P1126

What it means

On Volkswagen, P1126 means the engine control unit has found that the long term fuel trim on bank 2 has reached its limit in the lean direction, with the 'add air' side of the adaptation too lean. The ECU is adding as much fuel as it is allowed to but still cannot bring the mixture on bank 2 to target, so it sets the code. The exact trim range and the engines affected vary by model and year, so check the manufacturer's data for the specific engine.

Symptoms

• Engine management light on
• Rough or unstable idle
• Hesitation or poor response under load
• Slightly higher fuel consumption
• Possible fuel trim or lean-mixture faults stored alongside this code

Possible causes

• Unmetered air entering the intake on bank 2 (split hose, loose clip, leaking intake manifold gasket)likely
• Leaking or perished vacuum hose, brake servo hose or crankcase breather hose on the bank 2 sidelikely
• Faulty or contaminated mass airflow sensor giving a false readingpossible
• Restricted or failing fuel injector on bank 2, or low fuel pressurepossible
• Exhaust leak upstream of the bank 2 oxygen sensor letting in air and giving a false lean readingpossible
• Faulty bank 2 oxygen sensor or its wiring and connectorpossible
• Outdated engine control unit software where the manufacturer has issued a correction for this faultrare

How to diagnose

1. Read all stored codes and freeze frame data, noting engine temperature, load and fuel trim values when the code set
2. Look over the intake pipework, hoses, clips and breather connections for splits, disconnection or perishing, especially on the bank 2 side
3. Check live short and long term fuel trims for both banks at idle and at about 2500 rpm to see whether the lean condition is idle-only or load-related
4. Check the mass airflow sensor reading against expected values and inspect the sensor and its connector for contamination or damage
5. Smoke test the intake system and crankcase ventilation to find small air leaks
6. Inspect the exhaust upstream of the bank 2 oxygen sensor for leaks and check the sensor wiring and connector
7. Test fuel pressure and compare injector performance between banks, following the procedure for the specific engine
8. Check whether a software update is listed for the engine and fault for this model

How to fix

• Repair or replace leaking intake hoses, clips, manifold gaskets or seals
• Replace perished vacuum or crankcase breather hoses and any faulty ventilation components
• Replace the mass airflow sensor if testing shows it is reading incorrectly
• Clean or replace faulty fuel injectors and correct any fuel pressure problem
• Repair exhaust leaks upstream of the oxygen sensor, or replace the bank 2 oxygen sensor or repair its wiring if proven faulty
• Apply a manufacturer software update only if one is confirmed for this fault

Can I keep driving?

This code for other makes

• P1126LexusMagnetic Clutch Circuit Malfunction
• P1126MazdaThrottle Position Narrow Range Sensor Circuit
• P1126NissanThermostat Function
• P1126OtherThrottle Position (Narrow Range) Sensor Circuit Malfunction
• P1126ToyotaMagnetic Clutch Circuit

Nearby codes

• P1125VolkswagenLong Term Fuel Trim Add Air Bank 2 System Too Rich
• P1127VolkswagenLong Term Fuel Trim Bank 1 System Too Rich