Kubota P1166 – Engine Control Module (ECM) / Engine ECU: Catalyst inactive on NG

The catalytic converter is not functioning properly (inactive) when the engine is running on Natural Gas (NG) or LPG. The ECM monitors the efficiency of the catalyst by comparing the signal from the pre-catalyst oxygen sensor to the post-catalyst oxygen sensor. If the post-catalyst sensor waveform mirrors the pre-catalyst sensor too closely, it means the catalyst is no longer storing and releasing oxygen effectively.

• WG1605
• WG1903
• WG2503
• WG3800

1. 1

   Check the wiring harness for the Bank 1 Sensor 2 (post-catalyst) oxygen sensor for any opens, shorts, or physical damage.

2. 2

   Verify that the post-catalyst O2 sensor signal wire is not shorted to the pre-catalyst O2 sensor signal wire.

3. 3

   Check if the O2 signal wire is open or shorted to ground, and ensure the feed circuit to the O2 heater is intact.

4. 4

   Inspect the catalytic converter/muffler assembly for severe physical damage, exhaust leaks, or signs of internal contamination.

1. 1

   Clear and Retest

   Clear the code and run the engine's Closed Loop (CL) test using the Kubota Diagnostic Tool (KGST/DST-i) to verify if the fault is active.

2. 2

   Inspect and Repair Wiring

   If wiring faults are found during the diagnostic checks (e.g., melted wires touching the exhaust), repair the harness and ensure the sensor is properly positioned.

3. 3

   Test/Replace the O2 Sensor

   If the wiring is intact but the post-catalyst O2 sensor is unresponsive or the heater circuit has failed, replace the Bank 1 Sensor 2 Oxygen Sensor.

4. 4

   Replace the Catalytic Converter

   If the O2 sensors and wiring are functioning perfectly, the catalyst element itself is depleted, contaminated, or physically damaged. You must replace the catalytic converter/muffler assembly. Note: When replacing the catalyst on Kubota E3 engines, you must record the catalyst identification numbers (part number, manufacturing date, and lot number) from the new unit's barcode tag for EPA compliance tracking.