P2179 OBD-II Trouble Code: System Too Lean Off Idle Bank 2

Check Engine Light

P2179 code definition

System Too Lean Off Idle Bank 2

What the P2179 code means

This code indicates that there is a lean air fuel mixture on bank 2 of the engine. Bank 2 refers to the set of cylinders that does not contain cylinder number one.

What causes the P2179 code?

Two possibilities include a vacuum leak on bank 2 or a problem with the induction monitoring system. The induction system consists of the intake manifold and sensors that the Powertrain Control Module (PCM) uses to calculate air fuel ratio. If any of these sensors are not working within specification, the PCM will not be able to calculate the air fuel ratio correctly and therefore, the system will believe there is a lean running condition.

Another possible cause of this code is a problem with a fuel injector or the circuit that fires it. A faulty or clogged fuel injector will not be able to supply enough fuel to the cylinder it supplies. The PCM turns the injector on and off, allowing fuel to pass through it into the cylinder. The PCM has a driver for each injector. At times, a driver or two will fail and the PCM will need to be replaced. If there is a fuel supply problem like this, introducing propane into the intake manifold will make the motor run smoothly. Determining why the injector is not performing as it should is another process.

What are the symptoms of the P2179 code?

The Check Engine Light will be illuminated and there will be a variety of drivability symptoms, such as:

  • High idle misfires
  • Low power output
  • Dying hard start

How does a mechanic diagnose the P2179 code?

As with any code, the technician must connect a scanner, review codes and monitor scan tool data. The first problem to suspect is an intake manifold leak. This should be thoroughly investigated before any other diagnostics are done. If there are not any vacuum leaks, the next thing to look at is the bank 2 O2 (oxygen sensor).

The O2 sensor is what the PCM uses to determine what is happening in the combustion chamber. The most effective way to test an oxygen sensor is to introduce a rich mixture into the intake manifold while watching the scan data. When operating normally, an O2 sensor should oscillate quickly within its voltage range. If this code is set, the O2 sensor will not oscillate. By introducing a rich mixture of propane into the intake, the O2 sensor voltage should react accordingly. If it reacts as it should, it can be determined that the O2 sensor is sending accurate data to the PCM and there is actually a problem with the fuel mixture.

If the O2 sensor for bank 2 is working, the next thing to suspect is an injector problem. This can be in the form of clogging, injector internal electrical failure or a problem with the injector driver in the PCM. Unclogging an injector requires a bit of effort, so before the mechanic dives into that, it is prudent to be sure the PCM is firing the injector electrically as it should. This is done simply with what is called a noid light. It is plugged into the injector connector in place of the injector. If it is working properly, it should flash rapidly, if not, a simple check for power is necessary.

If there is power, then the PCM is faulty because the PCM supplies a ground to the injector circuit, in order to fire the injector. If the PCM is working correctly, the technician can choose to replace the injector or attempt to unclog it. This is best done with a machine that runs a concentrated version of injector cleaner through the fuel system. It is much more effective than dumping a cleaner into your fuel tank. Which option the technician chooses is a factor of the mileage, general condition of the vehicle and a conversation with the customer.

If all that has proven to be in good working condition, it is time to take a closer look at the other sensors in the induction system. The induction system is the intake manifold and all the components attached to it, involved with the delivery of an air fuel mixture to the combustion chamber. Some systems utilize Mass Air Flow (MAF) sensors that measure the amount of air entering the intake manifold and others use Manifold Absolute Pressure (MAP) sensors to measure the pressure in the intake manifold. No matter the system, these two components are primary components for the PCM to determine how much fuel should be injected into the motor. The technician should look at the data they produce as well as performing manufacturer specific tests at each sensor.

Common mistakes when diagnosing the P2179 code

Modern vehicles have complicated induction systems with many points of failure. Not to mention the systems attached to the intake manifold utilizing the vacuum inside. Many times vacuum leaks are not always obvious and take some perseverance and ingenuity to locate. Part of being an experienced technician is knowing when we have done due diligence and it’s time to move onto the next test. Simply said, it is very easy to miss a vacuum leak.

It’s important to understand, the computer extrapolates the presence of a lean condition in the induction system on bank 2. The strategy used to determine this depends on the manufacturer and the specific system being worked on. Understanding how the computer comes to the conclusion there is a lean condition is vitally important in a successful diagnosis. The diagnosing of codes like this is usually left to more experienced technicians. It is easy to misinterpret what the PCM is doing and make a wrong diagnosis.

How serious is the P2179 code?

This code usually isn’t very serious. I have seen this code and codes like this set without any symptoms other than the Check Engine Light. If there are symptoms, the worse the vehicle runs will be an indicator of how serious the this code is. Most often an owner will seek help when their vehicle is running badly. It is possible to burn valves if driven to far when running badly.

What repairs can fix the P2179 code?

Additional comments for consideration regarding the P2179 code

There are many possible causes for a code like this, which can be quite complex to diagnose. A thorough understanding of the system being worked on is paramount to a successful diagnosis of this kind. It’s important for the technician to do some extra homework when such a code is presented to him or her. It is not the number of possible causes that is the complexity, but the complexity is that the failed component doesn’t always show a clear sign of failure. For this reason, less experienced technicians don’t usually find themselves diagnosing a code such as this. It is time under the hood that eventually leads to a quick and decisive repair. Even so, this type of problem is often elusive for the most experienced technician.

Need help with a P2179 code?

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