AC Post-Heater Sensor #2 Circuit Low Voltage
The body control module (BCM) or HVAC control module has detected abnormally low voltage on the signal circuit of the A/C post-heater sensor #2, indicating a short to ground. This sensor monitors the temperature of the heater core after coolant passes through it, helping regulate discharge air temperature.
1. Commonly Affected Makes
2. Most Common Causes
- Signal wire for post-heater sensor #2 shorted to ground
- Faulty A/C post-heater sensor #2 (internal short)
- Damaged, corroded, or pushed-back terminals in the sensor connector
- Faulty HVAC control module or BCM (internal short on input)
3. Symptoms You Will Notice
- Inconsistent or incorrect HVAC discharge temperature
- HVAC system may blow cold air when heat is requested
4. Step-by-Step Diagnosis
Check for technical service bulletins (TSBs) related to B2429 for your vehicle.
Visually inspect the post-heater sensor #2 connector and wiring for damage, corrosion, or shorts to ground.
Disconnect the sensor and measure resistance; compare to specifications (typically 1k-10k ohms at room temperature).
With sensor disconnected, check signal circuit voltage at the module; should be near 5V reference. If low, repair short to ground.
If wiring and sensor check out, suspect a faulty HVAC control module or BCM.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, the vehicle is generally safe to drive, but the HVAC system may not heat properly, which could be uncomfortable in cold weather.
How much does it cost to fix?▼
Repair costs range from $100 to $400, depending on whether the sensor, wiring, or control module needs replacement.