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OEM ECU Open loop fault

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what is the definition or meaning of an open loop fault ??

What in the ECU , wiring harness , sensors can cause the ECU to go into open loop fault ??

The more detailed your comments are the better for those of us that do not understand, what this is . Thanks Terry

I think it would be helpful to know what ECU you are working with. But a quick Google search found this as the first hit:

Open Loop - Fault is when both upstream oxygen or A/F sensors on a two bank vehicle have a fault. This could be caused by two bad upstream O2 sensors or both banks can be extremely rich or extremely lean. On a single bank vehicle Open - Loop Fault occurs when the upstream sensor has a fault. This could be caused by a bad upstream sensor or the vehicle is extremely rich or extremely lean

that came from here:https://www.iatn.net/forums/13/42000/seeing-the-whole-picture-the-importance-of-loop-status

Ok thanks . My ECU is a 1997 Ford EEC V

The Tuning School recently did a video on open loop fault . But there issue was a large cam . That was causing high miss fire counters. That triggered an open loop fault . Are these the only 2 items that can cause open loop fault ?? Or are there other causes of open loop fault ?

The Tuning school was working on a Gen 3 GM ECU

When the OBD system judges that a sensor has failed, it will ignore that sensor's reading and rely on a model'd value or a fixed failsafe value. So for example if the MAP sensor fails, the ECU can calculate the manifold pressure based on the throttle position and rpm. If the O2 sensor fails, but it will disable that sensor and use a look up table of what kind of fueling to supply.

That's a general description. In that case of misfire "open loop fault," the misfire monitor is designed to work on a stock engine. It looks at the acceleration of the crank angle sensor signal basically. With a cam the valvetrain changes, the combustion is more unstable, etc. So it's tripping the misfire monitor. There are two solutions: recalibrate the misfire monitor (which is not normally an option in the aftermarket) or turn it off and disable the code.