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Condition Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set. Cause The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface. Correction Measure AC voltage and clean the wheel speed sensor mounting surfaces. 1. 2. 3. 4. Raise and support the vehicle. Disconnect both the front wheel speed sensor connectors at the frame and harness. Place a Digital Volt Meter (DVM) across the terminals of each wheel speed sensor connector. Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV’s. If the reading is less than 350 ACmV’s, remove the wheel speed sensor. 5. Plug the wheel speed sensor bore in order to prevent debris from falling into the hub during service. 6. Clean the wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, scotch brite, or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion. 7. Check the sensor head to determine if it has been warped/distorted due to the corrosion build up or other causes. Check the mounting surface on the sensor head for flatness by placing it on the edge of a metal machinists scale or other suitable straight edge to measure the flatness. Check the sensor for flatness in multiple (minimum 3) positions/directions. If the sensor head is distorted, replace the sensor. 8. Apply (spray) two thin coats of the specified rust penetrating lubricant (corrosion inhibitor) to the complete sensor mounting surface on the bearing hub. Allow to dry for 3-5 minutes between coats. Use ONLY Rust Penetrating Lubricant, P/N 89022217 (in Canada, P/N 89022218). 9. When the corrosion inhibitor is dry to the touch (about 10 minutes), apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (in Canada, P/N 993037). 10.Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual. 11.Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV’s.

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Cooling Fan Control The purpose of the Electro-Viscous (EV) fan clutch is to maintain powertrain cooling requirements. The Powertrain Control Module (PCM) monitors the following sensors to regulate the fan speed; – Engine coolant temperature sensor – A/C refrigerant pressure sensor – Vehicle speed sensor – Intake air temperature sensor – Transmission fluid temperature sensor – Ambient air temperature sensor The PCM controls the electro-viscous fan clutch engagement. The PCM regulates a 12-volt pulse width modulated signal (PWM) to the cooling fan relay. The PWM signal determines the ON time of the relay. As the commanded state of the fan clutch increases, so does the ON time of the relay. This ON time directly effects the amount of time the solenoid, which is internal to the fan clutch, is energized. When the solenoid in the fan clutch is energized, it opens the spring loaded valve and allows fluid to flow from the storage chamber to the fluid coupling of the cooling fan clutch, increasing the fan speed. When the solenoid is de-energized, the spring loaded valve closes, and blocks the path of the fluid to the fluid coupling of the fan clutch, reducing fan speed. The fan has the ability to create a feedback signal, so the PCM has an actual fan speed input. This is done with a hall effect sensor internal to the fan clutch. The PCM supplies a 5-volt reference and a low reference to the hall effect sensor. The hall effect sensor returns a signal pulse through the cooling fan speed signal circuit in response to the reluctor track passing by the magnetic field of the hall effect sensor. The PCM commands the cooling fan to 100% under the following conditions: – Engine coolant temperature exceeds approximately 129°C (264°F). – The transmission oil temperature exceeds approximately 151°C (304°F). – A/C refrigerant pressure exceeds 1655 kPa (240 psi). – When certain DTC’s set. These include P0116, P0117, P0118, P0125, P1481, P1482, and P1484.

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Exploded View Removal 1. Remove the intake manifold cover. 2.
Disconnect the intake air temperature (IAT) sensor 2 connector (A), and remove the breather pipe (B), then remove the intake air duct (C). 3. Remove the positive crankcase ventilation (PCV) hose (A), brake booster vacuum hose (B), vacuum hose (C) and vacuum line mounting bolts (D). 4. Remove the evaporative emission (EVAP) canister hose (A) and the transmission breather hose clamp bracket (B). 5. Remove and plug the water bypass hoses (C). 6. Remove the engine wire harness connectors and wire harness clamps from the intake manifold. Intake air temperature (IAT) sensor 1 connector Throttle actuator connector Manifold absolute pressure (MAP) sensor connector Evaporative emission (EVAP) canister purge valve connector Intake manifold tuning (IMT) (intake manifold runner control (IMRC)) actuator connector

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Room temperature sensor circuit Ambient temperature sensor circuit Evaporator temperature sensor circuit Engine coolant temperature commu- nication circuit Solar sensor circuit (short) (Passenger side) Solar sensor circuit (open) Compressor lock sensor circuit Pressure switch circuit Solar sensor circuit (short) (Driver side) Solar sensor circuit (open) Air mix damper position sensor circuit (Passenger side) Air inlet damper position sensor circuit Air outlet damper position sensor circuit 2003 4RUNNER REPAIR MANUAL (RM1001U) Air mix damper position sensor circuit (Driver side) Air mix damper control servomotor (Passenger side) Air inlet damper control servomotor Air outlet damper control servomotor Air mix damper control servomotor (Driver side)

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Air Quality Sensor At center front of engine compartment. Camshaft Position Sensor On rear of cylinder head. See Fig. 1 . Chassis Acceleration Sensor At right rear side of engine compartment. Crankshaft Position Sensor On left front side of transaxle. See Fig. 1 . Engine Coolant Temperature On top rear of engine, near thermostat. See Fig. 1 . Sensor Fuel Tank Unit On top of fuel tank, below rear seat cushion. Hot Film Airflow Sensor On end of air intake hose, at air cleaner housing. See Fig. 1 . Knock Sensor Near center rear of engine compartment, on intake manifold support bracket. O2 Sensor (Down) On front exhaust pipe, downstream of warm-up TWC converter. O2 Sensor (Up) On exhaust manifold, upstream of warm-up TWC converter. Speed Sensor On top of transaxle. Thermocon Behind glove box, on HVAC assembly. See Fig. 2 . Throttle Position Sensor On throttle body. See Fig. 1 . Turbine Sensor (A/T) On top rear of transaxle. Wheel Speed Sensor (Left Front) Attached to left front hub spindle. Wheel Speed Sensor (Left Rear) Attached to left rear hub spindle. Wheel Speed Sensor (Right Attached to right front hub spindle. Front) Wheel Speed Sensor (Right Rear) Attached to right rear hub spindle.