Fault code P1128 – a step-by-step guide to diagnosing and fixing it

Error code P1128 is displayed and the check engine light is on - what does this mean?

The DTC P1128 is recognized by the OBD system when there is a problem with the fuel supply or the air-fuel mixture. This manufacturer-specific error code mainly occurs in vehicles with a lean mixture or insufficient fuel supply. Depending on the manufacturer, the P1128 code can have different specific meanings, but generally refers to problems in the fuel system or with the mixture formation.

What causes can this error code have?

• Defective fuel pump
• Clogged fuel filter
• Damaged fuel injectors
• Defective fuel pressure regulator
• Leaking fuel lines
• Dirty or defective lambda sensors
• Problems with the mass air flow sensor
• Clogged air filter
• Leaks in the intake system
• Defective fuel pressure sensors

What symptoms occur in parallel with fault code P1128?

• Starting problems: The vehicle is difficult to start or does not start at all
• Loss of power: Significantly reduced engine power, especially when accelerating
• Smooth idling: Engine runs unevenly or stutters when idling
• Increased fuel consumption: Noticeably higher consumption than usual
• Jerking while driving: Engine jerks or does not pull smoothly
• Exhaust problems: Unusual exhaust values or odors

How can you fix the problem with error code P1128?

• Repairing the P1128 error code requires a systematic diagnosis of the fuel supply and the mixture formation system.
• Check and replace the fuel pump and fuel filter: Measure fuel pressure, replace fuel pump if pressure is too low and replace fuel filter at the same time
• Clean or replace fuel injectors: Remove injectors, have them professionally cleaned or replace with new injectors if defective
• Check and replace lambda sensors: Check lambda sensor signals with diagnostic device and replace defective sensors with new ones
• Clean or replace the mass air flow sensor: Clean MAF sensor with special cleaner or replace completely if defective
• Check intake system for leaks: Check all hoses and connections between air filter and engine for cracks or loose connections and seal them
• Replace fuel pressure regulator: Check fuel pressure regulator and replace with a new part if defective