P0125 – Coolant temperature too low for closed-loop fuel control

System: Engine - ECT
Dashboard light: High coolant temperature light · Check engine light (MIL) · Low coolant temperature light (blue)
Check-engine blink code: —
Applies to: 1SZ-FE (by platform)
Description: Coolant temperature too low for closed-loop fuel control
Possible causes: Trouble area: 1.Thermostat stuck open 2.Coolant temperature sensor 3.Oxygen sensor circuit
What to check: Checking points: 1.Check thermostat 2.Check coolant temperature sensor 3.Check oxygen sensor
Confidence: medium (Toyota Echo 1999–2002 factory diagnostics, same XP10 platform; not confirmed on JDM 1SZ-FE)

From the factory service material. Clear the code and test-drive to confirm it returns. Search all fault codes · Common problems · Warning lights