P1128: Closed Loop Fueling Not Achieved, Bank 1
4 vehicles · 2 makes · $40-$180 repair
Most Reported On
P1128 is an OBD-II diagnostic trouble code meaning “Closed Loop Fueling Not Achieved, Bank 1.” A Chrysler/Dodge/Jeep/Ram manufacturer-specific code. The powertrain control module never saw the Bank 1 upstream oxygen sensor reach the conditions needed to switch from open loop (preprogrammed fuel mixture) into closed loop (mixture corrected from live sensor data) within the allowed time. Running in open loop means the engine is guessing at fuel delivery, so expect worse fuel economy, rough running, and a failed emissions test. Other makes assign P1128 to entirely different faults - Honda uses it for "MAP Sensor Signal Lower Than Expected" and Ford uses it for upstream O2 sensor connectors swapped bank to bank - so confirm against the make. This code is most commonly reported on 2014-2025 Audi SQ5, 2009-2025 Audi Q5, and 1996-1999 Honda Civic, plus 1 other vehicle, with repair costs ranging from $40 to $180.
Common Causes
Typical Repair Cost
Based on 4 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
P1128 does not use the standard P/B/C/U prefix. It may be a manufacturer-specific code, so verify that a scanner supports your exact year, model and module before buying.
Vehicles Affected (4)
FAQ
What does P1128 mean?
P1128 stands for "Closed Loop Fueling Not Achieved, Bank 1." A Chrysler/Dodge/Jeep/Ram manufacturer-specific code. The powertrain control module never saw the Bank 1 upstream oxygen sensor reach the conditions needed to switch from open loop (preprogrammed fuel mixture) into closed loop (mixture corrected from live sensor data) within the allowed time. Running in open loop means the engine is guessing at fuel delivery, so expect worse fuel economy, rough running, and a failed emissions test. Other makes assign P1128 to entirely different faults - Honda uses it for "MAP Sensor Signal Lower Than Expected" and Ford uses it for upstream O2 sensor connectors swapped bank to bank - so confirm against the make.
What are the most common causes of P1128?
The most common causes of P1128 are: Failed or slow-responding upstream (Bank 1) oxygen sensor, Weak fuel delivery - clogged fuel pump strainer, weak pump, or restricted filter, Engine thermostat stuck open, so the engine never reaches operating temperature, Exhaust leak ahead of the upstream O2 sensor, Failed MAP, MAF, or intake air temperature sensor, Wiring or connector faults in the O2 sensor circuit. The specific cause varies by vehicle.
How much does it cost to fix P1128?
Repair costs for P1128 range from $40 to $180, depending on the vehicle and root cause.
Which vehicles are affected by P1128?
Au7o has documented P1128 across 4 vehicle models from 2 manufacturers: Audi, Honda.
Sources (5)
- TSBAudi TSB 2014753/13 - Gasoline Quality, Misfire, Lean-System and Deposit Diagnosis
- TSBAudi TSB 2075515/2 - Fuel Additives Not Permitted for EA839 V6 TFSI
- articleTroubleshootMyVehicle - How To Test The MAP Sensor (1995-2000 1.6L Honda Civic)
- articleMyProStreet - P1129 Honda 1.6L - How To Test a MAP Sensor
- ForumHonda-Tech - D16z6 map sensor code
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.