Parts for your 1999 Toyota Hilux surf-Temperature sensors

1999 Toyota Hilux Surf Temperature Sensors

Temperature sensors are absolutely fitted to the 1999 Toyota Hilux Surf. Technical sources such as the Toyota Hilux Surf/4Runner Repair Manual (1996–2002, SFI/EFI sections), the 1999 Toyota Electrical Wiring Diagram (EWD), and Toyota parts catalogues all document multiple temperature sensors on these models. That includes the engine coolant temperature (ECT) sensor for the ECU, a separate coolant temperature sender for the dash gauge, the intake air temperature (IAT) sensor (integrated with or adjacent to the airflow meter on many petrol variants), and an automatic transmission fluid temperature sensor on A340/A343-series autos. Some trims also carry A/C-related temperature sensors.

On a 1999 Hilux Surf, these sensors do a heap of behind-the-scenes work. The ECT sensor tells the ECU how warm the engine is so it can set fuel delivery, ignition timing, idle speed and glow/after-glow logic on diesels. It also influences fan and A/C behaviour on certain specs. The dash sender simply drives the coolant gauge so the driver can spot overheating before it cooks the head. The IAT sensor lets the ECU adjust fuelling for dense cold air or thin hot air, while the auto trans temp sensor helps choose shift timing and lock-up to keep the box happy.

They’re not a scheduled replacement item, but they do age. During regular servicing, it’s smart to:

• Scan for fault codes (e.g., P0115–P0119 range/performance codes) and live-data check ECT/IAT readings from cold start to operating temp.
• Inspect connectors for corrosion, brittle wiring and coolant wicking into plugs.
• Confirm the cooling system is healthy: correct coolant mix, no sludge, good cap and thermostat.

Replacement is straightforward. With the engine cold, bleed off pressure, drain a little coolant below sensor level, unplug the connector and remove the sensor with a deep socket. Fit the new sensor with the correct sealing washer or pre-coated threads, and tighten to the torque spec in the Toyota manual (do not overtighten). Refill and bleed the cooling system, then verify the new readings on a scan tool and check for leaks. On models with both an ECU sensor and a gauge sender, match the right part to the right port—one is typically a two-wire ECT for the ECU and the other a single-wire sender for the dash.

Signs of a crook temperature sensor include hard cold starts, rich running, sooty exhaust on diesels, rough idle, poor fuel economy, erratic temp gauge, or the radiator fans behaving oddly. Left unchecked, it can mask real overheating—never ideal on a long Kiwi or Aussie haul.

Where is the coolant temperature sensor on a 1999 Hilux Surf?

It’s threaded into the engine’s coolant outlet housing near the thermostat. On the 1KZ-TE diesel it sits on the water outlet at the cylinder head