Control Module Long Term Memory Performance/ Immobilizer Code Words Do Not Match
Your car's security system (immobilizer) can't verify that your key matches the engine computer, like a lock that no longer recognizes its correct key. The long-term memory storing the key code has become corrupted or mismatched.
The ECU stores encrypted immobilizer key codes in non-volatile memory during initial programming. On each startup, it compares the transponder signal from the key against the stored code words. If the comparison fails or memory corruption occurs, the fuel and ignition systems remain disabled as a security measure.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Stored Key Code Match | Transponder ID matches stored memory exactly | Key code does not match or memory checksum fails |
| Long Term Memory Integrity | Memory checksum validates correctly | Checksum error or corrupted data detected |
Code P1626 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, P1626 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.