What does it mean?
B1238 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Ambient Temperature Sensor Open (High) .
Symptoms
- The displayed outside temperature reads at the very bottom of the scale or shows dashes
- The ice warning symbol appears in warm weather or never appears at all
- Automatic climate control runs hotter than requested because it believes it is freezing outside
- The AC compressor may be locked out and refuse to engage
- The ambient reading does not move at all during a drive
Likely causes
- Open in the ambient sensor signal or ground wire, letting the input float up to reference voltage
- Ambient sensor unplugged or a connector terminal backed out
- Internally open thermistor inside the ambient temperature sensor
- Corroded connector pins after exposure to water and road salt at the front of the vehicle
- Sensor pigtail damaged by stone impact or during front-end repair work
- Loss of the shared sensor ground at the module or at a harness splice
How to fix it
- Read the ambient sensor voltage and temperature in live data with the ignition on
- Jumper the two sensor connector pins together; the reading should jump to the top of the scale, proving the wiring and module are good
- If the reading does not change with the jumper, check the signal wire and the ground back to the module for an open
- Measure the sensor resistance and compare it with the thermistor table at a known temperature
- Clean or repair corroded terminals and seal the connector against water
- Replace the ambient sensor if it reads open, then confirm the display follows real outside temperature