Parts for your 2002 Toyota Echo|yaris-Temperature sensors

2002 Toyota Echo/Yaris temperature sensors — purpose, care, and when to replace

Temperature sensors are absolutely fitted and relevant on the 2002 Toyota Echo/Yaris. Toyota’s 1NZ‑FE Repair Manual (Engine Control System – SFI, ECT Sensor, DTC P0115–P0119) and the 2002 Electrical Wiring Diagram detail the engine coolant temperature (ECT) sensor feeding the ECM (THW–E2) and informing the combination meter. The Haynes Yaris 1999–2005 manual also covers the ECT, the intake air temperature (IAT) thermistor integrated in the MAF sensor, and—on automatic models—the transmission fluid temperature sensor in the valve body.

On this Echo/Yaris, temperature sensors are the quiet achievers that keep it running sweet as. The ECT tells the engine computer how warm the coolant is, so it can sort cold-start enrichment, idle speed, ignition timing, radiator fan operation, and even the dash temp warning. The IAT helps trim fuelling as the outside air gets hotter or cooler. In automatic versions, the trans fluid temp sensor helps the control logic manage shift timing and converter lock-up when the fluid’s cold or working hard.

They’re not a “replace by kilometres” item, but they do age. As part of servicing, it’s smart to check for stored fault codes, inspect the ECT connector and wiring for corrosion or coolant residue, and confirm the cooling system is healthy with the correct Toyota red/pink coolant at the right mix. If starting is rough when cold, the radiator fans run when they shouldn’t, or fuel economy’s gone pear-shaped, a lazy temp sensor could be in the mix.

• Common signs: hard cold starts, rich running or high idle, erratic temp light/gauge behaviour, radiator fans stuck on/off, harsh shifts on autos, and codes like P0115–P0119.

Replacing the ECT on the 1NZ‑FE is straightforward for a competent DIYer: it lives near the thermostat housing at the cylinder head outlet. Let the engine cool, relieve system pressure, catch a small amount of coolant, unplug the two‑pin connector, swap the sensor (use the correct sealing washer/O‑ring if specified), and tighten to the workshop spec—don’t overdo it. Refit, top up with the right coolant, and bleed air properly.

The IAT sits inside the MAF on the intake duct, keep it tidy by cleaning the MAF with proper MAF cleaner only—no harsh solvents and don’t touch the sensing elements. The auto trans temp sensor is internal, so focus on fluid condition and servicing rather than pre-emptive replacement.

A quick scan with a capable OBD tool and a cooling system once-over at service time will keep these sensors doing their job across Aussie and Kiwi climates.

FAQs

Where is the engine coolant temperature (ECT) sensor on a 2002 Echo/Yaris?
It’s mounted at the coolant outlet/thermostat housing on the cylinder head, with a two‑pin connector. Access is under the bonnet from the top, on some cars, moving the intake duct gives clearer room.

Always start with a cool engine, and be ready to catch a little coolant when removing the sensor. Refill and bleed the system after refitting.

What symptoms point to a dodgy temperature sensor on this model?
Think hard cold starts, rich running, poor fuel economy, fans running when they shouldn’t, or the temp light acting oddly. The ECU often logs codes like P0115–P0119 for ECT faults.

If it’s an auto, odd shift behaviour when cold can also hint at temperature sensing issues—scan it before throwing parts.

Does the dash temp light use the same sensor as the ECU?
On this generation, the ECT sensor’s signal goes to the engine ECU, which then informs the combination meter. So the dash indication and the ECU strategy both rely on that same measured coolant temperature.

That’s why a single out‑of‑range sensor can affect both how it runs and what you see on the dash.