Climate Control A/C Post Evaporator Sensor Circuit Failure
The sensor that measures air temperature after the A/C evaporator has failed or lost connection, like a broken thermometer in your air conditioning system. Your climate control can't properly adjust cooling because it can't read the temperature downstream of the evaporator.
The ECU monitors voltage signal from the post-evaporator temperature sensor to verify proper A/C cooling performance. It compares sensor readings against expected temperature ranges and electrical signal integrity. A broken circuit, open wire, or sensor failure prevents the ECM from confirming refrigerant cooling effectiveness.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Voltage | 0.5–4.5V proportional to temperature | Out of range, shorted, or open circuit |
| Post-Evaporator Temperature | 35–50°F when A/C active | Sensor unable to read or implausible value |
Code B1946 is a low-severity fault. Your vehicle is generally safe to drive to a workshop for diagnosis. However, do not ignore it indefinitely — low-severity codes often indicate developing problems that become expensive if neglected. Book a diagnostic appointment within 2–4 weeks. If you notice any additional symptoms (rough running, power loss, unusual smells), treat it as higher priority.
Once the fault is repaired, B1946 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.