CAT Engine 1003 Fault Code: Engine Oil Pressure open/short to +batt
Also called Engine Oil Pressure : Voltage Above Normal, Engine Oil Pressure Open/ Short to +Batt, Engine Oil Pressure Open/Short to +Batt, Engine Oil Pressure Sensor - Voltage Above Normal, Engine Oil Pressure Sensor : Voltage Above Normal, Engine Oil Pressure Sensor : Voltage Below Normal, Engine Oil Pressure Sensor Voltage Above Normal, Engine Oil Pressure Sensor Voltgae Above Normal, Engine Oil Pressure Sensor voltage above normal, Engine Oil Pressure Sensor: Voltage Above Normal, Engine Oil Pressure Sensor:Voltage Above Normal, Oil Pressure Signal Open/Short to Batt+
Engine Oil Pressure open/short to +batt · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 1003 (SPN 100 / FMI 3) means the ECM sees engine oil pressure sensor signal voltage above normal, typically above 4.8 volts DC or 4.95 volts DC depending on the ECM software, for more than 8 seconds. The ECM logs the code, sets oil pressure data to a default value of 600 kPa (87 psi), and turns on the warning lamp. Engine operation is usually not restricted, but actual oil pressure is unknown while this code is active.
Medium severity. The ECM does not restrict engine operation and continues running with a default oil pressure value, but that default masks the real oil pressure. If actual oil pressure is low, low or no-oil-pressure damage can occur without the operator knowing. Treat this as a diagnose-soon issue, not a stop-now emergency, unless other symptoms of low oil pressure appear.
What does CAT Engine error code 1003 mean?
CAT fault code 1003 fires when the ECM reads the engine oil pressure sensor's signal wire at a voltage above the normal operating range, which points to an open circuit or a short to a power source (battery voltage) rather than an actual oil pressure reading.
The engine oil pressure sensor sends a variable DC voltage signal to the ECM that normally runs between 0.2 and 4.42 volts DC, corresponding to a sensor pressure range of 0 to 690 kPa (0 to 100 psig). The ECM compares this signal against a stored map of expected oil pressure versus engine rpm.
When the signal voltage climbs above normal, the ECM cannot trust the reading, so it logs the code, turns on the oil warning lamp, and substitutes a default oil pressure value of 600 kPa (87 psi) on the display. This means the gauge or scan tool reading no longer reflects the engine's actual oil pressure until the fault is fixed.
What triggers a CAT Engine 1003 code?
The ECM detects sensor signal voltage above normal for 8 seconds, with the exact threshold cited as either 4.8 volts DC or 4.95 volts DC depending on the software version. The ECM must have been powered for at least 2 seconds before the code can set. On at least one software version, the code also requires the engine to not be running, or the engine coolant temperature to be greater than 38°C (100°F), and requires that no active 262 or 168 codes be present at the same time.
Common causes of 1003
- Damaged, corroded, or abraded connectors or wiring in the harness between the ECM and the oil pressure sensor
- Open circuit or excessive resistance in the sensor signal wire or the sensor common (return) wire
- Short circuit between the sensor harness connector and the ECM, or a short to another power source such as battery voltage
- Faulty or defective engine oil pressure sensor
- Sensor supply voltage out of the normal range (the sensor is supplied with 5.0 volts DC, routed through ECM connector pins, commonly labeled J1/P1 pin -63 for supply, pin -6 for return, and pin -10 for signal on some ECM families)
- Intermittent wiring fault that only shows up under vibration or temperature swings
- Faulty ECM
How to troubleshoot CAT Engine 1003: first checks
- Check the wiring harness and connectors between the ECM and the oil pressure sensor for corrosion, abrasion, pinched wires, or loose pins
- Verify the sensor supply voltage is present and correct at the sensor connector (nominally 5.0 volts DC)
- Inspect the sensor connector terminals: supply on terminal 1, sensor return on terminal 2, and signal on terminal 3 for most pressure sensors on this ECM family
- Check the actual engine oil level and look for any signs of an existing oil leak so you are not chasing a wiring fault while ignoring a real oil issue
- Use a scan tool to confirm the active code and check for other active codes (such as 262 or 168 type codes) that may need to be resolved first
- Test the sensor signal wire for an open circuit or a short to a power source between the ECM and the sensor connector
- If wiring and supply voltage check out, test or swap the oil pressure sensor to confirm whether it is producing a valid signal
How the code clears
No separate clearing step is listed beyond repairing the underlying wiring, connector, sensor, or ECM fault. Once the signal voltage returns to a normal range and stays there, the ECM will stop logging the active code. Use a scan tool to verify the code goes inactive and, if needed, clear the logged/stored code after the repair is confirmed.
Affected models and serial ranges
1003 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
Does CAT code 1003 mean my engine is low on oil?
Not necessarily. Code 1003 means the ECM is seeing an electrical signal problem, voltage above normal, from the oil pressure sensor circuit, not a confirmed low oil pressure condition. However, since the ECM switches to a default oil pressure value of 600 kPa (87 psi) while this code is active, you should still check your actual oil level and look for leaks, because you cannot trust the gauge reading until the fault is fixed.
Is it safe to keep running the engine with code 1003 active?
The ECM does not restrict engine operation for this code, and it logs the fault while displaying a default oil pressure. That said, running with an unreliable oil pressure reading carries risk if there is an underlying real oil pressure problem. It is best treated as a medium priority: diagnose and repair it within the shift rather than ignoring it.
What voltage triggers CAT fault code 1003?
Different ECM software versions cite slightly different thresholds: signal voltage above 4.8 volts DC or above 4.95 volts DC, sustained for more than 8 seconds, with the ECM powered for at least 2 seconds before the code can set.
What is the normal operating voltage and pressure range for the oil pressure sensor on this system?
The sensor produces a signal between 0.2 and 4.42 volts DC corresponding to an oil pressure range of 0 to 690 kPa (0 to 100 psig). It is supplied with 5.0 volts DC from the ECM.
Can a bad connector alone cause code 1003?
Yes. Damaged, corroded, or abraded connectors and wiring are listed as leading causes, along with open circuits, excessive resistance, or shorts to a power source in the sensor signal or return wiring.
Will code 1003 clear itself after I fix the wiring?
No separate clearing procedure is listed. Once the sensor signal voltage returns to and stays within the normal range, the ECM stops setting the code as active. You may still need to clear the stored/logged code with a scan tool after confirming the repair.
Are there conditions that need to be false before code 1003 can become active?
On one documented version, the code cannot become active if there are active 262 codes or active 168 codes at the same time. It may also require the engine to not be running, or coolant temperature above 38°C (100°F), depending on the software version.