New Holland ENG 3838 – Engine Control Unit (ECU): Oxidation catalyst upstream temperature shorted to high source

The Engine Control Unit (ECU) has detected that the voltage signal from the exhaust gas temperature sensor #1 (located upstream of the Diesel Oxidation Catalyst / DPF) is abnormally high (typically above 5.0V - 5.2V). This indicates a Signal Range Check (SRC) High failure, which is almost always caused by a short circuit to a high voltage source in the sensor itself, the wiring harness, or the ECU.

• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• Backhoe Loaders
• Tractors
• Combines
• CR9090
• CX8080
• CX8090

1. 1

   Connect the Electronic Service Tool (EST) to the diagnostic port to confirm ENG 3838 is currently active.

2. 2

   Inspect the wiring harness leading to the upstream DOC/DPF temperature sensor for melted insulation, chafing against the hot exhaust pipe, or pinched wires.

3. 3

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

4. 4

   With the sensor disconnected, turn the key ON and measure the voltage at the harness connector to ensure the ECU is sending the correct 5V reference voltage.

5. 5

   Test the sensor's internal resistance; an internal short will read out of specification.

6. 6

   Check the continuity of the signal wire back to the ECU pins to rule out a harness short.

1. 1

   Preparation

   Ensure the machine is parked on a level surface, the engine is turned off, and the exhaust system has completely cooled down to prevent severe burns. Disconnect the negative battery cable.

2. 2

   Locate the Sensor

   Locate the upstream exhaust gas temperature sensor. It is threaded into the exhaust pipe directly before the Diesel Oxidation Catalyst (DOC) and DPF assembly.

3. 3

   Disconnect

   Unplug the electrical connector for the sensor.

4. 4

   Removal

   Apply penetrating oil to the threads of the sensor and let it sit, as exhaust sensors frequently seize due to extreme heat cycles. Carefully use a line wrench or sensor socket to unthread the sensor from the exhaust pipe.

5. 5

   Installation

   Apply a small amount of anti-seize compound to the threads of the new sensor (if not pre-applied by the manufacturer). Thread the new sensor into the exhaust pipe and tighten to the OEM torque specification.

6. 6

   Reconnect

   Plug the sensor's electrical connector back into the engine wiring harness. Ensure it clicks securely into place and route the wire away from direct heat sources.

7. 7

   Clear Codes

   Reconnect the battery, turn the ignition on, and use the EST to clear the inactive ENG 3838 fault code. Run the engine and monitor the upstream temperature data to verify the repair.