DTC P1264. GMC Truck TopKick C-Series (Conventional) C6/C7/C8 2005

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Conventional) C6/C7/C8 🢒 Engine 🢒 Engine Controls - 7.8L 🢒 DTC P1264

Circuit Description

The fuel 1 injector drive circuit is a high-voltage supply and drives injectors installed to cylinder 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 the cylinder 1, 2, or 3 is short to voltage circuit or if the injector solenoid control circuit 1, 2, or 3 is shorted to voltage, this DTC will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1264 Injector Positive Voltage Control Circuit Group 1 High Voltage

Conditions for Running the DTC

•	The ignition 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 voltage 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 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	Observe the Failure Records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. 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	Turn OFF the ignition. Disconnect the injector harness inline connector from the cylinder head cover case. Measure the voltage through the inline connector between the injector power supply circuits and a known good ground. Turn ON the ignition, with the engine OFF. Are the voltage measures more than the specified value?	1 V	Go to Step 4	Go to Step 6
4	Turn OFF the ignition. Disconnect the engine control module (ECM) and the injector connector. Inspect for poor connections at the harness connector of the ECM and the injector. Repair the connections, as necessary. Did you find and correct the condition?	--	Go to Step 7	Go to Step 5
5	Test the injector power supply circuits between the ECM and the inline connector for a short to voltage circuit. Repair the circuits, as necessary. Did you find and correct the condition?	--	Go to Step 7	Go to Diagnostic Aids
6	Important: The replacement ECM must be programmed. Replace the ECM. Refer to Engine Control Module Programming and Setup , Engine Control Module Replacement/Restore Fuel Rate Data , and Fuel Injector Flow Rate Programming . Did you complete the replacement?	--	Go to Step 7	--
7	Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. 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 8
8	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