B0166 code meaning
HVAC Discharge Air Temperature Sensor
What B0166 means
The public J2012 lists do not contain B0166, and no make describes it as a discharge air sensor. Saab does use it, for the cabin rather than the outlet: in 9-3 climate control manuals from 2003 to 2012, B0166 05 marks the indoor or compartment temperature sensor as open or shorted to supply once the module input rises above 4.8 V, checked continuously with the ignition on; B0165 02 is the matching short to ground. Discharge or duct air sensors are NTC thermistors in the outlet ducts that let the module check what it actually delivers. GM's Global A system, per the 2011 Saab 9-5 manual, numbers them B0173, B0178, B0509 and B0514. A B0166 therefore needs the make's own definition.
B0166 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of B0166
- Automatic climate control misjudges cabin or outlet temperature and over- or undercorrects
- Set temperature is not held steadily
Common causes of B0166
- Most likelySensor open or signal shorted to supply (Saab 9-3 cabin sensor)
- PossibleSensor connector loose or left unplugged after dashboard work
- Less likelyOn other makes, the outlet duct sensor itself failed
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Discharge air temp sensorIn vehicle temperature sensorHvac control module
What each part of B0166 means
| B | Body system: airbags, seat belts, power seats, lights and climate control. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 66 | The exact fault in that area. |
What to do next
- Note B0166 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about B0166
What does B0166 mean?
B0166 means "HVAC Discharge Air Temperature Sensor". The public J2012 lists do not contain B0166, and no make describes it as a discharge air sensor. It is a generic code, so it means the same on every make.
Is it safe to drive with B0166?
B0166 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will B0166 fail an emissions test?
B0166 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is B0166 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will B0166 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.