2008 GMC C5500 Topkick Truck. Truck cranks but will not start. Connected scanner checked fuel system.
Codes:
U1096: Lost communications with instrument panel cluster (IPC) control module.
P0622: Generator F-terminal circuit
Area of concern seen on scanner: fuel rail pressure regular command is reading 1539.0 mA (0~1500). Font in “red”
fuel pressure sensor voltage at 0.51 V (0~5). Value font not “red”. Could either of these be the cause as no start?
Base fuel injector fuel rate: key on: -1. While cranking: 39
Fuel filter new 200 miles.
Thanks for your help. I have a lot of old school experience on sb Chevy’s , starting to learn scanners.
1/20/23: Update; Two things to learn from this one. 1) Read each line of the scanner very carefully. If possible, assure that the all gages match the scanner. 2) A real man can admit his mistakes.
I decided to scan the truck one more time. As I was reading each line on the active screen, I noticed that the fuel was at 67gal. Oops, no it was NOT, the scanner was showing me that the tank was at .67gal. My diesel gage was reading 1/8 of a tank. One of them had to be wrong. I put 10 gallons in the tank, primed the fuel filter and the truck started. This was my fault for not being observant. Youcanic couldn’t answer why the truck wouldn’t start because they didn’t have all the information (I didn’t send them a pic of that screen). All codes (4) cleared. thanks youcanic
Thank you for providing detailed information about the issues you’re experiencing with your 2008 GMC C5500 Topkick Truck. I’ll do my best to help you identify possible causes for the cranking but not starting problem-based on the diagnostic trouble codes (DTCs) and scanner data you’ve shared.
- U1096 - Lost communications with instrument panel cluster (IPC) control module:
- This code indicates a communication problem with the IPC control module. While it might not directly cause a no-start issue, it’s essential to address communication problems as they can affect the overall functionality of the vehicle. Ensure that the IPC control module and related wiring are in good condition.
- P0622 - Generator F-terminal circuit:
- This code relates to an issue with the generator’s F-terminal circuit. It may not directly cause a no-start condition, but it’s essential to ensure that the charging system is functioning correctly. Check the generator, its wiring, and connections to ensure proper charging.
The values you’ve provided from the scanner data are also worth considering:
- Fuel rail pressure regulator command reading 1539.0 mA (0~1500):
- This value exceeding the specified range could indicate an issue with the fuel pressure regulation system. It’s possible that the fuel pressure regulator or its control circuit may be malfunctioning, affecting the fuel supply.
- Fuel pressure sensor voltage at 0.51 V (0~5):
- The fuel pressure sensor voltage reading appears to be within the expected range. However, it’s still worth inspecting the sensor and its wiring for any damage or loose connections.
Based on the information provided, here are some possible causes to explore:
- Fuel Supply Issues: Check the fuel system for any clogs, leaks, or restrictions that may be affecting fuel delivery. Ensure that the fuel pump is working correctly.
- Electrical Connections: Inspect all electrical connections, including those related to the IPC control module and generator F-terminal circuit. Ensure they are clean, secure, and free from corrosion.
- Charging System: Address any issues related to the generator and charging system, as they can affect overall vehicle performance.
- Fuel Pressure Regulation: Investigate the fuel pressure regulation system, including the fuel pressure regulator, to ensure it’s functioning as intended.
I hope this information helps you in diagnosing and resolving the issue with your truck. If you have any more details or questions, please feel free to share, and I’ll do my best to assist you further.
Hey brotherr The U1096 and P0622 codes suggest possible communication or voltage regulation issues, but they’re not likely the primary cause of your no-start. The key issue seems to be the fuel system. The fuel rail pressure regular command at 1539 mA (above the normal range) shows the ECM is maxing out efforts to increase rail pressure, possibly due to a failing fuel pressure regulator, a bad high-pressure pump, or a blockage. The fuel pressure sensor voltage at 0.51V suggests either no pressure in the rail or a faulty sensor. Since the injectors are being commanded (rate changes from -1 to 39 while cranking), the problem is likely fuel delivery, not injector operation.
Focus on testing the fuel pressure regulator, the rail pressure sensor, and the high-pressure fuel pump. Also, ensure the lift pump is supplying adequate fuel and that the battery and grounds are solid to avoid electrical miscommunication. For precise diagnostics, use your scanner to monitor live fuel system data while cranking, and consider the YouCanic scanner for its ease of use and accuracy in such troubleshooting.