GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 Savana 🢒 DTC 🢒 DTC P0278 Cylinder 6 Balance System

Object Number: 420235 Size: MF

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 Running 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.

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 stores in the Failure Records.

Conditions for Clearing the MIL/DTC
    • The PCM will turn the MIL off after 3 consecutive trips without a fault condition.
    • A history DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
    • The scan tool Clear Info function was used.

Diagnostic Aids

The injector balance test on the scan tool should be used to confirm fault cylinder problems. The scan tool will cutout the specific cylinder requested. If a cylinder balance fault has been detected and the engine has been running for a long time, the PCM may try to increase or decrease fuel in the other cylinders to compensate for a rough idle. This can cause multiple cylinder balance DTCs to set. Malfunctioning nozzles are .the most likely cause of cylinder balance DTCs.

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
    • A restricted fuel filter

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. 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

No

1

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

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

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Connect the scan tool
  2. Start the engine.
  3. Allow the engine to idle until the normal operating temperature is reached.
  4. Make sure all DTCs are cleared.
  5. 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

3

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

Are any additional DTCs stored?

--

Go to the Applicable DTC Table

Go to Diagnostic Aids

4
  1. Check for the following basic engine mechanical or fuel delivery problems in the cylinder.
    2. • An injection nozzle malfunction (refer to Injection Nozzle(s) Diagnosis )
    • An intake manifold restriction.
  2. If a problem is found, repair the problem as necessary.

Did you perform a repair?

--

Go to Step 6

Go to Step 5

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

--

6
  1. Using the scan tool, clear the DTCs.
  2. Start engine.
  3. Allow the engine to idle until the normal operating temperature is reached.
  4. Select DTC and the Specific DTC function.
  5. Enter the DTC number that was set.
  6. 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

7

Does the scan tool display any additional undiagnosed DTCs?

--

Go to the Applicable DTC Table

System OK