GM/Detroit 6.5L ENGINE CONTROLS – DTC P0266 Cylinder 2 Balance System

Refer to Fuel Injection Line Routing Figure.

Circuit Description
The PCM has the ability to increase and decrease the amount of fuel to each cylinder to provide smooth idle operation. If the PCM decides that the fuel reduction amount to a specific cylinder exceeds defined limits, this DTC will set. This DTC only monitors fuel reduction.

Conditions for Running the DTC
• Engine at idle more than a total of 90 seconds.
• All engine misfire DTCs ran and passed.
• Engine coolant at normal temperatures.
• Cylinder fault must be constant.

Conditions for Setting the DTC
• Amount of fuel reduction for a specific cylinder exceeds limits (internal to PCM).
• Conditions met for 2 seconds.

Action Taken When the DTC Sets
• The PCM will not illuminate the malfunction indicator lamp (MIL).
• The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Failure Records.

Conditions for Clearing the MIL/DTC
• A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
• The use of a scan tool.

Diagnostic Aids
Injector balance test on scan tool should be used to confirm fault cylinder problems. The scan tool will cut out the specific cylinder requested. It is possible that if a cylinder balance fault has been detected and the engine has been running for a long time, the PCM will try to increase or decrease fuel in other cylinders to compensate for a rough idle. This can cause multiple cylinder balance DTCs to set. The scan tool snap shot mode can be used to properly identify the suspected cylinder. The most likely cause of cylinder balance DTCs are malfunctioning nozzles.

If multiple cylinder balance DTCs are set and no problem is found, check for the following:
• Pinched or restricted fuel feed lines between fuel tank and fuel injection pump
• Restricted fuel filter

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
2. This step will properly identify a suspected cylinder by looking for a RPM drop (if RPM drops, cylinder is contributing, if not cylinder is not contributing).

 

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