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  • Writer's pictureBlue Chip Diesel

We should discuss the CCD bus

You've done the hotwire test. Your truck runs but you are still having problems. This could be an issue prior to the injection pump. It can be either the ECM or lack of rpm signal from the crank shaft position sensor in early truck and/or CAM shaft position sensor in all trucks.

If these sensors function, there may be a problem with what is called the 'CCD bus.' This is a common information two-wire system that allows various components of the truck to monitor certain functions, such as RPM.

If this system is shorted-out by a failed component, it can bring down the whole CCD bus system and prevent the truck from starting. One tool we have found in diagnosing this is to unplug the center plug of the PCM, located on the firewall usually the center gray plug. If the truck starts with the PCM unplugged and/or the center plug unplugged, that's an indicator of a problem with the bus and may involve testing of many wires and using a schematic to trace where the problem may be.

It can be difficult, so we wish you luck, but if you get into a pickle give us a call!

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