P1128Fuel & Air Metering

Closed Loop Fuel Mixture Not Achieved, Bank 1 (VW/Audi)

P1128 is a VW/Audi code meaning the long-term fuel trim on Bank 1 is out of range on the lean side (closed loop mixture too lean). It commonly points to a vacuum leak, MAF issue, or fuel delivery problem.

🚗 Yes, short-term, but expect worse fuel economy and drivability issues.

MEDIUM

severity

🎯 Top Causes, Ranked by Likelihood

#1Vacuum or intake leak$50-$400

45%

Unmetered air leans the mixture; check intake boots and PCV.

#2Dirty or failing MAF sensor$50-$350

30%

An underreading MAF causes a lean condition.

#3Low fuel pressure or weak injectors$50-$600

25%

Insufficient fuel delivery leans the mixture.

🩺 Common Symptoms

Check engine light
Rough idle
Reduced fuel economy
Hesitation on acceleration

💰 Repair Cost: DIY vs Shop

DIY Cost

$50-$400

Shop Cost

$150-$600

📋 Free OBD2 Code Cheat Sheet

The 50 most common codes with likely cause and DIY fix cost. Sent once, no spam.

🔧 How to Diagnose P1128

1Smoke-test for vacuum and intake leaks

2Clean or test the MAF sensor

3Check fuel pressure and injector operation

4Review fuel trims after repairs

❓ Frequently Asked Questions

Can I drive with P1128?

Short-term yes, but a lean mixture hurts economy and drivability. Diagnose within a week or two.

Is P1128 a VW/Audi code?

Yes, P1128 is a VW/Audi lean fuel mixture code for Bank 1 closed loop control.

What causes P1128?

A vacuum leak, a dirty or failing MAF, or low fuel pressure are the most common causes.

🔗 Related Codes

P1136P0171P0172P0101