Possible causes

– Faulty Powertrain Control Modules (PCM)
– Low car battery voltage

When is the code detected?

If the checksum of the Electronically Erasable Programmable Read Only Memory (EEPROM) does not match a predetermined value by the Powertrain Control Modules (PCM), DTC P1621 will set.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1621 CADILLAC Description

The Powertrain Control Modules (PCM) Electronically Erasable Programmable Read Only Memory (EEPROM) contains data essential to running the engine and transmission. The PCM stores critical preprogrammed data within the EEPROM, this data remains even if the vehicles’ battery is disconnected. At power up the PCM checks the integrity of this data.