What this code means
B1228 may mean the climate control unit is seeing a low outside air temperature sensor input.
What the vehicle may do
- The vehicle may show incorrect outside temperature information.
- Automatic climate control behavior may seem unusual or inconsistent.
Possible fault areas
- Possible outside air temperature sensor circuit issue.
- Possible connector or wiring concern between the sensor and climate control unit.
- Possible climate control unit fault area after the circuit checks normal.
Diagnostic path
Opening context
On this Civic, B1228 is a climate control code tied to the outside air temperature sensor signal. In plain terms, the climate control unit may be seeing that sensor input lower than it expects. The driver may notice incorrect outside temperature information or climate control behavior that seems off. The broad fault areas are the outside air temperature sensor circuit, connector or wiring issues, and, if the circuit checks good, a possible climate control unit fault. Start with the basic system checks before going into the circuit test.
Set up the vehicle and connectors
Begin by turning the vehicle to ON mode. For the TAM and SENSOR_COM shorted-wire inspection setup, disconnect the outside air temperature sensor 2P connector, then disconnect climate control unit connector A, the 28P connector.
Check the TAM and SENSOR_COM circuit for a short
Now perform the TAM and SENSOR_COM shorted-wire inspection at the disconnected climate control unit connector A female terminals. The normal wire-to-wire result, with IG Mode OFF, is more than 1 MΩ. For TAM shorted to ground, with IG Mode OFF, the normal result is not shorted. If the exact terminal path is not clear from the connector information available at the vehicle, pause and recheck the circuit identification before testing. Do not guess on terminal locations.
Interpret the circuit result
Evaluate the shorted-wire inspection results before moving on. If that TAM or SENSOR_COM inspection is abnormal, treat it as a circuit problem. Stay with the wiring and connector side of the diagnosis until that abnormal circuit condition is found and corrected.
Only then judge the control unit
Only perform the climate control unit inspection after the other inspection items have shown normal results. If the circuit side checks normal, the remaining fault area is the climate control unit itself. This path does not support jumping straight to the unit before the sensor circuit checks are handled.
Takeaway
The key on B1228 is to prove the outside air temperature sensor circuit first: set up the disconnected connectors, check TAM and SENSOR_COM for shorts using the specified normal results, and only consider the climate control unit after the other checks are normal. For more diagnostic training, visit stepdiagnostics.com.
Final check
This code is often approached by proving the outside air temperature sensor circuit first, then considering the climate control unit only if the related circuit checks are normal.
For more guided automotive diagnostics, visit STEP Diagnostics.
