Theory Of Operation
The purpose of the Cylinder Imbalance Detection diagnostic monitor is to detect an air/fuel ratio imbalance between the cylinders across an entire cylinder bank.
Although the DTC description does not indicate as such, this fault will set because a specific cylinder on this bank is out of balance with the other cylinders. The fault may not be easily noticeable to the technician. During diagnosis, it is necessary to pay close attention to small differences between the cylinders during each of the test steps.
This imbalance can be caused by a number of different malfunctions including but not limited to:
- Exhaust Manifold to Cylinder Head leak at a specific cylinder.
- Intake Manifold leak at a specific cylinder.
- Fuel Injector problem.
- Variable cam lift failure.
- Camshaft/ Valvetrain problems.
- Ignition system problems at a specific cylinder.
- Engine mechanical problems relating to cylinder combustion at a specific cylinder.
The Cylinder Imbalance Detection requires that the Upstream Oxygen (O2) Sensors are capable of operating at high frequencies, since an aged O2 Sensors response capability at a higher frequency range can be degraded. Therefore, before this monitor can become active, the O2 Sensor High Frequency Response monitor is performed to see if the sensor is even capable of detecting an imbalance.
Once active, the Cylinder Imbalance Detection monitor matches up the Upstream O2 Sensor signal with the corresponding cylinders on that bank. Each cylinder is monitored and adjustments are made as needed for each cylinder to correct an air/fuel ratio imbalance. If an individual cylinder reaches a calibrated adaptation threshold (15%), the diagnostic monitor will be considered failing.