B0178 Possible Causes
- Faulty Output Air Temperature Sensor 2
- Output Air Temperature Sensor 2 harness is open or shorted
- Output Air Temperature Sensor 2 circuit poor electrical connection
- Faulty Heating, Ventilation, and Air Conditioning (HVAC) Control Module
First diagnose B0178 code
Check the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded terminals.
B0178 Tech NotesB0178 05: Output Air Temperature Sensor 2 Circuit Short to Battery or Open
B0178 02: Output Air Temperature Sensor 2 Circuit Short to Ground
Cost of diagnosing the B0178 code
Labor: 1.0The cost of diagnosing the B0178 code is 1.0 hour of labor. The auto repair labor rates vary widely across the country, and even within the same city. Most auto repairs shops charge between $75 and $150 per hour.
B0178 Possible Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
B0178 MeaningAir temperature sensors allow the Heating, Ventilation, and Air Conditioning (HVAC) Control Module to monitor the temperature of the discharge air in the HVAC ducts. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuit. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. When the duct air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the duct air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The HVAC control module converts the voltage values to count values where 1 volt is approximately equal to 51 counts.
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