What does P1621 mean on a Chevy?

P1621. Control Module Long Term Memory Performance. Applies to Silverado, Sierra, Tahoe, Corvette, Camaro.

What causes P1621 on a Chevy?

Internal PCM EEPROM wear after years of write cycles Chronic low battery voltage corrupting long-term memory cells Aftermarket tune with corrupted calibration segment Water intrusion into the PCM case from a missing splash shield

How do I fix P1621 on a Chevy?

Verify battery condition and charging voltage; weak power corrupts PCM memory Reflash the PCM with the latest stock calibration using a Tech2/GDS2 or SPS system Return any aftermarket tune to stock and retest before condemning hardware Replace the PCM only if the code returns immediately after a successful reflash

Code

P1621

Control Module Long Term Memory Performance

Category: Powertrain - Computer and Auxiliary Controls
Severity: Check Engine Light
Applies to: Silverado, Sierra, Tahoe, Corvette, Camaro
Related: No single generic twin. See OBD Codes List

What it means

P1621. Control Module Long Term Memory Performance. This Chevy-enhanced code applies to Silverado, Sierra, Tahoe, Corvette, Camaro.

Findings, check these first

Internal PCM EEPROM wear after years of write cycles
Chronic low battery voltage corrupting long-term memory cells
Aftermarket tune with corrupted calibration segment
Water intrusion into the PCM case from a missing splash shield

Standard procedure

Verify battery condition and charging voltage; weak power corrupts PCM memory
Reflash the PCM with the latest stock calibration using a Tech2/GDS2 or SPS system
Return any aftermarket tune to stock and retest before condemning hardware
Replace the PCM only if the code returns immediately after a successful reflash

Look up another code

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Sources and review

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Last updated 2026-09-13.

Report a correction for P1621. Include your vehicle, the issue and a source if you have one.