P1128 Long-term fuel trim too lean, multiplicative (bank 1)

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

P1128 means: Long-term fuel trim too lean, multiplicative (bank 1). The mixture has too little fuel or too much air, and the computer can no longer correct it on its own. Drive gently and have the car checked soon. The most common repair costs about €60–120 in Estonia, depending on make and model.

What it means

The mixture has too little fuel or too much air, and the computer can no longer correct 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: Throttle control motor locked.

What you may notice

• Engine light on
• Rough idle
• Hesitation when accelerating
• The engine may stall

What could be wrong

1. 1Air leak (vacuum hose, intake gasket, crankcase breather) · Vacuum hose or actuator replacement €60–120
2. 2Dirty or faulty mass air flow sensor · MAF sensor replacement €120–240
3. 3Weak fuel pump or clogged fuel filter · Fuel pump replacement €250–500
4. 4Clogged injector · Injector replacement €200–400
5. 5Exhaust leak before the oxygen sensor · Oxygen sensor replacement €90–180

Repair difficulty: Moderate

What you can check yourself

Listen at idle for a hiss. Check the vacuum hoses, especially old, cracked ones. You can check the simple things yourself, but the repair is best done in a workshop.

How we fix it

1. We check the fuel trims on the diagnostic tool
2. We do a smoke test to find the air leak
3. We measure fuel pressure and check the MAF sensor
4. We replace the leaking hose, gasket or faulty part

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