Parts for your 2012 Toyota Mark x-Throttle position sensors

2012 Toyota Mark X throttle position sensors (TPS): what they do and how to look after them

Yes, the 2012 Toyota Mark X uses throttle position sensors. Toyota’s GRX13# Mark X Repair Manual (Engine Control – SFI System – ETCS‑i) and the Toyota Electrical Wiring Diagram show an electronically controlled throttle body with a built‑in motor and dual internal throttle position sensors (often labelled VTA1 and VTA2). The ECM monitors these against each other, and the factory diagnostic list includes TPS‑related DTCs such as P0120–P0124 and P2135, which confirms their presence. On this model, the TPS isn’t a separate bolt‑on item, it’s integrated into the throttle body assembly.

On a 2012 Mark X, the TPS tells the engine computer exactly how far the throttle plate is open. That info, paired with the accelerator pedal sensors, lets the ECM manage air, fuel and spark for smooth take‑offs, tidy gear changes and stable idle. Because the sensors are inside the throttle body, they’re protected and precisely aligned – which is great for reliability – but it also means replacement usually involves swapping the complete throttle body if a sensor fails.

As part of routine servicing, it’s wise to give the throttle body a gentle clean every 60–100,000 km, especially if the idle’s a bit lumpy or there’s a lazy throttle feel. Use a proper throttle‑body cleaner, ignition off, and avoid forcing the plate open – it’s driven by the motor. A light clean of the bore and edges of the plate can stop it sticking and keep the sensor readings consistent. While you’re there, check the connector and loom for corrosion or chafing, dodgy wiring can mimic a bad sensor.

If replacement is needed, expect to fit a complete throttle body with a fresh gasket. After refit, the ECM will generally relearn idle and throttle angles during a short drive cycle, a scan tool can speed this up and confirm the two internal sensor signals track smoothly and agree with each other. Signs it’s time to act include erratic idle, hesitation, limp mode, or the MIL on with codes like P0121, P0123 or P2135. Ignoring those can lead to poor economy and uneven performance, so it’s worth sorting promptly.

• Common symptoms: rough idle, flat spots, throttle surge, MIL on with TPS or correlation codes.
• Good practice: clean throttle body carefully, inspect wiring, and use a scan tool to verify sensor tracking.
• Replacement: throttle body assembly swap, perform idle/throttle relearn afterwards.

Popular questions

Does the 2012 Mark X have a separate TPS or is it part of the throttle body?
It’s built into the electronic throttle body along with the motor. Toyota designed it as a paired set of sensors (redundant signals) for safety and accuracy, so you don’t normally replace the TPS on its own. If a sensor fails or goes out of range, the fix is typically a complete throttle body.

What symptoms or fault codes point to a failing TPS on a Mark X?
Drivers often notice erratic idle, hesitation, poor throttle response or limp mode. The check engine light may log codes such as P0121, P0122, P0123, P0124 or P2135 (throttle/pedal position correlation). These are documented in Toyota’s Mark X diagnostic procedures and relate to the throttle angle signals the ECM expects to see.

Can the TPS be cleaned or calibrated on its own?
The sensors themselves aren’t serviceable or adjustable. Cleaning the throttle body can help if carbon buildup is causing sticking or minor drift, and the ECM will relearn after cleaning or battery disconnection. If readings are erratic or the signals don’t correlate, the proper repair is replacement of the throttle body assembly and a relearn with a scan tool if needed.