What does it mean?
P1794 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T Barometric Pressure Sensor Circuit Malfunction .
Symptoms
- MIL (check engine lamp) is on and shift points are noticeably off, particularly at altitude
- Harsh or unusually early shifts, or shifts that feel soft under load
- Reduced engine power and slower response when pulling away
- Fuel consumption climbs
- The transmission may enter limp mode
- Behaviour changes markedly between low ground and mountain roads
Likely causes
- Barometric pressure sensor failed or drifted, whether standalone or integrated into another sensor
- Corroded connector or a broken signal, reference or ground wire
- Blocked or contaminated sensor vent or port
- A faulty manifold pressure sensor on systems that derive barometric pressure from it at key-on
- An implausible reading stored at key-on because the engine was cranking or already running when the module sampled it
- Water ingress into the sensor or its connector
- Control module input circuit fault
How to fix it
- With the ignition on and the engine off, read the barometric value in live data and compare it with local atmospheric pressure for your altitude
- On systems that share the reading, compare barometric and manifold pressure with the engine off; they should be nearly identical
- Check the sensor connector for corrosion, moisture and terminal tension
- Measure the reference voltage, ground and signal at the sensor with the ignition on
- Check the sensor port or vent for blockage and clean it if necessary
- Replace the sensor once the wiring is verified, then confirm the value reads correctly at key-on