What Does B1966 Mean?
This code indicates the Body Control Module (BCM) or Climate Control Module has detected an electrical fault in the post-heater sensor circuit of the HVAC system. The post-heater sensor monitors air temperature after passing through the heater core to ensure proper cabin heating performance. The fault may be an open circuit, short circuit, or sensor signal out of expected range.
Common Causes
35%
Faulty post-heater temperature sensor with internal failure or degraded sensing element
30%
Damaged or corroded wiring harness between BCM and post-heater sensor
20%
Loose or corroded electrical connector at post-heater sensor
15%
Failed Body Control Module or climate control module with faulty sensor input circuit
Diagnostic Steps
1
Step 1: Locate the post-heater temperature sensor (typically in HVAC housing after heater core). Visually inspect sensor and connector for physical damage, corrosion, moisture intrusion, or loose connections. Check for melted plastic or burnt terminals.
2
Step 2: Using a digital multimeter, backprobe the sensor connector with ignition on and measure voltage on signal wire (typically 5V reference) and verify ground circuit has less than 0.1V resistance to chassis ground.
3
Step 3: Disconnect sensor connector and measure sensor resistance with multimeter at ambient temperature. Compare reading to manufacturer specifications (typically 2-3k ohms at 70°F, varying with temperature). If out of range, sensor is faulty.
4
Step 4: Check wiring continuity between sensor connector and BCM/climate control module using wiring diagram. Test for shorts to ground or power, and verify no excessive resistance (should be less than 5 ohms on signal and ground wires).
5
Step 5: If sensor and wiring test good, connect a known-good post-heater sensor or use a resistor simulator matching specification to verify BCM/climate module can properly read sensor signal. If code persists, module may be faulty.
6
Step 6: After repairs, clear codes, cycle ignition, operate HVAC system through all modes and temperature settings for 5-10 minutes, then rescan to confirm no code return.
Estimated Repair Cost
$120 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) or Climate Control Module has detected an electrical fault in the post-heater sensor circuit of the HVAC system. The post-heater sensor monitors air temperature after passing through the heater core to ensure proper cabin heating performance. The fau...
The most common cause of B1966 (A/C Post Heater Sensor Circuit Failure) is: Faulty post-heater temperature sensor with internal failure or degraded sensing element
Typical repair costs for B1966 range from $120 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive as this only affects cabin heating performance monitoring and does not impact vehicle operation or safety systems. Repair at convenience, though HVAC temperature control accuracy may be compromised in cold weather.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1966 to identify the root cause.
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Quick Info
Category
Body
System
HVAC Climate Control System
Difficulty
Type
Manufacturer
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