Case IH 3837 – Engine Control Unit (ECU): OxiCat downstream temperature sensor : SRC low

The control module is receiving a voltage signal from the exhaust gas temperature sensor (located downstream of the Diesel Oxidation Catalyst / OxiCat) that is below the minimum acceptable threshold. This typically indicates a short circuit to ground in the sensor's wiring, a failed sensor, or an unplugged connector.

• Case IH, New Holland, and Steyr agricultural and construction equipment equipped with FPT Tier 4a, Tier 4b, Stage IV, or Stage V engines

1. 1

   Inspect the wiring harness leading from the ECU to the DOC downstream temperature sensor for chafed wires, melted insulation from exhaust heat, or pinched lines.

2. 2

   Disconnect the sensor and inspect the connector pins for water intrusion, corrosion, or bent pins.

3. 3

   With the key ON (engine off), use a multimeter to check the sensor supply voltage from the ECU harness. Check the signal wire for continuity to ground to confirm the short to ground condition.

4. 4

   Measure the resistance across the sensor pins at room temperature. If it reads as a dead short (0 ohms) or completely open (infinite ohms), the sensor has failed internally.

1. 1

   Cool Down

   Ensure the machine has been turned off and the exhaust system has completely cooled, as the DOC operates at extremely high temperatures.

2. 2

   Locate the Sensor

   Locate the Diesel Oxidation Catalyst (DOC) in the exhaust stream. Find the temperature sensor threaded into the exhaust pipe downstream (after) the DOC housing.

3. 3

   Disconnect

   Unplug the electrical connector for the sensor.

4. 4

   Remove Sensor

   Using an appropriate sensor socket or wrench, carefully unscrew the temperature sensor from the exhaust pipe. (Penetrating oil may be required if the sensor is seized).

5. 5

   Install 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-coated). Thread it in by hand to prevent cross-threading.

6. 6

   Torque

   Tighten the sensor to the OEM specification (typically around 35 ft-lbs / 47 Nm).

7. 7

   Reconnect

   Plug the electrical connector back into the engine harness and secure any loose wiring with zip ties away from heat sources.

8. 8

   Clear Codes

   Connect the CNH EASy diagnostic tool (or equivalent scanner) to clear the inactive fault code 3837 from the ECU memory.