Case IH 3840 – ENGINE: Exhaust Gas Temperature 1 Sensor Signal Too High

The Engine Control Unit (ECU) is receiving a voltage signal from the Exhaust Gas Temperature (EGT) Sensor 1 that exceeds the maximum allowable threshold. This condition is almost always caused by an open circuit in the sensor wiring, a short to power (battery voltage), or an internal failure of the sensor itself causing infinite resistance.

• skid steer
• Skid Steer Loaders (SSL) & Compact Track Loaders (CTL)
• SR175
• Steiger series
• Farmall series (100C, 105A, 105C, 105U, 110A, 110C, 110U, 115A, 115C, 115U, 120U)
• Maxxum series (120, 125, 130, 140)
• Puma series (140)
• Combines (5130, 7130, 7240, 9230)

1. 1

   Inspect the EGT 1 sensor wiring harness for chafing, melting from exhaust heat, or damage that could cause an open circuit or short to voltage.

2. 2

   Disconnect the EGT sensor and inspect the connector pins for corrosion, moisture, or bent terminals.

3. 3

   Use a multimeter to measure the resistance across the EGT sensor's pins (an infinite resistance reading confirms the sensor has failed internally).

4. 4

   With the key ON and the sensor disconnected, check the harness side for the proper 5V reference signal and a good ground to ensure ECU communication.

1. 1

   Prep the Machine

   Turn off the engine, remove the key, and disconnect the battery to prevent electrical shorts. Allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Locate the EGT 1 sensor on the exhaust pipe, typically positioned downstream of the oxidation catalyst (Oxicat) or at the DPF intake.

3. 3

   Disconnect Wiring

   Unplug the electrical connector from the sensor harness.

4. 4

   Remove the Sensor

   Using a 17mm wrench, carefully unscrew the faulty EGT sensor. Note: If the sensor is seized due to exhaust heat cycles, apply penetrating oil and allow it to soak before applying force to avoid stripping the exhaust bung threads.

5. 5

   Install the New Sensor

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it does not come pre-applied). Thread it in by hand to prevent cross-threading, then tighten to the manufacturer's torque specification.

6. 6

   Reconnect

   Plug the electrical connector back into the engine harness until it clicks.

7. 7

   Clear Codes

   Reconnect the battery, turn the key ON, and use a diagnostic scan tool (EST) to clear the 3840 fault code. Start the engine and verify the code does not return.