CAT Engine 2744 Fault Code: Atmospheric Pressure short to ground
Also called Atmos Press Signal Shorted to Ground, Atmosperic Pressure Sensor : Voltage Below Normal, Atmospheric Pressure Short to Ground, Atmospheric Pressure Sensor : Voltage Below Normal, Atmospheric Pressure Sensor Voltage Below Normal, Atmospheric Pressure Sensor voltage below normal, Atmospheric Pressure Sensor: Voltage Below Normal, Atmospheric Pressure Sensor:Voltage Below Normal, Atmospheric Pressure Short to Ground, Atmospheric Pressure Signal Shorted to Ground, Barometric Pressure : Voltage Below Normal
Atmospheric Pressure short to ground · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 2744 (SPN 274, FMI 4) means the ECM sees the atmospheric pressure sensor signal voltage below normal, often a short to ground. The ECM substitutes the right turbo inlet pressure sensor or a default value, and the engine can lose power until the fault is fixed.
Medium severity. The engine keeps running but goes into a power derate. It is not an immediate shutdown risk, but ignoring it costs power and can mask real altitude compensation, so it should be diagnosed the same shift.
What does CAT Engine error code 2744 mean?
Code 2744 is set when the CAT ECM detects that the atmospheric pressure sensor's signal voltage is below the normal operating range, which the ECM interprets as a short to ground on that circuit.
The atmospheric pressure sensor tells the ECM what the outside air pressure is so the engine can correctly adjust fueling and power output for altitude. Without a good signal, the ECM cannot tell if the engine is at sea level or high elevation, so it falls back on a substitute reading or a fixed default value.
When this happens, the ECM first tries to use the right turbo compressor inlet pressure sensor in place of the atmospheric pressure sensor. If that signal is also out of range, the engine is derated 24 percent for altitude compensation plus 20 percent for filter restriction, for a combined derate of 44 percent. In other listed versions of this fault, the ECM instead flags atmospheric pressure as invalid and substitutes a default value of 100 kPa (14.5 psi) or 45 kPa (6.5 psi), depending on the specific ECM software, and the engine may run with low power.
What triggers a CAT Engine 2744 code?
The ECM reads atmospheric pressure signal voltage below 1.7 volts (a short to ground) in one listed version. Another version sets the code when the signal voltage is below 1.72 VDC for one second with the ECM powered for at least three seconds. A related version notes the ECM detects signal voltage below normal for thirty seconds with the ECM powered for two seconds. The sensor itself is supplied 5.0 volts DC (or 5 ± 0.2 VDC in one version) from the ECM, with a normal sensor output range of 1.7 to 4.8 VDC corresponding to a pressure range of 4.7 to 111.5 kPa (0.7 to 16.1 psi).
Common causes of 2744
- Leaks in the sensor's air reference system
- Atmospheric pressure sensor has failed and needs replacement
- Damaged, corroded, or loose connector or wiring, including pinch points or abrasion in the harness
- A problem elsewhere in the harness between the ECM and the sensor
- Incorrect sensor installed for the application
- Open or short circuit in the signal wire, including a short between the signal wire and sensor common, or a short between the 5-volt supply and the signal wire
- Open circuit in the 5-volt supply wire
- Faulty or intermittent connection in the harness, including connectors, pins, and sockets not fully seated
- Defective ECM
How to troubleshoot CAT Engine 2744: first checks
- Turn the key off, then back on and let the ECM complete its power-up calibration before cranking. If the engine is cranked before the calibration window ends, the ECM uses the prior stored calibration instead of a fresh one.
- Inspect the atmospheric pressure sensor connector and the ECM connector for corrosion, bent pins, or a connector that is not fully seated.
- Check the wiring harness between the ECM and the sensor for chafe points, pinches, or abrasion damage, especially anywhere it crosses moving parts or sharp edges.
- With a meter, verify the sensor is getting its supply voltage (around 5.0 volts DC, or 5 ± 0.2 VDC depending on the ECM version) at the sensor connector.
- Check the signal wire for a short to ground or a short to the 5-volt supply wire, and check the sensor common/return wire for continuity back to the ECM.
- If wiring and connectors check good, swap in a known-good atmospheric pressure sensor and recheck for the fault.
- If the fault persists with a good sensor and good wiring, suspect the ECM.
How the code clears
No separate clearing step is listed beyond fixing the underlying wiring, connector, or sensor problem. Once the ECM sees a valid atmospheric pressure signal within the normal voltage range, the code should stop being active; a scan tool can be used to confirm the code has cleared and to check whether the derate has lifted.
Affected models and serial ranges
2744 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 2744 mean?
It means the engine ECM is reading a signal voltage from the atmospheric pressure sensor that is below normal, which the ECM treats as a short to ground on that circuit. The ECM cannot get a reliable atmospheric pressure reading, so it substitutes another sensor or a default value.
Will code 2744 cause a power loss?
Yes, it can. If the ECM also cannot use the right turbo compressor inlet pressure sensor as a backup, full load engine power is derated 24 percent for altitude compensation plus 20 percent for filter restriction, a total derate of 44 percent. In other cases the engine may simply run with low power while the ECM uses a default pressure value.
Is it safe to keep driving or working with this code active?
The engine will typically keep running, but expect reduced power, especially at higher engine loads or altitude. It's best to get the sensor and wiring checked as soon as practical rather than running long-term on a substituted or default pressure value.
What usually causes this fault?
The most common causes are a failed atmospheric pressure sensor, damaged or corroded wiring or connectors, a short to ground on the signal wire, or an open in the 5-volt supply wire. Less commonly, the wrong sensor was installed, or the ECM itself is faulty.
How is the atmospheric pressure sensor wired?
The sensor gets a regulated supply voltage from the ECM (around 5.0 volts DC, specified in some ECM versions as 5 ± 0.2 VDC), a sensor return/common line, and a signal wire that carries the variable voltage output, normally between 1.7 and 4.8 VDC, back to the ECM.
Can I just replace the sensor to fix code 2744?
Sometimes, but check the wiring and connectors first. Since the code covers a short-to-ground condition and low signal voltage, a damaged harness or corroded connector is just as likely a cause as a bad sensor itself. Replacing the sensor without checking wiring can mean the fault comes right back.
Does this code affect altitude compensation?
Yes. The atmospheric pressure sensor signal is what allows the ECM to limit engine power appropriately at high elevation. Rated power is normally available until atmospheric pressure drops below 76.5 kPa (11 psi), after which power is reduced at a rate of 1 percent per kPa (.15 psi) of pressure drop, up to a maximum derate of 24 percent, roughly in the 7500 ft to 17000 ft range. With this code active, that compensation logic is running on a substitute or default value instead of a real reading.