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Home >> Lexus >> 1995 >> SC 400 >> Repair and Diagnosis >> Heating, Ventilation & A/C (HVAC) >> HVAC Control Systems >> A/C-Heater System >> Trouble Shooting >> Code 12: - Ambient Temperature Sensor Circuit >> Sensor Resistance Test
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Sensor Resistance Test

  1. Remove engine undercover. Unplug ambient temperature sensor. Measure resistance between sensor terminals while heating sensor. See AMBIENT TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS  table.
  2. If resistance is not as specified, replace sensor. If resistance is within specification, inspect wiring harness and connectors between sensor and A/C-heater control panel. Repair as necessary. If wiring harness and connectors are okay, temporarily substitute a known-good A/C-heater control panel, then retest system.
AMBIENT TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS

Sensor Temperature °F (°C) (1) Ohms
77 (25) 1600-1800
122 (50) 500-700
(1) As temperature increases, resistance should gradually decrease.