🚨 Diagnostic Profile
Vehicle Make: Buick
Technical Description: A/C Evaporator Temperature Sensor Circuit Low Voltage
This diagnostic trouble code indicates that the Heating, Ventilation, and Air Conditioning (HVAC) control module has detected a voltage signal from the evaporator temperature sensor circuit that is lower than the expected calibrated range. The evaporator temperature sensor monitors the temperature of the A/C evaporator core to prevent icing and to regulate compressor cycling. A low voltage reading typically suggests a short to ground, a failing sensor, or a wiring/connector issue within the circuit.
🚨 Repair Difficulty Tier
Difficulty Rating: Intermediate
This repair requires the use of a digital multimeter and an OBD-II scan tool capable of reading live HVAC data streams. While no complex module programming is typically required, proper diagnosis involves checking resistance values against manufacturer specifications and verifying circuit integrity. Basic electrical diagnostic knowledge and dashboard/console disassembly skills are necessary to access the sensor.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
Begin by visually inspecting the evaporator temperature sensor connector located near the evaporator core (often accessible behind the glove box or lower dash panel). Check for:
• Corroded, bent, or damaged terminal pins
• Signs of moisture intrusion or condensation pooling near the connector
• Chafed, pinched, or frayed wiring harness leading to the sensor
• Secure and fully seated connector engagement
Also inspect the HVAC module ground connections, as a poor ground can sometimes mimic a low voltage sensor fault.
Step 2: Diagnostic Verification
Using a scan tool, access the HVAC data stream and monitor the evaporator temperature sensor’s live voltage and temperature reading. Compare the displayed temperature to actual ambient/evaporator conditions using an infrared thermometer for cross-reference.
Next, disconnect the sensor connector and use a digital multimeter to measure the resistance across the sensor terminals. Compare this reading to the manufacturer’s resistance-to-temperature chart (commonly a Negative Temperature Coefficient/NTC thermistor). If resistance is at or near zero ohms, this confirms an internal short within the sensor.
With the sensor disconnected, perform a voltage drop test at the harness connector (key on, engine off) to verify the HVAC module is supplying the correct reference voltage (typically 5V) and that there is no short to ground within the wiring harness itself.
Step 3: Resolution & Reset Process
If the sensor resistance is out of specification or shows a dead short, replace the evaporator temperature sensor with an OEM or OEM-equivalent part. If the sensor tests within range but the harness shows a short to ground, repair or replace the affected wiring section and re-insulate the repair with heat shrink tubing.
After replacement/repair, clear the stored Diagnostic Trouble Codes (DTCs) using the scan tool. Cycle the ignition and run the HVAC system through a full cooling cycle to confirm the live data stream now reflects accurate, fluctuating temperature readings without re-triggering the fault code.
📦 Parts, Labor, and Budget Estimates
Required Components/Software:
• A/C Evaporator Temperature Sensor (OEM or aftermarket equivalent)
• Wiring harness repair kit (if applicable)
• Digital Multimeter
• OBD-II Scan Tool with live HVAC data stream capability
Average Component Price: $15 – $45 USD for the sensor itself. Wiring harness repairs, if needed, typically add $20 – $50 USD in materials.
Estimated Labor Hours: 0.5 – 1.5 hours, depending on dash disassembly complexity required to access the evaporator core housing. Diagnostic time is typically billed separately at 0.5 hours if a straightforward sensor replacement resolves the fault.