Case IH F-4363-01 - ECU – Engine Control Unit (ECU): Downstream SCR catalyst temperature sensor voltage is lower than expected

The Engine Control Unit has detected a voltage signal from the downstream exhaust gas temperature sensor that is below the normal operating range (typically indicating a short to ground, an open circuit, or an internal sensor failure). When this fault occurs, the ECU will often freeze the temperature reading at a default replacement value or its last valid value, which can trigger a derate or "limp mode".

• MAGNUM AFS Connect
• Maxxum (115-150)
• Puma (140-240)
• Magnum
• Optum
• Steiger
• Farmall series
• Patriot series (e.g., 4430)
• WD series (WD1204 - WD2504)

1. 1

   Verify the fault is active using the AFS Pro display or the Electronic Service Tool (EST).

2. 2

   Turn the ignition OFF and disconnect the downstream SCR temperature sensor electrical connector.

3. 3

   Inspect both the sensor and harness connectors for bent, spread, pushed-back, or corroded pins. Moisture intrusion is a common cause of voltage drops.

4. 4

   Perform a continuity check on the vehicle engine harness between the sensor connector and the ECU connector to rule out a short to ground or an open wire.

5. 5

   Measure the resistance across the pins of the SCR temperature sensor using a multimeter. If the resistance is out of range for the current ambient temperature, the sensor has failed internally and must be replaced.

1. 1

   Turn the ignition switch to the OFF position and allow the exhaust system to cool completely to avoid severe burns.

2. 2

   Locate the downstream SCR catalyst temperature sensor.

   It is threaded into the exhaust pipe immediately after the SCR muffler/catalyst.

3. 3

   Disconnect the electrical harness connector from the sensor.

4. 4

   Using a wrench (typically 17mm), carefully unscrew and remove the faulty temperature sensor from the exhaust system.

5. 5

   Install the new exhaust gas temperature sensor into the exhaust pipe.

   (If the new sensor does not have pre-applied anti-seize on the threads, apply a small amount of high-temp sensor-safe anti-seize, being careful not to get any on the probe itself). Torque to OEM specifications.

6. 6

   Reconnect the electrical harness connector until it clicks securely.

7. 7

   Turn the ignition ON and use the Electronic Service Tool (EST) to clear the fault codes, or run the machine through a healing procedure/key cycles to verify the code does not return and the system exits limp mode.