How to Troubleshoot a Cummins Engine Temperature Sensor (Step-by-Step Guide)

How to Troubleshoot a Cummins Engine Temperature Sensor (Step-by-Step Guide)

The engine temperature sensor on a Cummins diesel engine is critical for keeping operating temperatures in a safe range. When the sensor or its wiring fails, the engine may enter a derate mode, lose power, or run inefficiently. Understanding how to troubleshoot and maintain this component can prevent downtime and costly repairs.

What the Sensor Controls

The Cummins temperature sensor affects several systems:

• Cooling fan operation
• Turbo boost control logic
• Fuel injection volume
• Exhaust aftertreatment temperatures (DPF & SCR systems)
• Idle speed regulation

Because the sensor ties into emissions and safety systems, sensors are calibrated with high accuracy.

Common Fault Codes Related to the Sensor

If the sensor malfunctions, the ECM may activate fault codes such as:

A scan tool or Cummins INSITE software is helpful for pinpointing the problem.

Troubleshooting Checklist

1. Check Coolant Level

Low coolant can cause incorrect temperature readings.
→ Refill and check for leaks.

2. Inspect Wiring Harness

Look for:

Cracked insulation

Broken connectors

Corrosion in terminals

3. Test Sensor Resistance

Compare ohm values versus Cummins temperature-resistance charts.
If reading does not match → Replace sensor.

4. Check ECM Inputs

If wiring and sensor are good, the ECM input circuit may be damaged.
Professional diagnosis is required in this case.

Replacement Tips

Always perform the replacement when the engine is cool.

Use thread sealant or factory-approved sealing washer.

After installation, run engine and verify temperature rises smoothly.

Clear fault codes using diagnostic tools.

How to Protect the Sensor from Future Damage

Maintain fresh coolant with correct chemical balance.

Avoid mixing coolant types (can cause corrosion).

Keep engine ground connections clean to prevent electrical issues.

Replace coolant hoses before they become brittle.

Why Use Genuine or OEM-Quality Sensors?

Low-quality substitutes may have incorrect resistance characteristics, causing:

• Poor fuel efficiency
• Overheating risks
• False warning codes
• Premature ECM failures

Investing in a high-quality Cummins-compatible sensor ensures accurate, stable engine control.