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Hi, Welcome to Just Answer, I am Clayton. I can help you with this.
When this occurs, does the tach and the speedo also fall to zero, also what is the voltage reading on the dash during the occurance?
i have a heavy duty otc code reader but it says there is no code. if i flash the codes withe the cruise switch how do i do it? it will take me 15 minutes or so to get to the shop and back
Hi. Sorry for the delay. I will try and help you out.
First I would like to ask you a few questions if that is OK.
Could you get me your engine serial number?
Under what conditions does this happen?
When it is first started? When the truck is parked? Driving down the road?
Do you have any PTO switches or a remote throttle on the truck?
Thanks for the information.
That sound likely a very likely item that can cause your problem.
If the truck has a remote throttle, while hitting a bump or even when it was sitting in your shop could cause this problem. It sounds like the engine is going in and out of what is called PTO mode. Since it is going to and from 1200 RPM's, 1200 RPM's may be a programmed limit.
Do you have a tool at your shop that can read the "Status" of the parameters?
If so, you will be able to see if this is the problem.
There are 2 options.
The first would be to have someone with Cat ET software to go into the ECM and re program the PTO parameter.
The other way would be to locate the wires and switch that activate the PTO. You can trace these wires back to the ECM and remove them. This way the ECM will not get a signal to activate the PTO.