What this code means
B1231 may indicate the climate control unit is seeing the evaporator temperature sensor circuit like an open or high-signal condition.
What the vehicle may do
- The A/C temperature control may be affected.
- The HVAC system can use a fallback strategy when sensor information is not trusted.
- A climate control warning or stored HVAC fault may be present.
Possible fault areas
- Possible evaporator temperature sensor signal circuit fault.
- Possible sensor-common circuit fault.
- Possible connector or terminal condition in the HVAC sensor circuit.
- Possible climate control unit fault area after the circuit checks are normal.
Diagnostic path
Set up the diagnostic direction
On this Honda CR-V, B1231 is an HVAC code for the evaporator temperature sensor circuit reading like an open circuit. In plain terms, the climate control unit may be seeing the sensor signal go higher than it should, so A/C temperature control may be affected, or the system can fall back to a default strategy. The possible fault areas are the evaporator temperature sensor signal and sensor-common circuits, their connectors, or the climate control unit itself. Before you get into the pinpoint checks, make sure the basic troubleshooting approach for this system is understood, then work the path in order. Turn the vehicle to ON mode, then use the HDS and open Body Electrical, HVAC, Data List so you can look at the HVAC data before moving into circuit testing.
Prepare for TEVA and SENS-COM circuit checks
Next, set up for the TEVA and SENS-COM circuit inspection. With the evaporator temperature sensor connector, 2P, disconnected and climate control unit connector B, 24P, disconnected, you’re isolating the wiring between the sensor side and the control unit side. That keeps the first checks focused on the circuit instead of guessing at a module or sensor right away.
Check for opens first
With IG Mode OFF, perform the TEVA open wire inspection according to the inspection table. A normal result is less than 1 Ω. Then stay in the same setup and perform the SENS-COM open wire inspection, also with IG Mode OFF. That normal result is also less than 1 Ω. If either side does not meet the open-wire check, treat that as a circuit problem and stay with the wiring and connection path.
Then check for a short to power
After the open checks, use the open-and-shorted-wire inspection method and move into the short check as conditions call for it. For TEVA shorted to power inspection, switch to IG Mode ON and inspect according to the table. The expected result is not shorted. If this check is abnormal, the diagnostic direction is still the circuit, not the climate control unit.
Only move to the climate control unit after the circuit checks pass
If the TEVA and SENS-COM circuit inspections indicate a normal condition, then move on to the climate control unit inspection. At that point, the diagnostic path treats the remaining climate control unit as the cause area. Evaluate that inspection result directly: if it fails, there is a problem with the climate control unit.
Takeaway
The key on B1231 is to prove the TEVA and SENS-COM wiring first. Less than 1 Ω is the target for the open checks, the TEVA power short check should be not shorted, and only after those circuit checks are normal should the climate control unit inspection come into play. For more diagnostic training, visit stepdiagnostics.com.
Final check
Work the circuit checks first, then move to the climate control unit inspection only if the circuit checks are normal.
For more guided automotive diagnostics, visit STEP Diagnostics.
