DTC P0278 Cylinder 6 Balance System. GMC Truck GMC P42 Commercial Chassis 1998

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 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 in order to provide for a smooth idle operation. If the fuel correction amount exceeds the define limits, DTC P0278 will set.

Conditions for Setting the DTC

•	The engine is at idle.

•	The engine coolant is at the normal temperatures.

•	The cylinder fault must be constant.

•	The fuel correction amount exceeds the limits (internal to the PCM).

•	The conditions were 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 after forty consecutive warm-up cycles during which the diagnostic does not fail (the coolant temperature has risen 5°C (40°F) from the start up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle).

•	Use of a Scan tool will clear the DTC codes.

Diagnostic Aids

The injector balance test on the Scan Tool should be used in order to confirm the cylinder problems. The Scan Tool will cutout the specific cylinder requested. If the original complaint was multiple cylinder balance DTCs and the vehicle has a manual transmission, a dual mass flywheel could be at fault. If a cylinder balance fault has been detected and the engine has been running for a long time, the PCM might try to increase or decrease the fuel in the other cylinders in order to compensate for a rough idle which may cause multiple cylinder balance DTCs to set. The Scan Tool snap shot mode can be used in order to properly identify the suspected cylinder. The most likely cause of cylinder balance DTCs are malfunctioning nozzles or engine mechanical (low compression) problems.

If multiple cylinder balance DTCs are set and no problem is found, check for the following:

•	Pinched or restricted fuel feed lines between the fuel tank and the fuel injection pump

•	Restricted fuel filter

•	Fuel waxing

A fuel system restriction could cause the fuel correction to exceed the limits.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

This step will properly identify a suspected cylinder by looking for an RPM drop (if the RPM drops, this indicates that the cylinder is contributing; if the RPM does not drop, this indicates that the 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

Connect the Scan Tool.
Start the engine.
Allow the engine to idle at the normal operating temperature.
Make sure that all of the DTCs are cleared.
Use the Scan Tool in order to 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 any additional DTCs were stored, refer to the applicable DTC table(s) first.

Are there 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.

•	Low compression refer to Engine Compression Test in Engine Mechanical

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

•	Kinked or bent injection lines

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

Was a repair performed?

Go to Step 6

Go to Step 5

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

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

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