P1129 Long-term fuel trim too rich, multiplicative (bank 1)

By: Diagno editorial team · Updated: 2026-10-15

P1129 means: Long-term fuel trim too rich, multiplicative (bank 1). There is too much fuel in the mixture and the computer can no longer reduce it on its own. Drive gently and have the car checked soon. The most common repair costs about €200–400 in Estonia, depending on make and model.

What it means

There is too much fuel in the mixture and the computer can no longer reduce it on its own.

This is a make-specific code (VAG). The exact meaning can vary by model and year. On other makes the same code means: Toyota: Electronic throttle control system fault.

What you may notice

• Engine light on
• Higher fuel consumption
• Black smoke or fuel smell from the exhaust
• Sooty spark plugs

What could be wrong

1. 1Leaking injector · Injector replacement €200–400
2. 2Fuel pressure too high · Fuel system check €45–90
3. 3Mass air flow sensor reading wrong · MAF sensor replacement €120–240
4. 4Clogged air filter · Air filter replacement €25–50
5. 5Faulty oxygen sensor · Oxygen sensor replacement €90–180

Repair difficulty: Moderate

What you can check yourself

Check that the air filter is clean. Notice whether the exhaust smells of fuel. You can check the simple things yourself, but the repair is best done in a workshop.

How we fix it

1. We check fuel trims and sensor readings on the diagnostic tool
2. We measure fuel pressure
3. We check the injectors for leaks
4. We replace the faulty part

Standard SAE description: Long Term Fuel Trim mult., Bank 1 System too Rich