CLAAS 777Bh – Eng A15: Fresh Air Intake Temp Voltage High

The engine control module has detected that the signal voltage from the fresh air intake temperature sensor (B222) is higher than the expected maximum threshold. This typically indicates an open circuit or a failed sensor, causing the signal voltage to pull up to its 5-volt reference level. When active, the engine module may disregard the faulty reading and substitute a default intake air temperature of 50°C, which can cause suboptimal engine performance, increased fuel consumption, and hard starting in cold conditions.

• Axion 800
• Axion 810
• Axion 850
• Arion 500 Series
• Arion 600 Series

1. 1

   Visually inspect the wiring harness and connector for the fresh air intake temperature sensor (B222) for damage, corrosion, dirt, or loose connections.

2. 2

   Check for an open circuit in the signal or ground wires leading to the sensor.

3. 3

   Perform a voltage test at the harness-side connector with the ignition on (engine off) to verify the presence of a 5-volt reference signal and a good ground.

4. 4

   Measure the electrical resistance across the sensor terminals; an infinite reading indicates an internally open and faulty sensor.

1. 1

   Disconnect the Battery

   Before beginning repairs, disconnect the vehicle's battery to prevent electrical damage.

2. 2

   Locate and Access the Sensor

   Locate the fresh air intake temperature sensor (B222). Its precise location can vary, but it is typically mounted in the air intake path, often in the air filter housing or the intake manifold.

3. 3

   Perform Diagnostic Checks

   Follow the diagnostic checks listed in the section above to confirm whether the fault lies with the sensor, its connector, or the wiring harness.

4. 4

   Replace the Sensor (if faulty)

   If the sensor is identified as the cause, remove it from its mounting. This usually involves unclipping it or removing a single retaining bolt. Install the new sensor, ensuring a secure fit.

5. 5

   Repair Wiring (if faulty)

   If the diagnostic checks point to a wiring or connector issue, repair or replace the damaged section of the harness or the connector itself.

6. 6

   Reconnect and Clear Codes

   Once the repair is complete, reconnect the sensor and the battery. Use a diagnostic tool to clear the 777Bh fault code from the Engine Module (A15).

7. 7

   Verify the Repair

   Start the engine and allow it to run through several warm-up cycles. Re-check for any pending or active fault codes to ensure the repair has been successful.