P219B is a generic OBD2 trouble code. This code indicates that your Mazda 3’s air/fuel ratio is out of balance (too rich or too lean) on the bank 2 side of the engine in question.
Your 3 is equipped with oxygen sensors that measure the air-fuel ratio of your engine. It’s these sensors that are reporting the problem with the air-fuel ratio to the PCM.
When diagnosing P219B, there are two scenarios. The first is that the oxygen sensors are correct and the air-fuel ratio is off. The second is that the oxygen sensors are giving incorrect data, and they need to be replaced.
P219B Definition: Air Fuel Ratio Imbalance – Bank 2
The definition of P219B has two parts and is fairly straightforward.
1. Air Fuel Ratio- Imbalance
The ideal air/fuel ratio for a gas engine is 14.7 parts air to 1 part fuel (14.7:1). If there is too much fuel or too much air in the mixture, the ratio is too rich or too lean. P219B does not specify if your 3’s air-fuel ratio is too rich or too lean. There will likely be another code that will provide this information (P219B rarely appears by itself).
2. Bank 2
There is a bank of cylinders on each side of your 3’s engine. Bank 2 is the side of the engine with the second cylinder. If bank one had an imbalanced air/fuel ratio, the code in question would be P219A.
You need to determine which side of the engine bank 2 is on.
While it can be annoying trying to determine which side of the engine bank two is on, it makes the diagnosis a little easier since we can use the swap test (more on that later).
P219B Symptoms: Mazda 3
Often, the only sign that your 3 has P219B is the check engine light. Here are some of the symptoms that can occur:
- Engine Misfire– This can be noticeable misfiring. But, it’s more likely that you’ll only know of the misfiring due to the presence of another trouble code. You’ll likely see either P0300 or P030X, where the X represents the cylinder that is misfiring. Example: P0301 is a misfire in the first cylinder.
- Check Engine Light– As stated above, the check engine light is often the only symptom of P219B. But, this code is most likely going to be accompanied by another code. This is a good thing. Other codes can help with the process of elimination. You’ll likely get a lean or rich trouble code with P219B, such as P0174. You could also see a MAF-related code or oxygen sensor-related code.
- Decreased Fuel Economy– There may or may not be a drop in fuel economy and engine performance with P219B.
Mazda 3 P219B: Causes + Diagnosis
Here is how you can go about diagnosing P219B in your 3 at home:
1. Check for Other Codes
P219B is usually accompanied by other trouble codes, which can really help with diagnosing it. As you can see in the symptom section above, many codes can accompany P219B.
Address all of the other codes first. P219B will usually resolve itself along with resolving the other codes.
2. Check for Exhaust Leaks
An exhaust leak can cause an oxygen sensor to report that the air-fuel mixture is off. That’s because the exhaust is escaping without ever passing over the O2 sensor(s).
Sometimes leaking exhaust can be obvious. You’ll hear it. Sometimes, not so much. Take a look under your 3 at the exhaust and see if there are any soot marks where the exhaust is escaping.
3. Inspect the Oxygen Sensor Wiring
Taking a quick look at the oxygen sensor wiring can save you a lot of trouble. The wiring to the sensor(s) has a hard life. Take a look and make sure that it is not cracked or damaged in any way.
An open/short condition can cause an oxygen sensor to send inaccurate data to the PCM/ECM. It only takes a moment and can save a lot of frustration. Repair the harness as necessary.
4. Swap Test
While it may have been annoying to determine which side of the engine bank two was on, it does come with a big advantage. You can swap the oxygen sensors (between the catalytic converter and the engine) to the other side of the exhaust and see if the code “jumps” to the other side of the engine.
Clear the codes after swapping them. Once you run the engine for a while, P219B should appear if an O2 sensor was causing the problem. If P219B comes back, we know that the O2 sensors are all working correctly and that the problem is more than likely related to the motor. Think vacuum leak, MAF, or bad injector.
It can be tough trying to chase down P219B in the Mazda 3 by itself. So we always recommend taking a look at the other codes first. Good luck!