DTC P0278 Cylinder 6 Balance System. GMC Truck GMC K Pickup

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2000 🢒 GMC K Pickup - 4WD 🢒 DTC 🢒 DTC P0278 Cylinder 6 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 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 will clear after 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. 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

The numbers below refer to the step numbers 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

Values

Yes

Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and failure records for reference. The control modules data is deleted once the Clear Info function is used.

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

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

The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs were stored refer to the applicable DTC tables first.

Are any additional DTCs stored?

Go to applicable DTC

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 problem found?

Go to Step 6

Go to Step 5

Important: The new injection 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 the engine.
Allow the engine to idle at normal operating temperature.
Select DTC and the Specific DTC function.
Enter the DTC number which was set.
Operate the vehicle, with the Condition 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 applicable DTC

System OK