2004 Chevrolet Impala P0122: Throttle Pedal Position Sensor Low Input Issue After Multiple Repairs

The P0122 code typically indicates that the Throttle Position Sensor (TPS) is sending a signal below 0.1 volts to the Powertrain Control Module (PCM). In systems without drive-by-wire, this sensor is usually located on the throttle body. For accurate diagnosis: - With the key ON and engine OFF, backprobe the TPS signal wire (terminal C, dark blue) using a multimeter: it should read between 0.5V and 1.0V at idle. - Disconnect the TPS connector and test terminal A (5V reference): with the key ON and engine OFF, this should register approximately 4.8 volts. If either reading is off or absent, that points to a faulty sensor or missing reference voltage. A scan tool showing live data from both the TPS and Manifold Absolute Pressure (MAP) sensors would be highly valuable for confirming whether the PCM is receiving valid input. Without this, troubleshooting remains challenging.

The catalytic converter did not melt or damage the muffler — we actually removed the muffler to test that theory. The thermostat was replaced because the engine consistently ran too cool and the check engine light indicated a need for replacement. The car performed flawlessly on Wednesday, including an 80-mile commute. However, by Thursday morning, it would not stay running. It seems counterintuitive — as more parts are replaced, the vehicle's performance deteriorates further.

Key ON, engine OFF: Test the TPS signal wire (terminal C, dark blue) with a multimeter. - Positive lead to terminal C, negative lead to battery ground — expect readings between 0.5V and 1.0V at idle. Next, disconnect the TPS connector and test terminal A (5V reference): - Positive lead to terminal A, negative to battery ground — should read approximately 4.8 volts. These tests will help determine if the sensor is functioning correctly or if there's a missing voltage reference.

We completed wiring checks last night and confirmed all connections are intact. The TPS was replaced again to rule out a faulty sensor. The engine now runs rich, but no additional diagnostic codes appear — only the P0122 code remains. This suggests an underlying issue beyond just the throttle position system.

Please provide more details: - Is there a stable 5V reference at the TPS? - Is the ground connection solid? - What is the signal voltage at idle? - Does shaking or tapping the TPS connector affect readings? Also, check if your scan tool displays manufacturer-specific codes (e.g., P1122) and whether it shows freeze frame data. This information will help determine if the issue stems from sensor failure or faulty input to the PCM.

I understand that many of us try to assist, but we're limited by incomplete information. Cold-start stalling is often caused by incorrect fuel-air mixture — either too much air or insufficient fuel. How do you know the engine is running rich? That may explain why the catalytic converter failed. If there's a poor ground, signal voltage will be high (not low), which contradicts P0122. A shorted or open wire, or missing 5V reference, could also cause this issue. A vacuum leak can cause cold-start stalling. Try feathering the throttle to keep the engine running — does it hold? Disconnect the MAP sensor and see if the car runs better. If the PCM is receiving corrupted data from a faulty sensor, a scan tool showing live TPS and MAP readings is essential. Check that the IAC (Idle Air Control) connector is properly plugged in. Confirm 5V reference presence and signal voltage at key-on engine-off state. Please share these details so we can assist further.

Good morning, I confirmed a stable 5-volt reference. All wiring was traced and found to be intact. The root cause turned out to be a failed master cylinder that allowed brake fluid to enter the power booster. This fluid was drawn into the engine intake and burned, causing severe smoke, hot catalytic converter, and multiple engine-related codes. After replacing both the master cylinder and brake booster, the car started and ran smoothly for about 45 minutes. However, when I attempted to drive it in reverse, it stalled again. A fuel pressure test revealed no pressure on the Schrader valve during cranking — indicating a failing fuel pump. We replaced the fuel pump, after which the engine started and ran well for several drives. However, around the fifth start-up cycle, RPMs began surging and the engine shut off unexpectedly. No diagnostic codes appear on the scanner. I'm now seeking help to diagnose this new issue — possibly related to fuel delivery or sensor feedback.

"The car was showing a fuel pressure regulator code. What specific code did you receive? Is your scan tool actively communicating? Does the Check Engine Light (CEL) come on at every start and then go off? If the engine won't start, perform basic checks: 1. Fuel pressure — must be measured with a dedicated fuel pressure gauge. 2. Spark at multiple spark plugs. 3. Injector pulsing activity. Try starting the engine while spraying carburetor or brake cleaner into the throttle body — if it starts and runs briefly, that may indicate a vacuum leak or intake issue. Please let us know if this test results in any response. This could help identify whether the problem lies in fuel delivery or sensor input.