What this code means
B1228 may indicate the climate control unit is seeing an outside air temperature sensor signal that is lower than expected, often treated as a possible short-circuit condition in a
What the vehicle may do
- Outside temperature display may be inaccurate
- HVAC operation may feel incorrect because the control unit may be working with bad outside temperature information
Possible fault areas
- Outside air temperature sensor circuit
- Sensor common circuit
- Wiring or connector short conditions
- Climate control unit as a possible remaining fault area after circuit checks
Diagnostic path
Opening context
On this 2017 to 2025 Honda CR-V with the 1.5 turbo, B1228 points to the outside air temperature sensor circuit being shorted. In plain terms, the climate control unit is seeing the sensor input voltage lower than it expects, so it flags the circuit as abnormal. The driver may notice outside temperature information or HVAC behavior that seems off, and the possible fault areas can include the outside air temperature sensor circuit, the shared sensor common side, wiring shorted together, wiring shorted to ground, connector issues, or the climate control unit itself. Start with the basic system checks before you get into pinpoint testing.
Set up the confirmation path
Turn the vehicle to ON mode. The logic behind this code is simple: if the climate control unit sees the outside air temperature sensor input voltage below the specified value, it determines there is an abnormality and stores B1228. The exact voltage value is not provided here, so do not invent a threshold. Treat this as a circuit-short diagnosis and follow the checks in order.
Isolate the sensor and control unit ends
For the TAM and SENSOR_COM shorted-wire inspection, disconnect the outside air temperature sensor 2P connector. Then disconnect climate control unit connector A, the 28P connector. At this point, make sure you have correct connector and cavity identification before probing. If the terminal views are not clear, pause and confirm the connector layout instead of guessing.
Check for TAM and SENSOR_COM shorted together
With IG Mode OFF, perform the TAM to SENSOR_COM shorted wire-to-wire inspection. A normal result is more than 1 MΩ. If this inspection is abnormal, the problem is in the circuit, so stay with the wiring and connector side of the diagnosis before blaming the control unit.
Use the short-circuit inspection method
For the shorted circuit being checked, use the standard open-or-shorted wire inspection method, then continue the inspection based on what the circuit is showing. The outside air temperature sensor test itself is not detailed here, so if that test is needed, pause and get the proper pass-fail information before making a call on the sensor.
Check TAM shorted to ground
Next, with IG Mode OFF, perform the TAM shorted-to-ground inspection. Again, the normal condition is more than 1 MΩ. If the result is abnormal, you have a circuit problem to resolve.
Control unit decision point
Only after the other inspection items indicate a normal condition does this path point to the remaining climate control unit as the cause. In other words, do not jump there first. Prove the outside air temperature sensor wiring checks are normal, then make the control unit decision.
Takeaway
The takeaway for B1228 is to treat it as a low-input short-circuit fault on the outside air temperature sensor path: isolate the sensor and climate control unit, check TAM against SENSOR_COM, check TAM to ground, and only consider the climate control unit after the circuit checks normal. For more diagnostic training, visit stepdiagnostics.com.
Final check
B1228 can involve the outside air temperature sensor signal path, so the diagnosis should focus on proving whether the circuit is shorted before considering the climate control unit.
For more guided automotive diagnostics, visit STEP Diagnostics.
