The Consequences of Swapping Control Modules

GM diagnostic strategy does not support the practice of swapping control modules during the course of diagnosis or in order to expedite a repair.

 

Features in today's vehicles are increasingly software-configurable. They can affect vehicle safety systems, anti-theft systems, performance, and customer personalization information. Many current vehicles have one or more control modules that cannot be swapped. Additionally, models using the Global A electrical architecture (2010 Camaro, LaCrosse, Equinox, Terrain and SRX) will exhibit a variety of fault symptoms when certain control modules are swapped between vehicles. Swapping these security-related modules will cause difficult and time-consuming remediation processes that may include the purchase of new components for both vehicles.

 

On Global A models, some modules that traditionally have had nothing to do with starting a vehicle can inhibit starting if their ID doesn't match what is stored in the BCM. For example, the SDM, HVAC, EBCM and IPC, among others, all have IDs that must match in order for the BCM to allow starting the engine. The control modules are coded to the vehicle when they are first programmed, which results in a unique ID being permanently stored in that module.

 

The swapping issue is not unique to Global A models however, and it is increasingly difficult to keep track of which control modules cannot be swapped because it can vary depending upon electrical architecture, model, model year, sales region, vehicle option content and configuration.

 

TIP: As far as causing issues in service, the new security scheme will not present any problems as long as control modules are not swapped.

 

Problems Resulting from Swapping

 

Problems can occur when a technician attempts to swap a control module configured for one vehicle into another during the course of diagnosis or in order to expedite a repair. Symptoms such as no-start conditions and DTCs that cannot be cleared are to be expected.

 

Problems also may be introduced into vehicles that exhibit no symptoms until a later date, adding to the complexity of diagnosing the vehicle. These "sleeper issues" may be triggered only after multiple key cycles or only after battery power has been removed from the BCM. Such issues can be time consuming for the technician and Technical Assistance Center (TAC) to rectify, driving up unnecessary warranty expense and leading to customer dissatisfaction.

 

TIP: Unlike some other modules, the radio should resume working normally once it is installed back into the vehicle from which it was taken.

 

Symptoms of Module Swapping

 

A variety of symptoms may appear in a Global A vehicle containing one or more control modules swapped from a like vehicle. Depending upon which control modules have been swapped, possible symptoms include:

 

·       The VIN read by GDS and SPS does not match the vehicle.

 

·       Current DTC B3902 - Incorrect IMMO ID Rec. set in IPC, SDM, ECM, HVAC, Steering Column Lock Control Module (if equipped) or BCM. There are no warning lamps or DIC messages and this DTC cannot be cleared.

 

·       IPC module displays (- - -) for odometer and trip odometer values.

 

·       Vehicle will enter power mode only if the key fobs that match the donor vehicle BCM are included in the swap.

 

·       BCM and/or ECM has current DTC B389A - Environment Identification. There is a Service Theft System message on the DIC, the Security MIL is illuminated and this DTC cannot be cleared.

 

·       ECM odometer value is incorrect for vehicle.

 

·       Radio displays Locked

 

- Thanks to Jeff Flood, Mark Haning and Kevin Fondaw