Code 121, A/C High Temperature Sensor

Code will set if outside air temperature sensor failure is not indicated by PCM, outside air temperature is 4-99°C and A/C high side temperature sensor is less than -12°C or greater than 210°C.

1. Determines if conditions to set code are present.
2. With A/C high temperature sensor connector terminals jumpered together, scan should display 210°C.
3. With A/C high side temperature sensor unplugged, scan should display less than -12°C.
4. When A/C high temperature sensor signal circuit is jumpered to ground, scan should display greater than 210°C.
5. When backprobing PCM A/C high temperature sensor signal circuit to ground, scan should display greater than 210°C.

Fig 1: Code 121 Schematic (4.0L) A/C High Temperature Sensor

Fig 2: Code 121 Diagnostic Flow Chart (4.0L) A/C High Temperature Sensor