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Caterpillar GC40 LP truck wont accelerate after a hot restart. Has fault code 2121 which is for the throttle pedal sensor I think. Can you tell me exactly what code 2121 means and what will fix this forklift. Does not happen all the time, just every few days after hot restart the throttle has no response and the truck wont go.

Fault code 2121 is TPPS1 (throttle pedal position sensor) out of range on the GC40. The throttle POT 1 and 2 have to be within 20% of each other. Both sensors are inside the throttle POT assembly. You can view the actual percentage using your laptop software. Here is a picture of the diagnostic connector location. It is usually clipped just under the fuse / relay box. That sensor is most likely the cause of your problem. There is a possibility that you did not get it adjusted properly when you replaced it. You must look at live data to set the sensor. The specification for the Cat5erpillar GC40 with the Vortec 4.3L V6 says it must be at least .2 Volts. When i replace them, i always set them to .650 volts. This seems to be the best value and have never had a problem with it.

Just loosen the 2 mounting screws and turn the POT slowly while watching the voltage value. Once you are right around that number, tighten the screws and make sure the value stays. Sometimes it will change while tightening it down. If you do not have a laptop with software to view the data, you can just use an volt meter on the sensor output wire to watch the voltage change when you adjust it.

Just for reference for anyone who is not sure where the TPPS sensor is, here is picture with the floor board removed. It is located on the throttle pedal linkage.