What this code means
B1228 may indicate that the climate control unit is seeing a possible short in the outside air temperature sensor circuit.
What the vehicle may do
- The outside temperature reading may be incorrect or unavailable.
- Automatic climate control behavior may seem off because the system can use outside temperature information as part of its strategy.
Possible fault areas
- The outside air temperature sensor may be involved.
- The sensor connector or wiring may have a poor connection or possible short to ground.
- The TAM circuit may be involved.
- The climate control unit can be a possible fault area after the sensor and wiring checks are completed.
Diagnostic path
Code overview
On a 2010-2015 Honda Civic with the 1.8 L engine, B1228 points us toward the climate control unit seeing a possible short in the outside air temperature sensor circuit. The driver may notice the outside temperature reading or climate control behavior acting wrong, but the diagnostic path is still straightforward: verify the code, check the outside air temperature sensor, then check the TAM circuit for a short to body ground before condemning the control unit.
Verify the fault first
Start by verifying the problem. Clear the DTC with the HDS. Turn the ignition switch to LOCK (0), then back to ON (II). Run the self-diagnostic with the HDS or through the climate control unit, then check for DTCs. If B1228 is indicated again, continue to the outside air temperature sensor check. If it does not come back, treat it as an intermittent failure and check for loose wires or poor connections in the outside air temperature circuit.
Check the outside air temperature sensor
Next, turn the ignition switch to LOCK (0). Remove the outside air temperature sensor and test it. If the sensor tests OK, leave the outside air temperature sensor disconnected and move on to the shorted-wire check. If the sensor does not test OK, replace the outside air temperature sensor.
Check the TAM wire for a short to ground
For the circuit check, keep the ignition at LOCK (0). Disconnect the climate control unit 32P connector, and make sure the outside air temperature sensor 2P connector is still disconnected. Check continuity on the TAM circuit between climate control unit 32P connector No. 18, the BLU wire, and body ground. If there is continuity, repair the short to body ground in the wire between the climate control unit and the outside air temperature sensor. If there is no continuity, the TAM wire is OK, and the diagnostic path calls for replacing the climate control unit.
Verify the repair
After the repair, use the same code-clearing and self-diagnostic check from the beginning of the test. Confirm B1228 does not return. The key takeaway is not to jump straight to the control unit: prove the fault, test the sensor, check the TAM wire for a short to body ground, and only then make the final call. For more diagnostic training, visit stepdiagnostics.com.
Final check
A calm diagnostic path may isolate whether the issue is the sensor, wiring, or climate control unit without guessing.
For more guided automotive diagnostics, visit STEP Diagnostics.
