P1621

Severity: Low

Control Module Long Term Memory Performance/ Immobilizer Code Words Do Not Match

Last updated: July 2026

System

Powertrain

Subsystem

Computer Output Circuit

Code Type

Manufacturer-specific

What does P1621 mean?

P1621 is a manufacturer-specific powertrain diagnostic trouble code. It is defined as "Control Module Long Term Memory Performance/ Immobilizer Code Words Do Not Match". It falls under the computer output circuit area of the vehicle’s powertrain system, and its exact meaning can vary between manufacturers.

When is P1621 set?

The onboard diagnostic system sets P1621 when it detects a condition matching "control module long term memory performance/ immobilizer code words do not match" in the computer output circuit circuit or system. When the fault is confirmed, the module stores the code and, in most cases, turns on a warning light.

This code is generally minor and often relates to a signal, range or performance condition. It should still be inspected, especially if it returns after clearing.

Common symptoms

Check engine light (MIL) illuminated
Rough running, hesitation or loss of power
Increased fuel consumption
Difficulty starting or stalling

Possible causes

A failing or contaminated sensor in the affected circuit
Wiring, connector or ground problems
Vacuum, intake or exhaust leaks
A worn or failing mechanical component
Occasionally, a fault in the control module itself

What to check first

Scan for all stored and pending codes and note the freeze-frame data
Inspect the wiring and connectors for the affected circuit
Check for related leaks, loose components or obvious damage
Test the relevant sensor and its reference/ground with a meter
Clear the code and retest to see whether it returns

Frequently asked questions

What does the P1621 code mean?

P1621 means "Control Module Long Term Memory Performance/ Immobilizer Code Words Do Not Match". It is a manufacturer-specific powertrain trouble code in the computer output circuit area.

Is it safe to drive with a P1621 code?

This code is usually minor, and short-distance driving is often possible, but you should still have it checked — especially if the warning light stays on or the code returns.

How do I fix a P1621 code?

There is no single fix. Start by confirming the code with a scan tool, then work through the likely causes and checks above — inspecting wiring, connectors and the relevant components before replacing any parts. On your specific make, confirm the diagnosis before repairs.

Can I clear the P1621 code myself?

You can clear the code with an OBD-II scan tool, but if the underlying fault is still present it will usually return. Clearing without repair is only useful to confirm whether the fault is active.

Related codes

P1622

Immobilizer ID Does Not Match

P1623

Immobilizer Code Word/ID Number Write Failure

P1620

SBDS Interactive Codes

P1624

Anti Theft System

Important

This information is provided for general reference only. It is not repair advice and may not apply to every make or model. Manufacturer-specific codes can differ. Always confirm a diagnosis with a scan tool and, where needed, a qualified technician before replacing parts.