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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 GMC T-Series Medium Duty Truck F6/F7/F8 🢒 DTC 🢒 DTC P1263

Circuit Description

The fuel 1 injector drive circuit is a high-voltage supply and drives injectors installed to cylinders 1, 2, and 3. The engine control module (ECM) steps up the battery voltage and supplies the resulted high voltage to the related injectors continuity. If the fuel 1 injector drive circuit supply to cylinder 1, 2, or 3 is short to ground circuit or if the injector solenoid control circuit 1, 2, or 3 is short to ground, this DTC will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1263 Injector Positive Voltage Control Circuit Group 1 Low Voltage

Conditions for Running the DTC
    • The ignition switch is ON.
    • The battery voltage is between 10-16 volts.
    • The engine is running.
    • The crankshaft position (CKP) sensor is not failed.

Conditions for Setting the DTC

The ECM detects that the injector power supply circuit is short to ground circuit.

Action Taken When the DTC Sets
    • The ECM illuminates the malfunction indicator lamp (MIL) and reduced engine power indicator lamp, if fitted, when the diagnostic runs and fails.
    • The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.
    • The ECM disables 1, 2, and 3 injector operation.
    • The ECM limits fuel injection quantity for fail-safe operation.
    • The ECM closes the exhaust gas recirculation (EGR) valve and holds to close position.
    • The ECM limits fuel rail pressure for fail-safe operation.
    • The ECM limits acceleration operation range.
    • The ECM inhibits the PTO control.
    • The ECM inhibits cruise control.

Conditions for Clearing the DTC
    • The MIL resets when the ignition is turned OFF.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • Clear the MIL and the DTC with a scan tool.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Observe the Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Failure Records.

Does the DTC fail this ignition?

--

Go to Step 3

Go to Intermittent Conditions

3
  1. Turn OFF the ignition.
  2. Disconnect the injector harness inline connector from the cylinder head cover case.
  3. Measure the resistance through the intermediate connector between the injector power supply circuits and the 1, 2, and 3 injector control circuits.

Are the all resistance measures less than specified value?

2 ohms

Go to Step 4

Go to Step 6

4
  1. Turn OFF the ignition.
  2. Disconnect the injector harness inline connector from the cylinder head cover case.
  3. Measure the resistance through the intermediate connector between the injector power supply circuits and a known good ground.

Are the resistance measures more than the specified value?

10Mohms

Go to Step 5

Go to Step 6

5
  1. Test the injector power supply circuits between the engine control module (ECM) and the inline connector for a short to ground circuit.
  2. Repair the circuit, as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

6
  1. Remove the cylinder head cover.
  2. Inspect the upper portion of the appropriate injector and injector harness.
  3. Repair the condition, as necessary. Refer to Cylinder Head Replacement .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 7

7
  1. Test the injector power supply circuits between the injector terminals and the intermediate connector for the following conditions:
    2. • A short to ground circuit
    • A short to injector control circuit
  2. Repair the circuits, as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Disconnect the injector terminals from the injectors.
  3. Measure the resistance of 1, 2, and 3 injector solenoid coil.

Are all resistance measures less than specified value?

2 ohms

Go to Step 9

Go to Step 11

9
  1. Turn OFF the ignition.
  2. Inspect for connections at the intermediate connector.
  3. Repair the connections, as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Intermittent Conditions

10
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Inspect for poor connections at the harness connector of the ECM.
  4. Repair the connections, as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Replace the appropriate injector. Refer to Fuel Injector Replacement and Fuel Injector Flow Rate Programming .

Did you complete the replacement?

--

Go to Step 13

--

12

Important: The replacement ECM must be programmed.

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data , and Fuel Injector Flow Rate Programming .

Did you replacement?

--

Go to Step 13

--

13
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 14

14

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK