Throttle Position Sensor B Out Of Self Test Range
Your engine's throttle position sensor B isn't reading correctly during the computer's self-test, like a thermometer that can't calibrate itself properly. The ECU can't verify the sensor is working in the expected range.
The ECU monitors throttle position sensor B voltage during its internal self-test routine to confirm the sensor responds correctly across its full range. When the sensor voltage falls outside expected boundaries during this diagnostic test, the fault is triggered. This typically occurs during startup or key-on self-diagnostics.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| TPS B Voltage During Self-Test | 0.5V to 4.5V (full range sweep) | Below 0.5V or above 4.5V during self-test |
| Sensor Response Rate | Smooth linear transition | Erratic or non-responsive signal |
Code P1229 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, P1229 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.