from the donor, red from the +B terminal), then close the red cover and refit the box lid.
9. Drive, or leave the car in READY for about 30 minutes, to recharge the 12 V battery. If it goes flat again, the battery or a parasitic drain needs checking.

Never clamp a lead to the orange high-voltage cables or the hybrid traction battery. The +B terminal only feeds the 12 V system, which is all you need to wake the car.

Frequently asked questions

Where is the 12 V battery on the Yaris Hybrid?

In the luggage compartment, on the right behind the trim. It is a small lead-acid auxiliary battery, completely separate from the high-voltage traction battery under the floor.

Can I jump-start another car from my Yaris Hybrid?

Toyota advises against it. The hybrid has no conventional alternator to sustain a heavy draw, and the 12 V battery is small, so you risk flattening your own car.

The Yaris still will not go to READY after boosting — now what?

Hold the boost for a few more minutes and try again. If the dashboard is still dead, the 12 V battery may be beyond a jump, or a main fuse has blown.

If a warning light or fault code stays on after the battery goes flat, you can look it up on autodtcs.com.