Parts for your 2003 Toyota Highlander-Knock sensor

2003 Toyota Highlander knock sensor — what it does and when to replace it

Based on Toyota’s factory service literature (TIS engine control system documentation and wiring diagrams), the 2003 Highlander is equipped with knock sensing: the 2.4‑litre 2AZ‑FE uses a single knock sensor on the block, while the 3.0‑litre 1MZ‑FE V6 uses knock sensing per bank via the engine control module. Toyota’s Electronic Parts Catalogue for ACU25/MCU25 models also lists knock sensor components for this year, and common OBD‑II diagnostics (P0325/P0330) in Toyota manuals specifically cover this vehicle. So yes—the knock sensor is fitted and relevant on a 2003 Highlander.

On a 2003 Toyota Highlander, the knock sensor is the engine’s “ears”. It picks up the high‑frequency vibration from detonation (pinging) and alerts the ECU, which then trims ignition timing to stop knock. That keeps the motor safe under load, helps maintain smooth performance, and can improve fuel economy by letting timing run as advanced as conditions allow. Whether it’s the 2.4‑litre four or the 3.0‑litre V6, the goal’s the same: protect the engine and keep it feeling tidy on Aussie and Kiwi roads.

It’s not a routine service item like oil or filters, but it is worth a look if the check engine light shows P0325 or P0330, there’s a rattle under load, the car feels flat, or fuel use climbs. On the 2AZ‑FE, the sensor bolts to the block beneath the intake side. On the 1MZ‑FE V6, the knock sensors and sub‑harness sit under the intake in the “V”, so replacement is more labour‑intensive. When going in that far on a V6, many techs replace both sensors and the sub‑harness together to avoid a repeat job.

• Use quality parts (genuine or reputable OEM‑equivalent) and torque the sensor to the workshop spec to ensure proper sensitivity.
• Inspect the connector and wiring for oil/coolant intrusion or brittle insulation—wiring faults are a common cause of knock‑sensor codes.
• If detonation persists on hot days or steep climbs, check cooling system health and consider using the recommended octane for local fuel quality.

If the intake has to come off (especially on the V6), it’s a good time to refresh gaskets, clean the throttle body, and check vacuum hoses. After replacement, clear codes and confirm timing correction and knock counts look normal on a scan tool during a controlled road test.

Popular questions

Where is the knock sensor on a 2003 Highlander?
On the 2.4‑litre 2AZ‑FE it’s mounted on the block below the intake side. On the 3.0‑litre 1MZ‑FE V6 the knock sensors and their sub‑harness live in the valley beneath the intake manifold, which means the upper intake has to come off to reach them.

Is it safe to drive with a P0325 or P0330 code?
The ECU will usually pull timing to protect the engine, so it may run flat and use more fuel. Short trips to a workshop are generally fine, but continued driving under load risks detonation if the system can’t detect or control knock properly. Get it checked sooner rather than later.

Should both knock sensors be replaced on the V6?
Best practice on the 1MZ‑FE is to replace both sensors and the sub‑harness together if one has failed, because access is the same and ageing components can cause repeat faults. It saves labour and reduces the chance of another tear‑down.