CAT Engine 27384 Fault Code: Turbocharger #1 Compressor Inlet Pressure Sensor : Voltage Below Normal
Also called Engine Turbocharger 1 Compressor Inlet Pressure : Voltage Below Normal, Turbocharger #1 Compressor Inlet Pressure Sensor - Voltage Below Normal, Turbocharger #1 Compressor Inlet Pressure Sensor:Voltage Below Normal
Turbocharger #1 Compressor Inlet Pressure Sensor : Voltage Below Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 27384 (SPN 2738 / FMI 4) means the ECM sees the Turbocharger #1 compressor inlet pressure sensor signal voltage below the normal acceptable range, usually pointing to the absence of pull-up voltage on the signal circuit. This affects C13, C15, C175, C18, C27, and C32 engines. The ECM logs the code and substitutes a default value for the sensor reading while the fault is active.
Medium severity. This is a sensor circuit fault, not an immediate mechanical failure. The engine will keep running on a default substitute value, but boost control and turbo-related diagnostics lose accuracy until the sensor circuit is repaired.
What does CAT Engine error code 27384 mean?
Fault code 27384 is CAT's designation for SPN 2738 / FMI 4, which flags a low-voltage condition on the Turbocharger #1 compressor inlet pressure sensor's signal circuit. This sensor tells the ECM the pressure of the air entering the turbocharger's compressor side, information the ECM uses as part of overall boost and air management calculations.
The ECM continuously applies a pull-up voltage on the signal wire so it can tell if the circuit is open or shorted. When that pull-up voltage disappears from the signal circuit, the ECM reads this as a short circuit condition and sets the code with FMI 4 (voltage below normal). When the code is active, the ECM logs it and substitutes a default value for the sensor's reading so the engine can keep operating, though boost-related calculations lose their real-time accuracy.
The sensor wiring uses three terminals: supply voltage on terminal 1, sensor return on terminal 2, and sensor signal on terminal 3. The ECM has built-in short circuit protection for its internal power supply, so a short to battery voltage will not damage the ECM itself.
What triggers a CAT Engine 27384 code?
The ECM detects signal voltage on the Turbocharger #1 compressor inlet pressure sensor circuit that is not in the acceptable range, specifically an absence of pull-up voltage on the signal circuit, which the ECM interprets as a short circuit condition.
Common causes of 27384
- Intermittent problem in the sensor circuit or connections
- Damaged connectors or wiring between the sensor and the ECM
- A problem within the wiring harness itself
- A faulty pressure sensor
- A faulty ECM (less common, checked only after wiring and sensor are cleared)
How to troubleshoot CAT Engine 27384: first checks
- Inspect the sensor connector at the Turbocharger #1 compressor inlet pressure sensor for corrosion, moisture, bent pins, or a loose fit.
- Check terminal 1 (supply voltage), terminal 2 (sensor return), and terminal 3 (signal) for damaged, pinched, or chafed wiring along the full harness run to the ECM.
- Wiggle-test the harness and connectors while watching for the fault to change state, since several listed causes are intermittent in nature.
- Confirm the wiring harness itself has no internal breaks or shorts to ground, separate from the connector at the sensor.
- If wiring and connectors check out, replace the pressure sensor and recheck for the fault before suspecting the ECM.
How the code clears
No separate clearing step is listed beyond repairing or replacing the faulty component. Once the wiring, connector, or sensor issue is corrected and the ECM sees a normal signal voltage on the circuit, the active fault should clear on its own. No reset procedure is listed for this code.
Affected models and serial ranges
27384 appears in our records across 6 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C13 | Serial range not listed in source records |
| C15 | 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 fault code 27384 mean?
It means the ECM detected voltage below the normal acceptable range on the signal circuit of the Turbocharger #1 compressor inlet pressure sensor, most often because the pull-up voltage the ECM applies to that circuit is missing, which reads as a short circuit.
Can I keep running the engine with code 27384 active?
The engine will typically keep running because the ECM substitutes a default value for the affected sensor reading. However, boost and air management calculations lose accuracy, so the issue should be diagnosed and repaired promptly rather than ignored.
What is SPN 2738 FMI 4 on a CAT engine?
SPN 2738 identifies the Turbocharger #1 compressor inlet pressure sensor, and FMI 4 means the ECM sees the signal voltage below the normal range. Together they correspond to CAT fault code 27384.
Which CAT engines can show fault code 27384?
This code applies to C13, C15, C175, C18, C27, and C32 engine models.
What usually causes this fault: the sensor or the wiring?
Both are common causes. Damaged connectors, chafed or pinched wiring, and general harness problems are frequently the culprit, but a faulty sensor is also a listed cause. Intermittent connection issues are common enough that a thorough wiggle-test is worth doing before replacing parts.
Does fixing the wiring clear the fault code automatically?
Once the underlying wiring, connector, or sensor problem is corrected and the ECM sees a normal signal voltage, the active fault should clear on its own. There is no separate reset procedure listed for this code.
Is fault code 27384 an emergency?
No. It is a sensor circuit fault rather than a mechanical failure, so it does not require an immediate shutdown. It should still be diagnosed within the shift since it affects boost-related sensor accuracy.