Case IH 3986 – Engine Control Unit (ECU): Turbine Upstream Pressure Sensor: SRC Low

The Engine Control Unit (ECU) detects that the voltage signal from the Turbine Upstream Pressure Sensor has dropped below the minimum acceptable threshold (typically near 0V). This indicates a physical short to ground in the sensor's wiring harness, a completely failed sensor, or an excessively low physical pressure reading.

• 5140
• 6140
• 7140
• 7240
• 8240
• 9240
• Magnum
• Steiger
• Puma
• Maxxum
• 1021G
• 1121G

1. 1

   Perform a plausibility check (Key On, Engine Off) using a diagnostic tool to compare the Turbine Upstream Pressure Sensor reading to the Ambient Air Pressure Sensor reading (should be within 7.5 kPa).

2. 2

   Inspect the 3-pin connector and wiring harness for a 5V reference signal, a good ground from the ECU, and any chafed wires shorting the signal wire to chassis ground.

3. 3

   Disconnect the metal tube connecting the sensor to the exhaust manifold and check for heavy soot or carbon blockages that can skew pressure readings.

1. 1

   Preparation

   Turn off the engine, remove the key, and allow the exhaust system and turbocharger to cool completely to avoid severe burns.

2. 2

   Locate the Sensor

   Find the Turbine Upstream Pressure Sensor, which is typically mounted on a bracket near the turbocharger and connected to the exhaust manifold via a metal line.

3. 3

   Disconnect

   Unplug the electrical harness connector from the sensor.

4. 4

   Removal

   Using the appropriate wrench, carefully unscrew the sensor from the exhaust pressure tube. Tip: Use penetrating oil on the threads to prevent twisting or breaking the metal tube.

5. 5

   Clean the Tube

   Inspect the metal tube. If it is clogged with soot, remove the tube entirely and clean it out with a wire brush and compressed air. If it is damaged, it must be replaced.

6. 6

   Installation

   Thread the new exhaust pressure sensor onto the tube and tighten to OEM torque specifications.

7. 7

   Reconnect

   Plug the electrical connector back into the sensor.

8. 8

   Clear Codes

   Turn the key to the ON position and use the CNH Electronic Service Tool (EST) or a compatible OBD scanner to clear the inactive fault codes.

9. 9

   Test

   Start the engine and monitor the exhaust pressure parameters under load to ensure the sensor is reading correctly and the code does not return.