CAT Engine 2743 Fault Code: Atmospheric Pressure open/short to +batt
Also called Atmos Press Open/Short to Batt+, Atmosperic Pressure Sensor : Voltage Above Normal, Atmospheric Pressure Open/Short to +Batt, Atmospheric Pressure Open/Short to Batt+, Atmospheric Pressure Sensor : Voltage Above Normal, Atmospheric Pressure Sensor Voltage Above Normal, Atmospheric Pressure Sensor voltage above normal, Atmospheric Pressure Sensor: Voltage Above Normal, Atmospheric Pressure Sensor:Voltage Above Normal, Barometric Pressure : Voltage Above Normal
Atmospheric Pressure open/short to +batt · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 2743 (SPN 274, FMI 3) means the ECM sees the atmospheric pressure sensor signal reading above 4.8 volts DC, which the ECM reads as a short to battery voltage. The engine substitutes another sensor for atmospheric pressure and cuts power to protect itself. It affects C10 through C32 engines and is a moderate priority fix since it triggers a power derate, not an immediate shutdown.
Medium severity. This code does not stop the engine, but it forces a power derate that can reach 24 percent plus a 20 percent filter derate, for a combined 44 percent loss of power in some cases. Left unresolved, the machine will run persistently underpowered, especially at altitude, so it should be diagnosed within the shift rather than ignored.
What does CAT Engine error code 2743 mean?
Code 2743 means the ECM's atmospheric pressure sensor circuit is reading a voltage above the normal operating range, specifically above 4.8 volts DC. The ECM interprets this as a short to battery voltage on the signal wire, not a real pressure reading.
The atmospheric pressure sensor tells the ECM what the outside air pressure is so the engine can adjust power output correctly, especially at higher elevations. When this signal fails, the ECM cannot trust it and falls back on other sensors or a default value to keep the engine running, but with reduced power.
If both the atmospheric pressure sensor and the turbo compressor inlet pressure sensor (used as a backup) are out of normal range at the same time, the ECM applies a heavier combined derate. This is the engine's way of protecting itself when it can't verify actual atmospheric conditions.
What triggers a CAT Engine 2743 code?
The ECM sets this code when it reads atmospheric pressure sensor signal voltage above 4.8 volts DC. Depending on the specific ECM software, this must persist for one second, eight seconds, or thirty seconds, and the ECM must have been powered for at least two seconds, three seconds, or five seconds before the fault can log, depending on the calibration variant in use. Once confirmed, the ECM flags atmospheric pressure as invalid and substitutes a default value of 45 kPa (6.5 psi) or 100 kPa (14.5 to 15 psi), depending on the software version.
Common causes of 2743
- Leaks in the sensor's pneumatic or wiring system
- Atmospheric pressure sensor has failed internally and needs replacement
- Damaged, corroded, or loose connector pins and sockets
- Chafed, pinched, or corroded wiring in the harness between the sensor and ECM
- Incorrect sensor installed for this application
- Short circuit between the signal wire and battery voltage, or between the signal wire and another sensor's wiring
- Open circuit in the 5-volt supply wire or the sensor return (ground) wire
- Faulty ECM, though this is rated as one of the less common causes
How to troubleshoot CAT Engine 2743: first checks
- Inspect the sensor connector for corrosion, bent pins, or a connector that is not fully seated. Clean and reseat as needed.
- Check the wiring harness between the sensor and the ECM for chafe points, pinches, or corrosion, particularly anywhere the harness runs near moving parts or heat sources.
- With a meter, verify supply voltage at the sensor connector. The ECM should be supplying 5.0 volts DC (some variants specify 5 ± 0.2 volts DC) on the supply pin, with pin -63 as the supply and pin -6 as the common return on the ECM side.
- Check the signal wire for a short to battery voltage or to another sensor's signal or supply wire, since a short to +battery is the specific condition that sets this code.
- Confirm the correct sensor part number is installed. An incorrect sensor is listed as a possible cause.
- If wiring and connectors check out, test or swap the atmospheric pressure sensor itself before condemning the ECM.
How the code clears
No separate clearing step is listed beyond fixing the underlying wiring, connector, or sensor fault. Once the ECM reads a valid signal within the normal operating range (the sensor's working range is 4.7 to 111.5 kPa, or 0.7 to 16.1 psi, output as 1.7 to 4.8 VDC), the fault should stop logging on its own. Cycling the key so the ECM can complete its automatic calibration, which happens in the first five seconds after keyswitch ON as long as the engine is not cranked during that window, may help confirm the repair.
Affected models and serial ranges
2743 appears in our records across 10 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C10 | Serial range not listed in source records |
| C11 | Serial range not listed in source records |
| C12 | Serial range not listed in source records |
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C16 | Serial range not listed in source records |
| C175 | Serial range not listed in source records |
| C18 | Serial range not listed in source records |
| C27 | Serial range not listed in source records |
| C32 | Serial range not listed in source records |
Frequently asked questions
What does CAT code 2743 mean?
It means the ECM is reading atmospheric pressure sensor signal voltage above 4.8 volts DC, which it interprets as a short to battery voltage. The ECM logs the fault and switches to a backup sensor or default pressure value.
Will code 2743 shut down my engine?
No. This code triggers a power derate rather than a shutdown. Depending on conditions, the derate can be as high as 24 percent plus a 20 percent filter derate, for a combined 44 percent power loss, so the engine keeps running but underpowered.
Can I keep operating with this code active?
You can operate, but expect reduced power, especially noticeable at higher elevations where the engine normally derates power anyway above roughly 7500 to 17000 ft (below 76.5 kPa / 11 psi atmospheric pressure). It's best to get it diagnosed within the shift.
What's the most common cause of this fault?
Wiring and connector problems are the most frequently cited causes: corrosion, damaged pins, pinched harness sections, or an open or short circuit. The sensor itself or the ECM are less common culprits but should be checked if wiring is confirmed good.
How do I test the atmospheric pressure sensor circuit?
Check for 5.0 volts DC supply at the sensor connector (pin -63 supply, pin -6 return on the ECM side), inspect the signal wire for shorts to battery voltage, and confirm the sensor's output falls between 1.7 and 4.8 VDC across its working range of 4.7 to 111.5 kPa.
Does this code affect all CAT engines the same way?
The affected models include C10, C11, C12, C13, C15, C16, C175, C18, C27, and C32. The exact timing thresholds and default substitute values vary slightly by ECM software version, but the underlying cause, a signal voltage above 4.8 volts DC, is the same across all of them.
Is the ECM likely to be the problem?
Rarely. A faulty ECM is listed as a possible cause in every version of this diagnostic, but it is generally the last thing to check after wiring, connectors, and the sensor itself have been ruled out.