P1128 on Audi
Closed Loop Fueling Not Achieved, Bank 1
P1128 on Audi vehicles indicates closed loop fueling not achieved, bank 1. Au7o has documented this code across 3 Audi models — most commonly on A4, Q5, SQ5. 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.
Common Causes of P1128
- •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
P1128 on Audi by Model
Audi A4(1 issue)
- 2009-2021 A4 2.0T Gasoline-Quality Deposit Diagnosis - TSB 2014753/132009-2021
Audi states that contaminated gasoline or gasoline with insufficient deposit-control additives can contribute to deposits on intake valves, the intake manifold, fuel injectors and combustion chambers. Possible results include rough running after cold start, extended cranking, hesitation, rough idle, reduced performance, poor fuel economy or an MIL with supported misfire, lean-system or cylinder-imbalance faults. This does not establish a universal A4 2.0T intake-valve defect, mandatory walnut-blasting interval or fixed failure mileage.
Audi Q5(1 issue)
- 2009-2025 Q5 Gasoline-Quality Deposit Diagnosis - TSB 2014753/132009-2025
Audi states that contaminated gasoline or gasoline with insufficient deposit-control additives can contribute to deposits on intake valves, the intake manifold, fuel injectors and combustion chambers. Possible results include rough running after cold start, extended cranking, hesitation, rough idle, reduced performance, poor fuel economy or an MIL with misfire, lean-system or air/fuel-ratio-imbalance faults. This does not establish a universal Q5 intake-valve defect, a mandatory walnut-blasting interval or a fixed failure mileage.
Audi SQ5(1 issue)
- Fuel-Quality or Deposit-Related Rough Running and Misfire Diagnosis2014-2025
Audi states that contaminated gasoline or gasoline with insufficient deposit-control additives can contribute to deposits in injectors, combustion chambers, the intake manifold and intake valves, with rough running, hesitation, reduced performance, poor fuel economy or related ECM faults. This does not establish a universal SQ5 intake-valve defect, a mandatory walnut-blasting interval or a fixed mileage. Audi separately warns that unapproved fuel additives are not permitted on 2018-2025 EA839 V6 TFSI SQ5 models because a negative effect on engine life cannot be ruled out.
Looking for P1128 on a different make?
View P1128 across all makes →Frequently Asked Questions
What does P1128 mean on Audi?▼
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. On Audi specifically, this code is documented across 3 models.
What causes P1128 on Audi vehicles?▼
Common causes on Audi: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P1128 on a Audi?▼
Repair costs vary widely depending on the root cause and specific Audi model.
Which Audi models have P1128 documented?▼
Au7o has documented P1128 on 3 Audi models: A4, Q5, SQ5.