Parts for your 1991 Toyota Hilux surf-Temperature sensors

1991 Toyota Hilux Surf temperature sensors — what they do and how to look after them

Temperature sensors are absolutely fitted to the 1991 Toyota Hilux Surf and they matter a lot. Toyota’s factory service material for these models shows multiple thermistors and senders feeding the engine ECU and instruments — including the engine coolant temperature (ECT) sensor, the dash gauge sender, intake air temperature inside the airflow meter on petrol engines, diesel fuel and coolant temp inputs on 2L-TE models, and an ATF temp sensor on autos (Toyota Factory Service Manual, Engine Control – EFI, Toyota Electrical Wiring Diagram for Hilux/4Runner, DENSO EFI training guides).

On this Surf, the ECT sensor is the big player. It tells the ECU how hot the engine is so fuelling and ignition (or injection timing on diesels) suit the conditions. Cold start enrichment, idle speed, glow control timing on 2L-TE diesels, and even auto shift logic all lean on accurate temperature data. There’s also a separate sender for the dash gauge so the driver can see what’s happening under the bonnet.

When an ECT or related sensor starts going off, owners may cop hard cold starts, rich running, black smoke (diesel), high fuel use, rough idle, lazy shifts on autos, or a gauge that’s not believable. The ECU on these OBD1-era Surfs can flash fault codes (often Code 22 for coolant temp) via the check engine lamp when TE1 and E1 are bridged — a dead handy bit of old-school diagnostics noted in Toyota’s FSM.

Maintenance-wise, temperature sensors aren’t a scheduled replacement item, but they do appreciate a bit of care:

• Keep electrical connectors clean and snug, brittle plugs are common with age.
• Protect the loom from heat soak and chafe near the thermostat housing and intake duct.
• Maintain fresh coolant — corrosion can foul sensor tips and skew readings.
• On petrol models, avoid oiled filters that can contaminate the airflow meter and its intake air temp thermistor.

Testing is simple with a multimeter: the ECT sensor’s resistance should drop smoothly as temperature rises, tracking the chart in the FSM (roughly a few kilo-ohms cold, a few hundred ohms hot). If it’s erratic or out-of-range, replace it. Swapping an ECT sensor is a straightforward spanner job: work on a cool engine, catch any coolant, unscrew the old two-pin sensor, fit the new one with the correct sealing method, snug to the factory torque, reconnect, then top up and bleed the cooling system. For the gauge sender (single wire), the drill’s similar. When in doubt, follow the Toyota specs — they’re there for a reason and keep these tough trucks running sweet as across Aussie and Kiwi kilometres.

Popular questions

Where is the coolant temperature sensor on a 1991 Hilux Surf?
It’s typically threaded into the coolant outlet near the thermostat housing on the intake side of the engine. You’ll also see a separate, single-wire sender nearby for the dash gauge. On petrol 22R-E and 3VZ-E, look around the front/top coolant neck, on 2L-TE diesels, it’s on the water outlet at the head.

What are the symptoms of a failing temp sensor on these models?
Common giveaways include hard cold starts, rich running, poor economy, rough idle, sooty exhaust on diesels, odd auto shift behaviour, and a check engine light with Code 22. If the dash gauge sender fails, the gauge reads low, high, or dead while the engine otherwise runs normally.

How do you test the ECT sensor at home?
Unplug the two-pin sensor and measure resistance across the sensor with a multimeter. Compare the values to the Toyota chart: high resistance when cold, lower when hot, changing smoothly as it warms. Any big mismatch or jumpiness points to a dud sensor or wiring. Always confirm good grounds and clean connectors before replacing parts.