A wheel loader with an electronic hydrostatic transmission was throwing a "Throttle Sensor Calibration Out of Range" code. The mechanic replaced the pedal sensor on the floor, but the code returned immediately. The transmission would "hitch" or "slip" when the operator accelerated hard.
We looked at the data stream. The pedal sensor was sending a smooth 0-5 volt signal. However, the transmission ECU compares this signal to an engine speed signal. The problem was a dirty or "drifting" engine speed sensor on the engine crankshaft.
The transmission controller uses a logic map: "If the throttle is 50%, the engine speed should be roughly 2,000 RPM." Because the speed sensor was reading erratically (reading 1,900 RPM when it should have read 2,200 RPM), the ECU assumed the throttle sensor was lying. It went into "limp mode," restricting hydraulic flow to protect the engine from what it thought was an over-fueling condition. Cleaning the rusty reluctor ring on the engine flywheel and replacing the speed sensor fixed the throttle code without touching the pedal.
