Parts for your 2021 Toyota Prius-Knock sensor

2021 Toyota Prius knock sensor: what it does and how to look after it

Yes, the 2021 Toyota Prius is fitted with a knock sensor. This is confirmed in Toyota’s technical literature: the Toyota Repair Manual (TIS) for the 2ZR-FXE engine includes “Knock Sensor” inspection and removal/installation procedures and the DTC chart lists P0325 (Knock Sensor “A” Circuit) for this model. Toyota’s New Car Features (NCF) documentation also describes knock control using a piezoelectric sensor mounted to the cylinder block, and the Toyota Electronic Parts Catalogue (EPC) lists a dedicated knock sensor for the 2ZR‑FXE.

On this hybrid, the knock sensor is a small, very sensitive microphone bolted to the engine block. Its whole job is to listen for abnormal combustion—known as knock or pinging—and tell the ECU to tweak ignition timing so the engine stays smooth, efficient and protected. Even though the 2ZR‑FXE runs an Atkinson cycle and typically sips regular 91 RON unleaded, it still benefits massively from real‑time knock feedback, especially under load, on hot days, or with varying fuel quality.

For servicing, the knock sensor isn’t a routine replacement item. It’s a fit‑and‑forget part that should last the life of the vehicle. That said, if the check engine light pops up with codes like P0325, or there are symptoms such as rattly pinging sounds, reduced power, rough running or worse fuel economy, it’s time to investigate.

• Diagnosis: Scan for fault codes (P0325 etc.), check freeze‑frame data, and inspect the sensor harness and connector for corrosion, oil contamination, or damage.
• Replacement: If required, the sensor is mounted on the block under the intake side. Access is tight, so plan for intake component removal. Always torque the sensor to the spec in the Toyota Repair Manual—over‑ or under‑tightening can throw off readings.
• Precautions: Park safely, switch IG OFF, and disconnect the 12‑volt negative terminal so the hybrid system can’t start the engine while hands are under the bonnet.
• Prevention: Use quality fuel, keep the cooling system healthy, fix intake leaks promptly, and ensure engine mounts aren’t flogged out, excess vibration can confuse the sensor.

When done right, a healthy knock sensor helps the Prius run at its best—quiet, frugal and reliable across Aussie and Kiwi conditions.

Where is the knock sensor on a 2021 Toyota Prius?

It’s bolted to the side of the 2ZR‑FXE engine block, beneath the intake manifold area. Access generally requires removing some intake plumbing and associated brackets to reach the sensor and its single electrical connector.

What are the signs a Prius knock sensor is failing?

Common clues include a check engine light with code P0325, reduced performance, harsher engine note or light pinging under load, and a noticeable dip in fuel economy. Wiring damage or a loose sensor bolt can cause similar symptoms, so don’t skip the visual checks.

Do I need to replace the knock sensor as part of regular servicing?

No. It’s not a scheduled service item. Replace it only if diagnostics point to a fault. During routine servicing, a quick look for oil contamination around the connector and verifying no related fault codes is usually plenty.