| Bank 1 Air/Fuel Ratio Imbalance
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Table of Contents
- What Does Code P219A Mean?
- Where is the P219A sensor located?
- What are the common causes of code P219A?
- What are the symptoms of code P219A?
- Get Help with P219A
What Does Code P219A Mean?
OBD II fault code P219A is a generic code that is defined as “Bank 1 Air/Fuel Ratio Imbalance”, or sometimes as “Mixture Control Bank 1 – Value Out Of Range”, and is set when the PCM (Powertrain Control Module) detects an imbalance in the air/fuel mixture between individual cylinders on Bank 1. Note that “Bank 1” refers to the bank of cylinders on V-type engines that contains cylinder #1.
SPECIAL NOTES: Note that neither this code, nor any of its closely related codes, which are P219C, P219D, P219E, and P219F should be confused with any other air/fuel ratio related codes, even though there are some similarities between these codes and “normal” air/fuel ratio related codes in terms of both their causes and effects.
The codes listed immediately above all relate to air/air fuel imbalances between individual cylinders on a given cylinder bank, as opposed to air/fuel ratio issues that affect all the cylinders on a given cylinder bank equally. In the case of code P219A, the code refers to an issue that causes a rich condition (too much fuel relative to air) in one or more cylinders on Bank 1, as opposed to an issue that causes a lean condition (too much air relative to fuel) in one or more cylinders on Bank 1. END OF SPECIAL NOTES.
Although modern engine and fuel management systems have reached high levels of sophistication, and are generally capable of fine control of air/fuel mixtures, these systems cannot measure or monitor the air/fuel mixture in each individual cylinder directly. Put in another way, modern engine and fuel management systems cannot account, and compensate for factors that influence how much fuel relative to air enters any given cylinder on the one hand, and how efficiently that air/fuel mixture is combusted in any given cylinder, on the other.
On a fully functional engine that is in good mechanical condition, the engine management system assumes that the volumes of all cylinders are equal, that all cylinders develop the same compression pressure, that all ignition sparks are of the same intensity, and that the exhaust gas is extracted equally efficiently from all cylinders.
Based on these assumptions, the PCM calculates how much fuel to inject into each cylinder at any given point in an engines’ operating range, these calculations in their turn being based on input data from various sensors. Typically, these sensors include the throttle position sensor, MAF/MAP sensor, engine coolant and intake air temperature sensors, and the engine speed sensor, among many others. In practice, and if all these sensors and their associated systems work as designed, the engine will run smoothly and efficiently, and emissions can therefore be controlled fairly accurately.
However, no engine is ever in perfect condition, but in practice, engine management systems are programmed to “ignore” minor issues like differences in the manufacturing tolerances of parts like fuel injectors, which differences can produce small deviations between the desired and actual volumes of fuel that each injector injects under different operating conditions.
Nonetheless, slight differences in fuel injection volumes, compression pressures, and ignition spark intensities between cylinders can worsen over time until eventually, the differences start to approach or exceed maximum allowable thresholds, which when it happens, begins to produce small, but detectable variations in the rate at which the engine rotates.
On most modern engines, the crankshaft position sensor also serves to detect misfires, but unlike “normal” misfires that produce large variations in the engines rotational speed, air/fuel imbalances between individual cylinders typically produce variations that are smaller than about 2% of the crankshaft speed. Thus, to distinguish between normal misfires and air/fuel imbalances between cylinders, PCM are programmed to run a very specific monitor after start-up.
As a practical matter, this monitor typically checks for variations in the crankshaft’s rotational speed over two full crankshaft revolutions (one engine cycle), and then compares this information with data received from the upstream air/fuel ratio (or oxygen sensor). If both a variation in the rotational speed of the crankshaft and a deviation from the expected oxygen content in the exhaust gas exist, the PCM will conclude that an air/fuel imbalance between individual cylinders on cylinder bank 1 exists, and it will set code P219A and illuminate a warning light as a result.
Note though that in order to eliminate false positives, the monitor will only run if certain trouble codes are not stored, and that it will only run when certain enabling conditions are met, which are different for different applications. In fact, these enabling conditions are rather precise, such as those for Toyota Venza models, which are given below-
- Air fuel ratio sensor status : Activated
- Engine speed : 1500 RPM or higher, but less than 2300 RPM
- Engine coolant temperature : 167°F or higher
- Atmospheric pressure : 76 kPa (abs) [570 mm Hg (abs)] or higher
- Fuel system status : Closed loop
- Mass air flow : 27.5 gm/sec or more, but less than 40 gm/sec
NOTE: Be aware that the above parameters and values are intended to be purely illustrative, and while they are accurate for Toyota Venza models, proper reference to reliable service information must be made when diagnosing this code on other makes and models.
Where is the P219A sensor located?
The image above shows a leaking exhaust valve (circled), which is a common cause of this code on many applications. Note that while the engine and fuel management systems may be in perfect working order, the loss of compression pressure caused by a damaged valve will cause poor combustion, and therefore, a cyclical variation in the rotational speed of the crankshaft. As a rule of thumb, the PCM will set code P219A if the variation is less than 2% of the crankshafts’ speed; if however, the variation exceeds about 2% of the crankshafts’ speed, the PCM will almost certainly set a misfire code, as opposed to an air/fuel imbalance related code.
What are the common causes of code P219A?
Some common causes of code P219A could include one or more of the following-
- Faulty or defective fuel injector(s)
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors in the fuel injection and/or ignition systems
- Defective or worn spark plug(s)
- Defective or failing ignition coil(s)
- Exhaust leaks
- Defective or worn upstream (located before the catalytic converter) oxygen or air/fuel ratio sensor
- Loss of compression pressure for any reason
- Engine vacuum leak(s)
- Excessive fuel pressure, but note that this condition is more likely to affect all the cylinders equally
- Failed or filing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is replaced
NOTE: Code P219A is common on 2012 – 2014 Toyota Corolla and 2012 -2013 Matrix models as the result of defective exhaust valves. See Toyota Technical Service Bulletin (TSB 0107-14) for details on diagnostic and repair information.
What are the symptoms of code P219A?
Typical symptoms of code P219A could include one or more of the following-
- Stored trouble code and illuminated warning light
- Multiple misfire related codes may also be present in some cases
- Poor fuel economy
- Varying degrees of power loss may occur at some points in the engine’s operating range
- Idling may be rough or erratic
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