John Deere 44 – ECU: Auxiliary Speed Input Error

The Engine Control Unit (ECU) has detected an erratic or missing signal from the auxiliary engine speed sensor while the primary engine speed signal remains valid. The auxiliary sensor serves as a backup source of engine speed information for functions like fuel injection timing and engine speed regulation. A mismatch or loss of this signal prompts the ECU to log code 44, which can lead to erratic engine performance such as loping or surging.

• 9300
• 9400
• 9500
• 9600
• 6650
• 6750
• 6850
• 6950
• 5R Series
• 6M Series
• 6R Series
• 7R Series
• 8R Series
• Machines equipped with certain Yanmar Diesel Engines

1. 1

   Verify battery connections are clean and tight, as poor connections can cause various electrical issues

2. 2

   Visually inspect the wiring harness leading to the engine speed sensors and the injection pump for signs of damage, chafing, rubbing, or corrosion

3. 3

   Disconnect, inspect, and reconnect the electrical connectors for the engine speed sensors and the ECU, checking for corrosion or bent pins

4. 4

   Perform a harness check by measuring resistance between specified pins in the engine harness with connectors disconnected (a reading of less than 5 ohms may indicate a harness fault)

5. 5

   Check for wear in the injection pump's cam bearings, which can cause the sensor wheel to rub against the sensor on models with a speed sensor located in the injection pump

1. 1

   Replace auxiliary speed sensor

   If wiring, connectors, and harness resistance checks are in good condition, replace the auxiliary engine speed sensor.

2. 2

   Inspect and replace injection pump

   If the code persists on models where the injection pump has an internal speed sensor, the issue could be internal wear (such as cam bearing wear causing the sensor wheel to rub against the sensor). Replace the injection pump if internal wear is confirmed.

3. 3

   Clear codes and test operation

   After any repair or replacement, clear the stored diagnostic codes and operate the machine to ensure the fault does not return.