Was getting "Reduced Engine power" and jerking so I took it to Advanced to have code read. It showed a 4 year old code and nothing else(throttle sensor position I think) so he cleared the codes and now my car won't start. I'm getting power, ac, radio but my gas gauge isn't working and I have a power steering message on the dash. All codes now read no communication with ECM. I checked all fuses switched the relays I knew were working with the ECM/TCM ones and replaced the battery just in case. Nothing worked. I've heard it could be a bad ground but I wouldn't know how to look or replace it. Just had a mechanic check it out (mobile mechanic) and he noted that when they cleared the codes it could stop the car from adjusting to an old issue. Maybe the car knew to drive correctly and when they cleared the codes it couldn't? I'm not sure but it's driving me absolutely bonkers. So I might be on to something. If he cleared the p0121 code, that meant the ECM value went back to default, correct? So if it was off by that much, would it prevent the car from starting? Is it true that I can unplug the throttle body from the ECM and it'll go into safe mode? If I put a new one in and the computer is defaulted will it start again? Is the sensor fried?