DTC P0266 Cylinder 2 Balance System. GMC Truck GMC C-Series Medium Duty Truck B7 1998

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 6.5L (L65) 🢒 DTC P0266 Cylinder 2 Balance System

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 define limits, this DTC will set. This DTC only monitors fuel reduction.

Conditions for Setting the DTC

•	Engine at idle greater than a total of 90 seconds.

•	All engine misfire DTCs ran and passed.

•	Engine coolant at normal temperatures.

•	Cylinder fault must be constant.

•	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 stores in the Failure Records.

Conditions for Clearing the MIL/DTC

•	A History DTC will clear when forty consecutive warm-up cycles that the diagnostic does not fail (coolant temperature has risen 5°C (40°F) from start up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle.

•	Use of a Scan tool

Diagnostic Aids

Injector balance test on scan tool should be used to confirm fault cylinder problems. Scan tool will cutout specific cylinder requested. It is possible that if a cylinder balance fault has been detected and 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 which 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.

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).

Step

Action

Value(s)

Yes

Important: Before clearing any DTCs, use the scan tool Capture Info to save freeze frame and failure records for reference, as the scan tool loses data when using the Clear Info function.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Scan tool connected.
Start and idle engine.
Engine at operating temperature.
Make sure all DTCs are cleared.
Using the Scan Tool, cutout (Inj. Balance) the suspected cylinder.

Is there an RPM drop in the suspected cylinder?

Go to Step 3

Go to Step 4

DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs were stored refer to the applicable DTC table(s) first.

Are any additional DTCs stored?

Go to the Applicable DTC Table

Go to Diagnostic Aids

Check for the following basic engine mechanical or fuel delivery problems in that cylinder.

•	Injection nozzle malfunctioning refer to Injection Nozzle(s) Diagnosis .

•	Intake manifold restriction.

If a problem is found, repair the problem as necessary.

Was a repair performed?

Go to Step 6

Go to Step 5

Important: The new injectio pump must be timed. Refer to Fuel Injection Pump Timing Adjustment .

Replace the fuel injection pump. Refer to Fuel Injection Pump Replacement .

Is the action complete?

Go to Step 6

Using the scan tool, clear the DTCs.
Start engine and idle at normal operating temperature.
Select DTC, Specific, then enter the DTC number which was set.
Operate the vehicle, within the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

Go to Step 7

Go to Step 2

Does the scan tool display any additional undiagnosed DTCs?

Go to the Applicable DTC Table

System OK