Case IH 3985 – Engine Control Unit (ECU): Signal Range Check (SRC) High for the Turbine Upstream Pressure Sensor

The sensor measuring the exhaust gas pressure before the turbocharger (upstream) is sending a voltage signal to the control module that exceeds the maximum acceptable limit. This condition typically points to a short circuit to power (B+), an open ground circuit, a severely drifted/failed sensor, or a completely blocked signal tube.

• Puma
• Optum
• Magnum
• Steiger

1. 1

   Visually inspect the wiring harness and connector at the Turbine Upstream Pressure Sensor for physical damage, melted wires, corrosion, or loose pins.

2. 2

   Test the sensor's ground and signal circuits with a multimeter. Look for a short to battery voltage (B+) on the signal wire or an open circuit on the ground wire.

3. 3

   Inspect the exhaust gas pressure sensor signal tube (the metal tube connecting the exhaust manifold to the sensor) for severe soot or carbon blockages.

4. 4

   Connect the Case IH Electronic Service Tool (EST). With the key on and the engine off (KOEO), check the live data for the Turbine Upstream Pressure Sensor. It should read ambient atmospheric pressure. If it reads excessively high, the sensor is internally shorted or drifted and must be replaced.

1. 1

   Preparation

   Turn off the engine, remove the key, and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Locate the Sensor

   Locate the Turbine Upstream Pressure Sensor, which is typically mounted near the exhaust manifold and turbocharger area, connected via a metal signal tube.

3. 3

   Disconnect

   Unplug the electrical connector from the sensor.

4. 4

   Removal

   Carefully unscrew the sensor from the exhaust gas pressure signal tube. (Note: Use penetrating oil if the threads are seized due to high exhaust heat).

5. 5

   Clean the Tube

   Inspect the metal signal tube. If it is clogged with soot, remove the tube entirely and clean it out with a wire brush and solvent, or replace it if it is damaged.

6. 6

   Installation

   Thread the new Turbine Upstream Pressure Sensor into the signal tube and tighten it to the OEM specified torque.

7. 7

   Reconnect

   Plug the electrical connector back into the sensor, ensuring the locking tab clicks into place.

8. 8

   Clear Codes

   Reconnect the battery, turn the key on, and use the Case IH EST to clear the inactive 3985 fault code.

9. 9

   Verification

   Start the engine and monitor the exhaust pressure live data to verify the readings are within normal parameters and the fault code does not return.