What this code means
B1228 may indicate that the climate control unit is seeing an outside air temperature sensor input that is lower than expected, consistent with a possible short in that circuit.
What the vehicle may do
- The outside temperature information may be incorrect.
- Automatic climate control operation may not match actual conditions.
- The code may remain stored until the circuit concern is addressed.
Possible fault areas
- Outside air temperature sensor circuit wiring may be shorted.
- Connector condition or terminal contact may be involved.
- The climate control unit input side may be involved after the circuit checks normal.
Diagnostic path
What B1228 is telling you
On this Civic, B1228 is a climate control code for a possible short in the outside air temperature sensor circuit. In plain terms, the climate control unit may be seeing the outside air temperature sensor signal pulled lower than it expects. The driver may notice incorrect outside temperature information or automatic climate behavior that does not match conditions. The broad fault areas are the outside air temperature sensor circuit wiring, connector condition, and the climate control unit input side. The setting logic is simple: if the input voltage from the outside air temperature sensor is less than the specified value, the climate control unit determines there is an abnormality and stores B1228.
Start clean before testing
Before getting into the circuit checks, start with the basic troubleshooting process. Do not skip the setup work, because this diagnosis depends on isolating the outside air temperature sensor circuit from the climate control unit. Turn the vehicle to ON mode. Then, for the TAM and SENSOR_COM shorted-wire inspection preparation, disconnect the outside air temperature sensor 2P connector. After that, disconnect climate control unit connector A, the 28P connector.
Check for a wire-to-wire short
With the circuit isolated, perform the TAM and SENSOR_COM shorted wire-to-wire inspection with IG Mode OFF. The normal result is more than 1 MΩ. If the reading is not normal, stay on the circuit side of the diagnosis, because the path is pointing to a wiring or circuit problem, not a control unit decision yet. For this part of the test, do not guess at meter lead placement. If the exact terminal identification for the table is not clear, stop and identify the terminals correctly before measuring.
Check for a short to ground
Next, perform the TAM short-to-ground inspection with IG Mode OFF. The expected result is not shorted. If this inspection is abnormal, treat it as a circuit problem and keep tracing the shorted condition in the outside air temperature sensor signal side before moving on.
When the circuit checks normal
Only after the other inspection items indicate a normal condition does the diagnostic path point to the remaining climate control unit as the cause. The takeaway is to prove the outside air temperature sensor circuit first: isolate the connectors, check for the wire-to-wire short, check for the short to ground, and only then let the result point back at the climate control unit. For more diagnostic training, visit stepdiagnostics.com.
Final check
This diagnosis is about proving the outside air temperature sensor circuit before blaming the climate control unit.
For more guided automotive diagnostics, visit STEP Diagnostics.
