Case IH 3843 – ENGINE ECU: Turbine upstream temperature sensor: SRC low for turbine upstream temperature sensor

This code indicates a Signal Range Check (SRC) Low for the exhaust gas temperature (EGT) sensor located upstream of the turbine. The Engine Control Unit (ECU) is receiving a voltage signal from this sensor that falls below the minimum acceptable physical limit, typically pointing to a short circuit to ground in the sensor's wiring, a damaged connector, or an internally shorted/failed temperature sensor.

• Farmall
• skid steer
• Farmall 65C
• Farmall 115U
• Maxxum 110
• Maxxum 115
• Steiger series
• Quadtrac series
• SR175
• SV series

1. 1

   Visual Inspection: Inspect the wiring harness leading to the turbine upstream temperature sensor for melted insulation, chafing against hot exhaust components, or pinched wires that could cause a short to ground.

2. 2

   Connector Check: Disconnect the sensor and inspect the pins for corrosion, moisture, or damage.

3. 3

   Voltage/Circuit Check: With the sensor disconnected and the key ON, check the reference voltage coming from the ECU to the sensor connector. If the voltage is pulled down to 0V on the signal wire, there is a short to ground in the harness.

4. 4

   Sensor Resistance Test: Measure the resistance across the sensor's terminals. An EGT sensor reading near 0 ohms indicates an internal short, confirming the sensor is defective and needs replacement.

5. 5

   Plausibility Check: Using a diagnostic scan tool, check the live data for the turbine upstream temperature when the engine is completely cold. It should match the ambient air and coolant temperatures; an extreme value indicates the sensor has failed.

1. 1

   Cool Down

   Ensure the engine and exhaust system have completely cooled down to avoid severe burn risks.

2. 2

   Locate the Sensor

   Locate the turbine upstream temperature sensor threaded into the exhaust manifold or the exhaust piping immediately before the turbocharger inlet.

3. 3

   Disconnect Wiring

   Unplug the electrical connector for the sensor.

4. 4

   Remove the Sensor

   Spray penetrating oil on the sensor threads and allow it to soak. Carefully remove the sensor using a specialized sensor socket or a line wrench to avoid stripping the hex head.

5. 5

   Prepare the New Sensor

   If the new sensor does not come with pre-applied thread lubricant, apply a small amount of high-temperature anti-seize compound to the threads, avoiding the sensor probe itself.

6. 6

   Install

   Thread the new sensor into the exhaust manifold by hand to prevent cross-threading, then tighten to the OEM torque specification.

7. 7

   Reconnect

   Plug in the electrical connector and ensure the wiring pigtail is secured and routed safely away from the hot exhaust housing.

8. 8

   Clear Codes

   Use a diagnostic tool to clear the 3843 fault code from the Engine ECU. Start the engine and monitor the live EGT data to verify the sensor is reading correctly and the code does not return.