P0123 Fault Code in 2003 Chevrolet Cavalier: Diagnosis and Solutions
I own a 2003 Chevrolet Cavalier with a 2.2L automatic transmission that has been displaying the P0123 fault code. I've already performed several troubleshooting steps including cleaning the throttle body, replacing the Throttle Position Sensor (TPS) twice (with parts from two different suppliers—each costing $60 to ensure quality), and replacing the TPS-to-ECM wire harness. After clearing the codes using a scan tool, the P0123 code persists when the key is turned on. The dark blue (DKBLU) wire shows 4.5 volts at idle. Symptoms include the check engine light staying on, the vehicle failing to accelerate beyond 20 mph, and subsequent overheating issues. The car was running normally the day before with no warning signs or errors. I'm currently considering a clogged catalytic converter or faulty oxygen sensor as potential causes. However, I'm wondering if there are any other underlying factors I may have missed. Additionally, why would the vehicle suddenly stall without prior warning? Any insights or suggestions on how to properly diagnose and resolve this issue would be greatly appreciated.
Are there any other diagnostic trouble codes present? Any additional symptoms like rough idle or stalling at idle? At idle, is the TPS signal on the dark blue (DKBLU) wire above 3.9V? What is the voltage reading on the gray (GRY) wire—this serves as the reference voltage? You mentioned a 4.5V reading on DKBLU when the key is in the ON position (KOEO). What happens to that voltage if you unplug the TPS sensor and recheck the DKBLU wire?