Yale 656-5 – Engine Control Unit (ECU) / Vehicle System Controller: GM Gas Drive Injector 6 Open Circuit

The electrical circuit controlling fuel injector #6 is incomplete or broken. This is typically caused by a fuel injector open circuit, an injector driver module failure, or a functional failure within the controller.

• Yale and Hyster Forklifts
• Yale VX series
• Hyster FT series (e.g., 40FT-120FT)
• Forklifts equipped with the GM 4.3L V6 Gas/LPG engine

1. 1

   Visual Inspection: Check the electrical connector at fuel injector #6 to ensure it is fully seated, clean, and free of corrosion or damaged pins.

2. 2

   Resistance Test: Disconnect the injector and measure the resistance across its pins with a multimeter. Typical GM injectors should read around 10–16 ohms. If the reading is infinite (open) or zero (shorted), the injector itself has failed.

3. 3

   Voltage Check: With the key in the ON position, check for 12V at the injector connector's power pin (injectors receive battery power through the ECU relay).

4. 4

   Continuity Test: Check the wiring harness for continuity between the ground/control side of the injector connector and the ECU to rule out a broken wire in the harness.

5. 5

   Injector Pulse Test (Advanced): If using a diagnostic service tool (DST), run the engine at ~1000 RPM and use the 'Injector Kill' mode to disable injector 6. If disabling it causes no RPM drop, the circuit or injector is completely dead.

1. 1

   Turn off the forklift, lower the forks, and disconnect the battery to prevent electrical shorts.

2. 2

   Gain access to the engine bay and locate fuel injector #6 on the GM 4.3L engine fuel rail/manifold.

3. 3

   Disconnect the electrical harness from the injector.

4. 4

   If the injector failed the resistance test: Relieve the fuel system pressure, remove the retaining clips/fuel rail, and extract the faulty injector.

   Lubricate the O-rings on the new injector and install it into the manifold/rail.

5. 5

   If the wiring harness failed the continuity test: Locate the break or chafe in the wiring harness between the injector and the ECU.

   Splice and repair the wire using proper heat-shrink connectors.

6. 6

   If both the injector and wiring are good: The ECU's internal injector driver has failed.

   The ECU will need to be replaced or sent out for repair/reprogramming.

7. 7

   Reconnect the electrical harness, reinstall any removed components, and reconnect the battery.

8. 8

   Start the engine, check for fuel leaks, and verify that the 656-5 fault code has cleared and the engine no longer misfires.