Models: GM vehicles with serial data bus

Condition

Customers may comment on various issues with their vehicle related to high- or low-speed data bus traffic. These concerns may be widely varied, but some of the known issues are listed on the next page. The information contained in this bulletin is not meant to single out any one device or symptom, but to provide additional information that may be useful for diagnosing issues that do not have other diagnostic methods to identify the root cause.

Note: This bulletin is being written with a focus on full-size trucks and full-size vans along with other fleet vehicles, but it could apply to any vehicle.

Known Symptoms (not specific to any one device)

• The radio may not shut off after shutting down vehicle.

• Bus or LAN traffic may stay active leading to a discharged vehicle battery.

• Problems reprogramming modules either because of interference or the device will not allow the bus to power down.

• ONSTAR loses the ability to provide diagnostic data.

• Various engine and transmission performance issues with SES light set.

• Intermittent driveability issues.

• Reduced power message and codes.

• Stabilitrak message and codes.

• C0561 stored in the EBCM leading to a traction control issue.

• No high-speed LAN communication along with various communication U-codes.

• Transmission may not shift for one key cycle (TCM in default mode).

• Erratic gauge readings or flickering displays.

• SES, MIL or CEL light set and numerous DTC communication codes such as U0100, U0101, U186B and U1862.

• Diesel power-up devices causing no power in 4WD low range.

• Erratic electric power steering boost potentially associated with codes U2109, U2107, U2100, B1325, C0000.

• Battery run-down

• Service Tire Pressure Monitoring (TPM) system light illuminated.

– Cannot relearn TPM sensors

• Specific to Hybrids:

• Reduced propulsion power message.

• Service high-voltage charging system
message.

Cause

If nothing else can be identified as the root cause of the issue after normal diagnostics as found in the service information, check for a device plugged into the Assembly Line Diagnostic Link (ALDL) or Data Link Connector (DLC) for tracking and/or maintenance interval scheduling. Monitoring devices, along with other electronic accessories such as aftermarket cruise control, or police speed checking devices (RADAR or LIDAR), may cause one or more of the concerns listed previously.

Many of the problems described could be caused by an open connection on the HSCAN bus. Example: if the device only makes connection with one CAN +, then it will cause bus errors and erratic ECU behavior.

These devices may be removed by the customer for use in another vehicle while theirs is brought in for service. The intent of this bulletin is to identify a potential source of concerns that do not have other diagnostic methods to identify them.

Courtesy of ALLDATA.