Parts for your 2004 Toyota Mark x-Knock sensor

2004 Toyota Mark X Knock Sensor — What It Does and When To Replace It

Yes, the 2004 Toyota Mark X is fitted with knock sensors. Both the 4GR-FSE (2.5 L) and 3GR-FSE (3.0 L) V6 engines used in the GRX120 series run twin piezoelectric knock sensors—one per bank—mounted in the V of the block. This is documented in Toyota’s Mark X repair manual for the GRX120/121 series (Engine Control – Knock Sensor diagnostics and DTC chart listing P0325/P0330) and reflected in the Toyota Electronic Parts Catalogue, which lists “Sensor, Knock” for these engines. That makes the knock sensor directly relevant to anyone servicing or troubleshooting a 2004 Mark X.

The knock sensor’s job is to listen for detonation (that sharp, metallic “ping” under load) and tell the ECU to tweak ignition timing and, if needed, fuelling to protect the engine. On the 2004 Mark X’s direct-injected GR engines, accurate knock feedback lets the ECU run optimum timing for power and economy on Aussie and Kiwi pump petrol, without risking damage on hot days or under heavy throttle.

It’s not a routine service item, but it’s absolutely worth a check during bigger jobs—especially anything that involves lifting the intake manifold. Typical signs the sensor or its wiring needs attention include a Check Engine Light with codes P0325 (Bank 1) or P0330 (Bank 2), a sudden loss of grunt as timing is pulled back, rough running, or poor fuel economy. Actual audible pinging can happen too, but often the ECU catches knock before it’s heard.

• Location: Two sensors live beneath the intake manifold, bolted to the block in the valley—one per bank.
• Replacement approach: Best done when the intake is already off. Always inspect the sub-loom, heat soak can make the wiring brittle.
• Fitting tips: Use a quality sensor (genuine or reputable aftermarket), clean the mounting surface, and torque to spec (about 20 N·m, confirm in service data). Don’t over-tighten.
• Good practice: Replace intake manifold gaskets, check earths, clear codes, and perform an ECU relearn after refit. Use the correct octane fuel going forward.

There’s no cleaning procedure—the sensor is sealed. If fault codes persist after wiring checks and proper torque, replacement is the fix. When healthy, the knock sensors quietly keep the GR engine safe and lively across many thousands of kilometres.

Popular questions about 2004 Toyota Mark X knock sensors

Where are the knock sensors on a 2004 Mark X?
They’re bolted to the engine block in the V under the intake manifold—one for each bank. Access usually means removing the manifold and associated plumbing, so many techs time sensor replacement with intake gasket or injector service to save labour.

What symptoms show a bad knock sensor on a Mark X?
Common clues are a Check Engine Light with P0325 or P0330, flat performance as the ECU retards timing, and higher fuel use. In some cases there’s light pinging under load, but often the ECU masks it. Always check the sensor sub-loom and connectors before calling the sensor itself.

Can a knock sensor be cleaned or reset?
No—these are sealed piezo units. If the mounting surface is clean, the bolt is torqued correctly, and the wiring is sound, a persistent fault points to replacement. After repair, clear codes and let the ECU relearn trims with a decent drive cycle.