What this code means
B1229 may mean the climate control unit is seeing an open in the sunlight sensor circuit.
What the vehicle may do
- The automatic climate control may react incorrectly to sunlight load.
- Cabin temperature control may feel inconsistent in some conditions.
Possible fault areas
- Possible sunlight sensor issue
- Possible wiring or connector issue in the sunlight sensor circuit
- Possible climate control unit circuit issue
Diagnostic path
Open and frame the fault
On this 2010 to 2017 Honda Accord with the 2.4 gas engine, B1229 in the climate control unit means the system is seeing an open in the sunlight sensor circuit. In plain language, the HVAC control may be losing the sun-load input it uses for climate decisions. The vehicle may have odd automatic climate behavior, and the possible fault areas can include the sunlight sensor, the sensor wiring and connectors, or the climate control unit side of the circuit. Start by proving whether the code is current before getting into wiring checks.
Verify whether B1229 is current
First, clear the DTC with the HDS. Then cycle the vehicle power: turn the ignition switch to LOCK (0) and back to ON (II), or use the engine start/stop button to go to OFF mode and then ON mode. Run the self-diagnostic function with the HDS or through the climate control unit, then check for DTCs. If B1229, or indicator 07, comes right back, continue with the circuit checks. If it does not come back, treat it as an intermittent fault and look closely for loose wires or poor connections in the sunlight sensor circuit.
Check the TSUN line for an open
With the fault verified, shut the vehicle back down: ignition switch at LOCK (0), or OFF mode with the start/stop button. Disconnect the climate control unit 32P connector and disconnect the sunlight sensor connector. For a vehicle without automatic lighting, the sunlight sensor connector is the 2P connector. For a vehicle with automatic lighting, it is the 7P connector. Now check continuity on the TSUN line. At the climate control unit, use 32P connector No. 25, the PUR wire. At the sunlight sensor, use No. 2, the PUR wire, whether it is the 2P connector or the 7P connector. If continuity is present, the TSUN wire is not open, so move on. If continuity is not present, repair the open between the climate control unit and the sunlight sensor.
Check the SENSOR COM line for an open
Next, keep the connectors disconnected and check the SENSOR COM line. At the climate control unit, use 32P connector No. 22, the BLU wire. Without automatic lighting, check to sunlight sensor 2P connector No. 1, the BLU wire. With automatic lighting, check to sunlight sensor 7P connector No. 3, the BLU wire. If you have continuity, the SENSOR COM wire is OK and you keep going. If you do not have continuity, repair the open between the climate control unit and the sunlight sensor.
Check for a short between TSUN and S 5V
After both open checks pass, check whether the TSUN line is shorted to the S 5V, or S5V, line. Keep the ignition at LOCK (0) or OFF mode, and keep the climate control unit 32P connector and sunlight sensor 2P or 7P connector disconnected. Check continuity between climate control unit 32P connector No. 24, the BLK wire, and No. 25, the PUR wire. If there is continuity, repair the short between the climate control unit and the sunlight sensor. If there is no continuity, the TSUN and S 5V/S5V wiring checks have passed.
Make the final component call carefully
Once the wiring checks pass, reconnect the climate control unit 32P connector and test the sunlight sensor. Do not make the final part decision until that sensor test has been completed by a known-good method. The detailed sunlight sensor test information is not included in this diagnostic path, so pause there instead of guessing. If the sunlight sensor tests OK, the next call is the climate control unit. If the sunlight sensor does not test OK, the next call is the sunlight sensor.
Close
The main idea on B1229 is simple: prove the code is current, verify the two sunlight sensor circuit paths, rule out the TSUN-to-S 5V short, and only then make the sensor-versus-control-unit decision. For more diagnostic training, visit stepdiagnostics.com.
Final check
B1229 often comes down to proving whether the fault is current, then separating wiring faults from the sunlight sensor and control unit decision.
For more guided automotive diagnostics, visit STEP Diagnostics.
