CLAAS 7721h – ENG A15: Turbocharger Speed Sensor Malfunction

The engine control module detects that the intensity of the turbocharger speed sensor signal is too high and outside of its expected range. The engine will typically continue to run but will disregard the faulty information from the sensor. This loss of accurate turbocharger speed monitoring can lead to the engine entering a protective limp mode, resulting in sluggish acceleration, rough idle, surging, or excessive exhaust smoke.

• Axion
• Arion
• Axion 810
• Arion 510

1. 1

   Perform a visual inspection of the turbocharger speed sensor and wiring harness for damaged, frayed, or melted insulation due to hot exhaust components.

2. 2

   Check for loose or corroded electrical connectors, physical damage to the sensor, and accumulation of oil, soot, or debris.

3. 3

   Use a diagnostic scanner to check for any other active or stored fault codes, particularly those related to boost pressure.

4. 4

   Perform a continuity check on the wiring harness between the sensor and engine module to identify open circuits.

5. 5

   Test for short circuits between the sensor wires and to the chassis ground.

6. 6

   Verify the correct voltage supply (typically 5 volts) and a proper ground connection at the sensor's electrical connector with the ignition on.

7. 7

   Monitor the live data stream for the turbocharger speed using a diagnostic tool, observing for unresponsive or erratic RPM readings as engine speed changes.

1. 1

   Prepare machine

   Ensure the engine is turned off and has cooled down completely. Disconnect the vehicle's battery.

2. 2

   Disconnect sensor

   Locate the turbocharger speed sensor on the turbocharger housing and carefully disconnect the electrical connector.

3. 3

   Remove sensor

   Remove the single retaining bolt and carefully pull the sensor straight out of its bore in the turbo housing.

4. 4

   Clean mounting bore

   Clean the sensor mounting hole and ensure it is free from dirt and debris before installing the new sensor.

5. 5

   Install new sensor

   Insert the new turbocharger speed sensor into the housing and secure it with the retaining bolt. Do not overtighten.

6. 6

   Secure wiring

   Reconnect the electrical connector, ensuring it clicks into place. Secure the wiring harness away from any hot or moving parts using zip ties to prevent future damage.

7. 7

   Clear Fault Codes

   Reconnect the battery. Use a diagnostic tool to clear the 7721h fault code and any other related codes from the engine module's memory.

8. 8

   Test Drive

   Start the engine and perform a test drive, bringing the engine up to operating temperature and load to verify that the fault does not return.