Parts for your 2018 Toyota Mark x-Throttle position sensors

2018 Toyota Mark X throttle position sensor — what it does and when to service it

The 2018 Toyota Mark X (GRX130/133, 4GR‑FSE 2.5 V6 and 2GR‑FSE 3.5 V6) absolutely uses a throttle position sensor. Toyota’s ETCS‑i electronic throttle relies on dual throttle position sensors integrated into the throttle body, alongside an accelerator pedal position sensor. This is detailed in Toyota’s Repair Manual for the Mark X engine control system (ETCS‑i for 4GR‑FSE/2GR‑FSE) and reflected in Toyota parts catalogues listing the throttle body assembly with built‑in TPS, plus fault codes P0120–P0124 and P2135 that monitor throttle position circuit performance.

On this model, the throttle position sensor (really, a pair of them) tells the engine computer exactly how far the throttle plate is open. That lets the ECU manage airflow, fuel and ignition with pinpoint accuracy for smooth take‑off, crisp response and good economy. Because the Mark X uses drive‑by‑wire, the TPS is mission‑critical — if its signals don’t make sense, the car can drop into limp mode to protect the engine and transmission.

There’s no scheduled replacement interval for the TPS on a 2018 Mark X. It’s designed to be maintenance‑free, and on these engines the sensors are built into the throttle body as a non‑serviceable assembly. If a sensor fails or goes out of correlation, the usual fix is to replace the throttle body assembly and perform a throttle/idle learn with a scan tool.

Good workshop practice during regular servicing includes checking live data with a scan tool. Look for smooth, matching “Throttle Position Sensor No.1/No.2” traces with no drop‑outs, and no stored codes like P0120, P0122, P0123, P0124, or P2135. If cleaning is needed for a sticky throttle, use throttle‑body‑safe cleaner, keep solvents off the electronics, and don’t force the plate by hand. After battery disconnection or throttle body replacement, complete the idle relearn so the Mark X settles to a steady idle.

• Signs a TPS is playing up: erratic idle, hesitation, poor kick‑down, cruise control faults, or the MIL on.
• Replacement notes: genuine or quality OEM throttle body, new gasket, torque to spec, and carry out ETCS‑i calibration.
• Pre‑emptive care: fix intake air leaks, keep the air filter fresh, and ensure good battery voltage to avoid false TPS codes.

FAQs

Does a 2018 Toyota Mark X have a throttle position sensor?

Yes. It uses dual throttle position sensors built into the electronic throttle body as part of Toyota’s ETCS‑i system on both 4GR‑FSE and 2GR‑FSE engines. They’re monitored by the ECU and aren’t separate bolt‑on sensors in this generation.

What fault codes point to a throttle position issue on a Mark X?

Common ETCS‑i codes include P0120, P0122, P0123, P0124 (TPS circuit range/performance/low/high) and P2135 (throttle/pedal position sensor correlation). If any appear, check wiring, power and grounds, then assess the throttle body assembly.

Can the TPS be replaced separately on a 2018 Mark X?

Typically no. The TPS is integrated with the throttle body. If the sensor is faulty, the usual repair is to replace the throttle body assembly, fit a new gasket, and perform throttle/idle relearn with a scan tool.