Symptoms
With the wide range of possibilities, the listed issues may or may not be present. However, this is where it is important to pay close attention to the observed symptoms and note what and when symptoms appear for the diagnostic strategy.
- Vehicle misfires at idle
- Hard to start, especially when hot
- Very irregular idle
- Additional codes to identify the cause of the original P2189 code
- Hissing noises
- Lower turbo boost numbers
- Fuel smell
Potential Causes of P2189 DTC
- Faulty O2 sensor (front)
- Faulty fuel cap seal
- Leaking or loose oil filler cap
- Air leak in the intake manifold downstream of the mass air flow sensor due to the manifold itself, disconnected or cracked vacuum hoses, leaking MAP sensor, leak at the turbo bypass or it is stuck open, brake booster hose, or a leak in the EVAP system hoses.
- Faulty MAP sensor
- EVAP purge valve
- Fuel injector leak
- Faulty fuel pressure regulator
- Leaks in the exhaust system
- Faulty variable camshaft timing
- Faulty ECM (engine management computer)
- Faulty O2 heater (front)
- Clogged fuel filter
- Fuel pump wearing out and producing low pressure.
- Faulty mass air flow sensor
Diagnostic Steps / Repair
Your strategy to locate this problem starts with a road test and observing any symptoms. The next step is to use a code scanner (available at any auto parts store) and retrieve all additional codes.
The computer has set a P2189 code indicating that the fuel mixture is lean at idle. This is the main code; however, any faulty component in this loop that has the potential to cause a lean mixture will also be set in the code.
If the road test produces no symptoms, it may not be a real code. In other words, the fuel mixture is not lean, and the computer or oxygen sensor is responsible for setting the code.
Each vehicle has a minimum of two oxygen sensors—one in front of the catalytic converter and one after the converter. These sensors report the amount of free oxygen remaining in the exhaust gases after ignition, which determines the fuel ratio. The front sensor is primarily responsible for the mixture; the second sensor behind the exhaust is used for comparison with the front sensor to determine if the converter is functioning properly.
If a rough idle is present or any of the other symptoms, start the process first with the most likely cause. Either unmetered air is entering the intake manifold, or there is a lack of fuel pressure:
- Check the fuel cap for cracks, seal, and function
- Lift the hood and ensure the oil filler cap is tight
- If additional codes were present, start by inspecting them first
- Look for air leaks starting from the mass air flow sensor. Check the hose or connection between the sensor and the intake manifold for cracks or loose connections. Check all vacuum hoses securely attached to the intake manifold, including the one from the brake booster. Check the MAP sensor hose and all turbo hoses, if applicable.
- With the engine running, use a can of carburetor cleaner and spray a fine mist around the base of the intake manifold and where the two halves meet if it is a two-piece unit. Spray around the base of the EGR for leaks in the manifold. The RPM will increase if a leak is found.
- Check the PCV valve and hose for leaks.
- Inspect fuel injectors for external fuel leaks
- Inspect the fuel pressure regulator by removing the vacuum hose and shaking it to see if there is fuel. If so, replace it.
Stop the engine and install a fuel pressure tester on the Schrader valve on the fuel rail of the injectors. Start the engine and note the fuel pressure at idle and again at 2500 RPM. Compare these numbers with the desired fuel pressure found online for your vehicle. If outside the volume or pressure, replace the pump or filter.