Possible causes
– Faulty Powertrain Control Modules (PCM)
– Low car battery voltage
– 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 GMC 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.
GMC Technical Service Bulletins for P1621 code
2008 GMC SIERRA POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)
2008 GMC SIERRA DENALI POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)
2008 GMC YUKON POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)
2008 GMC YUKON DENALI POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)
2008 GMC YUKON DENALI XL POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)
2008 GMC YUKON XL POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)
2010 GMC TERRAIN POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)
2007 GMC ACADIA POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)
2008 GMC ACADIA POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)
2009 GMC ACADIA POWER TRAIN:AUTOMATIC TRANSMISSION:CONTROL MODULE (TCM, PCM)