Code Definition: P1129 - Fuel Trim Bank 2 Too Lean
The P1129 code is a generic trouble code that indicates the engine's fuel trim system has detected a lean fuel condition in bank 2. This code is typically triggered when the engine's computer detects that the fuel mixture is too lean, meaning there is more air than fuel entering the engine's combustion chamber.
Possible Causes:
- Faulty fuel injector(s)
- Clogged or dirty fuel injector(s)
- Low fuel pressure
- Faulty fuel pressure regulator
- Vacuum leaks
- Faulty MAF (Mass Airflow Sensor)
- Faulty TPS (Throttle Position Sensor)
- Faulty IAT (Intake Air Temperature) sensor
- ECU software glitch
Symptoms:
- Illuminated check engine light
- Poor engine performance
- Rough idling
- Stumbling or hesitation during acceleration
- Decreased fuel efficiency
- Increased emissions
Diagnostic Procedure:
- Use a scan tool to retrieve the trouble code and view the freeze frame data to determine when the code was set and under what operating conditions.
- Check for any other trouble codes that may be present, as they may provide additional information about the problem.
- Inspect the fuel injectors and their connections for signs of damage or corrosion.
- Measure the fuel pressure using a gauge to ensure it falls within the manufacturer's specifications.
- Inspect the intake system for vacuum leaks or other issues that could affect the air/fuel ratio.
- Test the MAF, TPS, and IAT sensors to ensure they are functioning correctly.
- Use a scope to inspect the fuel injector pulse width and compare it to the manufacturer's reference pattern.
- Clear the code and perform a road test to see if the condition persists. If the code does not return, the problem may have been intermittent or related to a loose connection.
- If the code returns, continue troubleshooting by performing additional tests as needed based on the suspected cause.
Repair Information:
- Replace any faulty or clogged fuel injectors.
- Clean or replace the fuel injector harness and connectors if necessary.
- Replace the fuel pressure regulator if it is faulty.
- Repair any vacuum leaks in the intake system.
- Replace the MAF, TPS, or IAT sensor if it is faulty.
- Update the ECU software if necessary.
- Adjust the fuel trim values if necessary.
