CAT Engine 1103 Fault Code: Engine Coolant Temperature open/short to +batt

What does CAT Engine error code 1103 mean?

Code 1103 (SPN 110 / FMI 3) on CAT C10 through C32 series engines means the ECM is reading an engine coolant temperature sensor signal voltage that is too high, which it interprets as an open circuit or short to battery voltage rather than a real temperature reading.

The coolant temperature sensor is a simple two-terminal device that lets the ECM know how warm the engine is so it can manage cold mode operation, idle strategy, injection timing, and fan control. When the ECM cannot trust this signal, it substitutes a default value (some ECM versions default to 90°C (194°F), one version defaults to -40°C (-40°F)) instead of the real reading.

Because the ECM assumes a default temperature, the engine will not properly enter cold mode strategy, and the operator may notice misfires, poor stability, poor cold running, white smoke, reduced engine speed, or low power depending on actual conditions and which default value is applied.

What triggers a CAT Engine 1103 code?

Multiple ECM software versions log this code slightly differently. Common set conditions include: signal voltage equal to or greater than 4.8 VDC for 0.24 seconds with the ECM powered up for 2 seconds; signal voltage above 4.8 VDC for 1 second with the ECM powered for at least 3 seconds (and no active 262-03 or 262-04 codes); signal voltage above 4.95 VDC for more than 8 seconds with the ECM powered for at least 2 seconds (and no active 168-X codes); and on one version, the code only logs if the engine has run for more than 7 minutes, with the cooling fan activated once the code has been active for more than 8 seconds.

Common causes of 1103

• Damaged, corroded, or loose connectors and wiring at the coolant temperature sensor or ECM connector
• Open or short circuit in the signal wire, including a short to battery voltage or a short between the sensor common and signal wire
• Faulty or failed engine coolant temperature sensor that needs replacement
• Problem in the engine harness, including pinch points or abrasion damage
• 5-volt supply wire (where applicable) with an open circuit or shorted to the signal wire
• Intermittent connection issues, such as pins or sockets not fully seated
• Defective ECM (less common, checked only after wiring and sensor are confirmed good)

How to troubleshoot CAT Engine 1103: first checks

1. 1Inspect the coolant temperature sensor connector and ECM connector (J1/P1 or J2/P2) for corrosion, bent pins, or a connector that is not fully seated
2. 2Visually trace the harness between the sensor and the ECM looking for chafe points, pinches, or heat damage that could cause a short to battery or ground
3. 3Check the sensor signal wire (terminal 1) and common/return wire (terminal 2) for continuity and confirm there is no short to the battery or to the 5-volt supply circuit shared with other analog sensors
4. 4With the key on and engine off, check sensor signal voltage against ECM specification to see if it reads abnormally high, which points to an open or short-to-battery condition rather than a bad sensor alone
5. 5Confirm no related codes are active at the same time (for example 262-03, 262-04, or 168-X codes), since some ECM logic will not log 1103 if those are already active
6. 6If wiring and connectors check good, test or swap the coolant temperature sensor itself before condemning the ECM

How the code clears

No separate clearing step is listed beyond repairing the wiring, connector, or sensor fault that triggered the code. Once the signal voltage returns to a normal range, the ECM should stop flagging coolant temperature as invalid and resume using live sensor data. Use a diagnostic scan tool to confirm the code has gone inactive after the repair and to verify the ECM is once again reading real coolant temperature instead of a default value.

Affected models and serial ranges

1103 appears in our records across 10 CAT Engine models. Match your machine by model and serial number.