For 1990-2009 cars

# Powertrain Control Module (PCM), Engine Control Module (ECM), Transmission Control Module (ECM), Transmission Control Module (TCM) DTCs P0601/P0602/P0603/P0604,/P1621 Shared in Multiple Modules

Subject: | Powertrain Control Module (PCM), Engine Control Module (ECM), Transmission Control Module (TCM) Diagnostic Trouble Code(s) (DTC)(s) P0601, P0602, P0603, P0604, P1621 Shared In Multiple Modules

Models: | 2005-2006 GM Passenger Cars and Light Duty Trucks (including Saturn)

| 2005-2006 HUMMER H2

| 2006 HUMMER H3

| 2005-2006 Saab 9-7X

Beginning in 2005, some control modules (ECM's, TCM's) have specific codes that describe internal failures of the module. These DTCs are not module specific and can be found on any controller that has these codes.

Society of Automotive Engineers (SAE) J2012 committee has set these specific codes to be an industry standard of all manufacturers.

Currently, these common codes are:

• | P0601 -- Control Module Read Only Memory (ROM)

• | P0601 -- Transmission Control Module (TCM) Read Only Memory (ROM)

• | P0602 -- Control Module Not Programmed

• | P0602 -- Transmission Control Module (TCM) Not Programmed

• | P0603 -- Control Module Long Term Memory Reset

• | P0603 -- Transmission Control Module (TCM) Long Term Memory Reset

• | P0604 -- Control Module Random Access Memory (RAM)

• | P0604 -- Transmission Control Module (TCM) Random Access Memory (RAM)

• | P1621 -- Control Module Long Term Memory Performance

• | P1621 -- Transmission Control Module (TCM) Long Term Memory Performance

Important:

• | Use caution when diagnosing these shared codes to perform the appropriate diagnostic procedure on the appropriate module.

• | A low voltage condition may set one or more of the above codes. Repair any low voltage conditions prior to diagnosing the above codes.

Refer to the appropriate Service Information (SI) document for Diagnosis and Repair procedures.