Kubota P0171 – Engine Control Module (ECM): Adaptive Learn Bank 1 High (Gasoline)

This code indicates a "System Too Lean" condition on Bank 1 of the engine. The Engine Control Module (ECM) has detected that the air-fuel mixture contains too much air and not enough fuel. The ECM attempts to compensate by adding more fuel, and when the adaptive learning threshold exceeds its maximum limit, the system triggers P0171 and may initiate a "Power Derate 1" mode.

• Kubota WG1605-G-E3
• Kubota WG1605-L-E3
• Kubota WG1605-GL-E3
• Haulotte HA16RTJ Pro
• Haulotte HA26 RTJ Pro
• Advance SC8000
• Bartell Global Terminators
• Merit M500SS

1. 1

   Check for and diagnose any other active Diagnostic Trouble Codes (DTCs) first

2. 2

   Inspect the intake tract, manifold gaskets, and vacuum hoses for leaks that could introduce unmetered air

3. 3

   Test fuel supply pressure and check for a faulty pressure regulator

4. 4

   Check the Pre-Catalyst Oxygen Sensor wiring to ensure it is not mispositioned, contacting hot exhaust, or shorted to ground

5. 5

   Check for a dirty or stuck-closed fuel injector

6. 6

   Check the ignition system for a weak spark or lack of spark to a cylinder

7. 7

   Verify the TMAP (Temperature/Manifold Absolute Pressure) sensor is reading correctly

1. 1

   Scan and Verify

   Connect a diagnostic scanner to the diagnostic connector to confirm P0171. Monitor live data for the Bank 1 Sensor 1 (upstream) O2 sensor voltage and fuel trim percentages.

2. 2

   Inspect Intake System

   Visually inspect all air intake hoses and the throttle body assembly. Tighten any loose clamps and replace cracked hoses to eliminate vacuum leaks.

3. 3

   Clean the TMAP Sensor

   Remove the TMAP sensor and clean it carefully with a dedicated sensor cleaner. Reinstall and check if the fuel trims normalize.

4. 4

   Test Fuel Delivery

   Connect a fuel pressure gauge to the fuel rail. Verify that the electric fuel pump is delivering the correct pressure specified in your machine's manual. If pressure is low, inspect the fuel filter and fuel pump.

5. 5

   Inspect/Replace O2 Sensor

   If the upstream O2 sensor is unresponsive or reads a continuous low voltage (indicating lean) despite adding fuel, inspect the harness for melted wires. If the wiring is intact, replace the Pre-Catalyst O2 sensor.

6. 6

   Service Fuel Injectors

   If fuel pressure and sensors are good, a dirty or stuck-closed fuel injector is likely the culprit. Remove the fuel rail and inspect the injectors. Clean or replace the affected injector.

7. 7

   Clear and Test

   Clear the ECM fault codes. Run the engine under load to ensure the check engine light remains off and the machine no longer operates in derate mode.