Throttle Position Sensor In Range But Higher Than Expected
Your throttle position sensor is reading higher than the engine computer expects it to be, even though the signal itself is technically valid. It's like the accelerator pedal is saying you're pressing harder than you actually are.
The ECM monitors the throttle position sensor voltage output and compares it against expected values based on engine load and air intake. When the sensor voltage is higher than the predicted threshold for a given operating condition, the ECM detects a mismatch and triggers this code. The sensor itself may be functioning electrically, but the actual throttle angle reading doesn't correlate with other engine parameters.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| TPS Voltage vs. Predicted Load | 0.4-2.0V correlated with intake airflow | Higher voltage than airflow would justify |
| TPS Consistency Check | Smooth voltage change matching pedal input | Abrupt or erratic voltage spikes |
Code P1128 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1128 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.