Parts for your 2004 Toyota Highlander-Knock sensor

2004 Toyota Highlander knock sensor – what it does and how to look after it

Yes, the 2004 Toyota Highlander is fitted with a knock sensor. Toyota’s own technical literature confirms it: the 2004 Highlander/Kluger Engine Control System section of the Toyota Repair Manual (TIS) lists diagnostic trouble codes P0325 and P0330 for knock sensor circuits, along with inspection procedures. The 2004 Toyota Electrical Wiring Diagram shows the knock sensor signal(s) routed to the ECM. Independent guides such as the Haynes Highlander/RX (1999–2006) manual also cover knock sensor testing and replacement on both the 2.4L 2AZ‑FE and the 3.3L 3MZ‑FE. On the four‑cylinder there’s one sensor on the block, on the V6 there are two sensors mounted in the valley beneath the intake manifold.

What does it do? The knock sensor is a piezoelectric “listener” that detects detonation (pinging) in the engine. When it hears knock, it signals the ECU to gently dial back ignition timing until things are smooth again. That protects the engine from damage, keeps power on song, and helps fuel economy and emissions stay in check even with Aussie/NZ summer heat, hills, and the odd tank of average fuel.

It’s not a routine service item, but it’s smart to keep an eye on the conditions that keep it happy. If the Highlander starts feeling flat, uses more fuel, or lights the check engine lamp with codes like P0325 or P0330, the ECU may be stuck in a safe (retarded timing) mode because it can’t trust the knock signal. Before blaming the sensor, rule out basics: correct fuel octane, no intake leaks, tidy earths, healthy cooling system, and no rodent‑nibbled wiring.

When replacement is needed, go for a genuine or OE‑quality (Denso) sensor and don’t cheap out on the little sub‑harness if it’s heat‑soaked or brittle—especially on the V6 where the harness lives in the hot valley. The sensor must be torqued to spec and oriented correctly so it “hears” true knock, over‑ or under‑tightening can skew readings. On the 2AZ‑FE, access is from the intake side of the block. On the 3MZ‑FE V6, the upper intake manifold has to come off, so new gaskets and a careful clean‑down are part of the job. Clear codes, verify no vacuum leaks, and confirm timing correction is behaving with a scan tool after refitting.

• Typical symptoms: check engine light (P0325/P0330), dull performance, poor economy, or audible pinging under load.
• Best practice: fix wiring issues first, use the right torque, and keep to OE‑quality parts.

FAQs

Where is the knock sensor on a 2004 Toyota Highlander?
On the 2.4L 2AZ‑FE, it’s bolted to the engine block under the intake side. On the 3.3L 3MZ‑FE V6, there are two sensors mounted in the valley between the cylinder banks under the intake manifold. Access on the V6 usually requires removing the upper intake plenum and related hardware.

What are the signs of a faulty knock sensor on this model?
Common signs include a check engine light with codes P0325 or P0330, noticeable loss of power, and higher fuel use. Sometimes there’s pinging under load, but often the ECU over‑retards timing to protect the engine, so the car just feels a bit gutless. Wiring faults and aged sub‑harnesses are frequent culprits—worth checking before replacing the sensor itself.

Is it safe to drive with a bad knock sensor?
It’ll usually still run, but the ECU may lock timing into a conservative map to avoid engine damage. That means lacklustre performance and poorer economy. Prolonged driving while ignoring genuine detonation risks piston and valve damage, so it’s best to diagnose and sort it promptly.