What this code means
This code may mean the climate control unit is not seeing the sunlight sensor circuit signal it expects.
What the vehicle may do
- Automatic climate control may react poorly to sunlight or cabin heat load.
- The code may be stored even when the driver does not notice an obvious climate-control complaint.
Possible fault areas
- Possible loose or poor connections in the sunlight sensor circuit.
- Possible open wiring on the sensor signal or sensor common side of the circuit.
- Possible short between related sensor circuits.
- Possible sunlight sensor or climate control unit involvement after circuit checks.
Diagnostic path
Opening context
On this Honda CR-V application, including the L4-2.4L (K24W9) engine description, B1229 points to an open in the sunlight sensor circuit for the climate control unit. In plain terms, the control unit may not be getting the sun-load signal it expects. The driver may notice the automatic climate control reacting poorly to sunlight, or the system may store the code with no obvious complaint. Broadly, this can involve wiring or connector trouble in the sunlight sensor circuit, a possible sunlight sensor issue, or a possible climate control unit issue. The diagnostic path is to confirm the code first, then work through the TSUN line, the SENSOR COM line, the short check, and finally the sensor-versus-control-unit decision.
Confirm the fault first
Start by clearing the DTC with the HDS. Turn the vehicle to OFF, LOCK mode, then turn it back ON. Run the self-diagnostic function with the HDS or with the climate control unit, then check for codes again. If B1229, or 07 on the climate display, is indicated again, continue with the circuit checks. If it is not indicated, treat it as an intermittent fault and check for loose wires or poor connections in the sunlight sensor circuit.
Check the TSUN line for an open
Next, turn the vehicle back to OFF, LOCK mode. Disconnect the climate control unit 32P connector and disconnect the sunlight sensor connector. For the TSUN continuity check, test from climate control unit 32P connector No. 3 to the sunlight sensor connector No. 2 terminal for the applicable connector setup. If there is continuity, the TSUN wire is not open, so move on to the next check. If there is no continuity, repair the open in the wire between the climate control unit and the sunlight sensor.
Check the SENSOR COM line for an open
With the vehicle still OFF, LOCK mode, and with the climate control unit 32P connector and sunlight sensor connector still disconnected, check the SENSOR COM line. Test from climate control unit 32P connector No. 23 to the sunlight sensor connector. On the 2P connector, the sunlight sensor side is No. 1. On the 7P connector, the sunlight sensor side is No. 3. If there is continuity, the SENSOR COM wire is OK and the next check is the short check. If there is no continuity, repair the open in the wire between the climate control unit and the sunlight sensor.
Check TSUN for a short to SENSOR 5V
Now check whether the TSUN line is shorted to the SENSOR 5V line. Keep the vehicle in OFF, LOCK mode, with the climate control unit 32P connector disconnected and the sunlight sensor connector disconnected. Check continuity between climate control unit 32P connector No. 3 and climate control unit 32P connector No. 17. If there is continuity, repair the short in the wires between the climate control unit and the sunlight sensor. If there is no continuity, the TSUN wire and SENSOR 5V wire are not shorted, so continue to the sunlight sensor check.
Make the sensor-versus-control-unit decision
Reconnect the climate control unit 32P connector, then test the sunlight sensor. At that point, pause and complete the correct sunlight sensor test before making the call. Do not substitute a guess for that test. If the sunlight sensor tests OK, replace the climate control unit. If the sunlight sensor does not test OK, replace the sunlight sensor.
Verify and close
Keep verification separate from the circuit testing. Once the fault path has been corrected, use the same basic confirmation routine: clear the DTC, cycle the vehicle from OFF, LOCK mode back to ON, run the self-diagnostic function, and confirm B1229 stays gone. The takeaway is simple: prove the code is current, prove both sensor wires can carry the signal, rule out the short between TSUN and the sensor power line, then make the sensor or control-unit decision only after the sunlight sensor has been tested correctly. For more diagnostic training, visit stepdiagnostics.com.
Final check
This code is often best approached by confirming the fault, proving the circuit, then making the sensor or control-unit decision.
For more guided automotive diagnostics, visit STEP Diagnostics.
