Parts for your 1999 Toyota Rav4-Temperature sensors

1999 Toyota RAV4 temperature sensors — what they do and how to keep them sweet

Temperature sensors are absolutely fitted to the 1999 Toyota RAV4 and they’re critical to how the vehicle runs. Toyota’s factory service documentation for the 1996–2000 RAV4 (Engine Control System) specifies an Engine Coolant Temperature (ECT) sensor used by the ECU for fuelling, ignition timing, and radiator fan control, with diagnostics covering DTCs P0115–P0118 and P0125. The Electrical Wiring Diagram for 1999 also shows a separate single‑wire sender for the dash gauge, plus an Intake Air Temperature (IAT) thermistor integrated with the mass air flow meter on many models. Haynes’ RAV4 repair manual backs this up and adds that automatic transmissions include an ATF temperature sensor inside the transmission for shift strategy. So yes, temperature sensors are relevant and very much used on this model.

On a 1999 RAV4, the key temperature sensors are:

• Engine Coolant Temperature (ECT) sensor: two‑pin thermistor in the thermostat housing or cylinder head, feeding the ECU.
• Coolant temp sender (gauge): single‑wire unit for the dash gauge.
• Intake Air Temperature (IAT): typically built into the MAF on the airbox/duct.
• Automatic transmission fluid temperature sensor (autos): internal to the transmission.
• Air‑conditioning thermistors (evaporator/ambient): for A/C operation and compressor protection.

Why they matter: the ECT and IAT tell the ECU how warm the engine and intake charge are, so it can set mixtures and timing, control idle, and switch the fans. A crook sensor can cause hard cold starts, rough idle, poor economy, soot, or fans running all the time. The gauge sender affects only the dash needle