1998 Saturn SL2 P0122 Fault: Throttle Position Sensor Voltage Issue and Gray Wire Diagnosis
After replacing the throttle position sensor (TPS) on my 1998 Saturn SL2, I reset the engine control module and retested the vehicle. The P0122 code reappeared. I measured the voltage at the TPS: approximately 0.27V when the throttle is closed, which aligns with the Haynes Auto Repair Manual's specifications for that position. When the throttle is fully open, the reading is around 2.66V. According to the manual, it should read about 4.0V under full throttle conditions. I also tested the gray wire connected to the TPS sensor and could not obtain a stable voltage reading. This suggests a potential issue with either the wiring or the sensor itself. Given that the P0122 code relates to an incorrect throttle position signal, I'm concerned about whether this is due to a faulty sensor, a broken wire, or a grounding problem. Any insights or troubleshooting steps for this specific 1998 Saturn SL2 P0122 issue would be greatly appreciated.
The gray wire on the TPS provides a 5-volt reference signal from the Powertrain Control Module (PCM). If you don't measure 5 volts directly at the PCM end of that wire, check the connection there first. If 5V is present at the PCM, then the issue may be a broken wire between the PCM and the sensor. If no voltage is detected at the PCM, it indicates a potential fault in the PCM itself. Additionally, ensure the black ground wire is properly connected and providing a solid ground—this is essential for accurate TPS signal reading.