ASM Mode Circuit [Perf / Winter / Sport / etc]
Your car's drive mode selector (Sport, Winter, Performance, etc.) isn't communicating properly with the engine computer. It's like pressing a button that the computer doesn't recognize or respond to.
The ECU monitors voltage signals from the ASM (Adaptive/Selectable Mode) selector switch. It expects valid discrete voltage levels corresponding to each mode selection. If the signal is missing, intermittent, or out of expected range, the ECU logs a performance fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| ASM Switch Voltage Signal | 0.5V-4.5V with discrete mode steps | Open circuit, short, or voltage outside expected mode range |
| Signal Response Time | <200ms mode detection | Delayed or no mode confirmation to ECU |
Code P0955 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, P0955 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.