Your ride’s fuel system delivers fuel to the engine as needed. It has critical components like the fuel pump, fuel tank, fuel filter, and injectors. If a problem develops in the fuel management system, your vehicle might log a P1128 code.
Diagnostic trouble code (DTC) P1128 stands for “Closed Loop Fuel Not Achieved Bank 1.”
This code is logged when the powertrain control module (PCM) detects an issue in the fuel system that’s causing it to stay in open-loop operation within the timeframe set by your manufacturer.
Code P1128 can point to an issue with the sensor, the wiring or the PCM. In some cases, other factors affecting the air-fuel mixture can cause the entire system to remain in open loop but there will typically be noticeable symptoms in a case like this.
“Bank 1” means that the issue is in the first bank of cylinders in a V-type engine. A P1128 code can also indicate that the heated oxygen (O2) sensors in your engine are malfunctioning.
Closed loop fuel control is achieved very soon after the engine starts due to oxygen sensor heaters bringing the sensors online as quickly as possible. But wide open throttle (WOT) is an open loop mode by default due to the engine’s need for maximum fuel delivery at that point.
Closed loop fuel control is achieved very soon after the engine starts due to oxygen sensor heaters bringing the sensors online as quickly as possible. But wide open throttle (WOT) is an open loop mode by default due to the engine’s need for maximum fuel delivery at that point.
–Richard McCuistian, ASE Certified Master Automobile Technician
Note: The definition of code P1128 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.
The P1128 is a manufacturer-specific code, so there’s no universal diagnostic procedure that would work for all vehicles. After all, vehicles can be structured differently depending on their manufacturer.
If you’re not sure how to diagnose the issue, it’s best to take your vehicle to an auto repair shop for a proper diagnosis. Otherwise, you can do it yourself.
Resolving a P1128 isn’t easy, especially if you don’t have in-depth knowledge of the fuel management system. Your best option is to let a licensed mechanic fix the problem for you.
But if you’re confident that you can resolve the trouble code on your own, make sure to read up about this trouble code before you do anything with your vehicle. Resources like Chilton can give you vehicle-specific information that can help you fix code P1128.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.