Barometer Pressure Circuit Malfunction
Your engine computer uses a barometer sensor to detect air pressure and adjust fuel mixture accordingly; when this sensor circuit fails, the ECU can't properly compensate for altitude changes. It's like a weather station that's broken—your engine doesn't know if it's at sea level or on a mountain.
The ECU monitors voltage from the barometric pressure sensor to determine ambient air pressure, then uses this data to calculate proper fuel injection quantity and ignition timing. The sensor typically outputs 0-5V corresponding to atmospheric pressure changes. When voltage readings fall outside expected ranges or become erratic, the ECU triggers a fault code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Barometer Sensor Voltage | 0.5-4.5V (proportional to air pressure) | Below 0.2V or above 4.8V, or no signal detected |
| Pressure Range | 10-105 kPa | Out-of-range readings or sensor dropout |
Code P1797 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1797 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.