Diagnosing automotive sensor issues can be complex, but a systematic approach, combined with shared knowledge from experienced technicians, can guide you to effective solutions. This case study examines a user’s experience resolving discrepancies between Throttle Position Sensor (TPS) and Accelerator Pedal Position (APP) sensor readings, a problem often flagged by OBD2 systems and potentially related to a “Tp_b Obd2” error.
Initially, seeking advice from a seasoned GM technician, the user was directed to investigate circuit wiring, connections, and APP sensor resistance before considering parts replacement. Reflashing the ECM/PCM was also suggested as a potential remedy. This expert insight underscores the importance of thorough diagnostics before jumping to conclusions.
However, proceeding with intuition, the user decided to replace the APP sensor. To understand the rationale, let’s analyze the sensor readings provided before and after the replacement.
Prior to replacing the APP sensor, readings from APP sensors #1 and #2 were recorded, revealing significant differences even when the pedal was undepressed:
| APP #1 | APP #2 |
|---|---|
| 17.3 (undepressed) | 9.4 (undepressed) |
| 28.6 | 13.7 |
| 32.9 | 15.3 |
These initial readings indicated a clear inconsistency between the two APP sensors. APP sensor #2 consistently registered lower values than APP #1 across different pedal positions.
Alt text: Table showing initial Accelerator Pedal Position (APP) sensor readings with APP #1 and APP #2 values, highlighting discrepancies in undepressed and depressed states for OBD2 troubleshooting.
After installing a new APP sensor, the user conducted a comparative analysis. Focusing on APP sensor #2, the lower reading sensor, they manually adjusted the pedal to match the previous APP #2 readings. The subsequent readings are shown below:
| APP #1 | APP #2 |
|---|---|
| 20.4 (undepressed) | 9.4 (undepressed) |
| 28.2 | 13.7 |
| 31.4 | 15.3 |
Even without pedal depression, a notable difference is evident in the undepressed values post-replacement. It’s important to note that while percentage values for APP sensors may vary as APP #2 acts as a backup, TPS sensors should ideally exhibit closer readings.
Examining the TPS readings revealed a substantial disparity. TPS #1 registered 31.0%, while TPS #2 showed 39.8%. This significant divergence prompted a similar comparative test as performed with the APP sensors. The pedal was manipulated until TPS #1 reached 31.0%, at which point TPS #2 reading aligned closely around 31%.
Alt text: Image displaying Throttle Position Sensor (TPS) readings before repair, illustrating a notable difference between TPS #1 and TPS #2 percentages for OBD2 diagnostics.
This observation led to a hypothesis regarding the vehicle’s electrical system. The user speculated that TPS #1 and APP #1 might share a common 5V reference circuit, and similarly, TPS #2 and APP #2 might share another 5V reference circuit.
Based on these readings and the potential shared reference circuit, the decision to replace the APP sensor first was made. The user theorized a possible internal short within the original APP sensor affecting both APP and TPS readings due to the shared circuits.
Alt text: Screenshot of Throttle Position Sensor (TPS) values after adjustment, demonstrating improved alignment between TPS #1 and TPS #2 post APP sensor replacement in an OBD2 system.
While the user acknowledges a non-professional mechanic background, this DIY approach highlights a logical diagnostic process. By observing sensor reading discrepancies and understanding potential circuit relationships, a likely faulty APP sensor was identified and replaced. The user also expressed hope that this repair might resolve a P0420 code, related to catalytic converter efficiency, suggesting a possible indirect link between sensor issues and emissions control systems.
This real-world example underscores the value of sensor data analysis in OBD2 diagnostics and the importance of considering circuit interactions when troubleshooting sensor-related problems, especially when dealing with potential “tp_b obd2” errors or similar sensor reading inconsistencies. Further investigation and professional verification are always recommended for complex automotive issues.
