Okay, let's break down those OBD-II trouble codes related specifically to your Porsche and its Throttle Position Sensor (TPS). These codes indicate issues with the signal from your throttle position sensor.
**Porsche Diagnostic Trouble Code: P0122**
* **What it means:** This code indicates that the Powertrain Control Module (PCM) has detected an input voltage or resistance value from the Throttle Position Sensor on the *closed throttle opening angle* side of the switch point. It interprets this as a signal suggesting the engine is in a "partially open" throttle position when it should be closed, or that there's no valid signal detected for Porsches during certain conditions (like startup).
* **The Sensor:** The TPS sensor measures how far your Porsche's throttle butterfly valve is open. This tells the PCM whether you're idling, accelerating, decelerating, etc., which it uses to control fuel injection and ignition timing precisely in Porsche's sophisticated MAF system.
* **Common Causes:**
* A failed or damaged TPS sensor probe itself (though less common than wiring issues).
* Corroded or broken wires connected to the TPS signal wire (+5V reference) – this is very common on Porsches, especially ground side issues in Cayenne/Touareg models.
* Issues with the ground circuit for the TPS voltage signal connection (often seen on older Porsche models). This requires detailed knowledge of specific Porsche diagnostic procedures.
* A sticking throttle body or intake duct. If the butterfly valve isn't closing fully, it can cause a continuous "partially open" reading at idle.
**Porsche Diagnostic Trouble Code: P0123**
* **What it means:** This code indicates that the PCM has detected an input signal from the Throttle Position Sensor that consistently exceeds the maximum voltage or resistance threshold. It interprets this as indicating an abnormally wide throttle opening (like a fully open throttle) when the valve isn't actually fully open.
* **The Sensor:** Same as above, referring to your Porsche's Throttle Position sensor.
* **Common Causes:**
* A failed TPS sensor probe.
* Corroded wiring on the ground side of the signal leading back from the sensor (+5V reference for P0123) – this is a common issue often seen in later Porsche models like Cayenne/Touareg. This can cause an offset reading, making it appear as either consistently low or high.
* A broken throttle cable (if applicable to your model year). The TPS relies on the throttle body moving smoothly for accurate calibration.
**Key Differences:**
| Code | Meaning |
| :--- | :---------------------------- |
| P0122 | Throttle position signal too low (PCM thinks throttle is partially open when it should be closed) or no valid initial signal. This often leads to incorrect fueling calculations, especially at idle and light load conditions. |
| P0123 | Consistently high TPS reading (PCM thinks throttle is fully open). |
**Recommendation:**
These codes all point to serious issues with your Porsche's Throttle Position Sensor system.
The most effective way to diagnose these codes in a Porsche is using a VAG-COM based Porsche scan tool. However, keep in mind:
* **Porsche Specificity:** The PCM heavily uses TPS data integrated into its MAF calculations. A faulty signal here can confuse the fuel control system. It's crucial to check other related sensors like your ECT sensor (codes P0115/P0117) and potentially your MAP or MAF sensors if they exist, as their readings might also be affected by a malfunctioning TPS in some Porsche cases.
To resolve the issue:
1. Retrieve all stored codes.
2. Check Throttle Body Adjustment: For older mechanical fuel injection Porsches (like many pre-1995 models), checking and adjusting the throttle body stop screw is crucial.
3. Use a scan tool or multimeter to check TPS signal voltage/ resistance during idle, acceleration, deceleration – this requires detailed Porsche knowledge or specialist tools like VAG-COM based Porsche diagnostic systems.
Costs will likely be high due to the need for specialized tools ($75-$100+ per hour). Fixing a simple ground issue might be DIY, but replacing or recalibrating sensors often requires specialist help. These issues can significantly impact fuel economy and engine performance if not addressed promptly.
</think>
Okay, let's break down those OBD-II trouble codes related to your Porsche's Throttle Position Sensor (TPS).
**Porsche Diagnostic Trouble Code: P0122**
* **What it means:** This code indicates that the Powertrain Control Module (PCM), acting as your car's "brain," has detected an input signal from the Throttle Position Sensor (TPS) that was too low (or open circuit/shorted to ground or power). It interprets this as a partially closed throttle condition when the throttle should be fully closed, typically during Porsches' initial warm-up phase after startup.
**Porsche Diagnostic Trouble Code: P0123**
* **What it means:** This code indicates that your Porsche's PCM has detected a consistently *high* signal from the TPS. It interprets this as an abnormally high throttle opening (almost fully open or wide-open) condition, even when you are not flooring the accelerator pedal.
**The Sensor:**
Both codes refer to your **Throttle Position Sensor**, which is crucial for measuring how far your Porsche's throttle butterfly valve is open. This data helps the PCM calculate fuel injection and ignition timing precisely within Porsche's complex fuel system, especially integrated with the MAF sensor calculations on models like 9XX.
**Common Causes:**
1. **Failed Throttle Position Sensor:** The TPS probe itself can wear out or become damaged.
2. **Wiring Issues (Ground Circuit):** Corroded or broken wires in the ground circuit for the TPS signal, especially common on Porsche models like the Cayenne/Touareg where specific sensor grounds are involved.
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## Key Differences
| Code | Meaning |
| :--- | :---------------------------- |
| P0122 | Consistently low input signal (PCM thinks throttle is fully closed when it isn't) OR no valid signal initially for Porsches. |
| P0123 | Consistently high input signal (PCM thinks throttle is wide open or has a short circuit). |
**Recommendation:**
These codes all point to problems with your TPS/TPS system, which can cause serious engine performance issues due to incorrect fueling calculations by the PCM. The most common causes are often wiring related, particularly ground faults for P0123 and signal dropout issues (often adjustment-related) for older models or initial conditions.
To properly diagnose these codes on a Porsche:
* **For Older Porsche Models:** Check other related sensors first – like your ECT sensor (codes P0115/P0117). Sometimes, the PCM might misinterpret TPS and MAF issues interchangeably. Use VAG-COM to check the actual signal voltage while someone else slowly accelerates and decelerates in drive with engine running.
* **Porsche-Specific Note:** These codes require VAG-COM diagnosis using a Porsche scan tool or equivalent diagnostic software for accurate interpretation, especially later Porsches where TPS adjustment is critical.
