For everything from saving on automobile insurance to connecting aftermarket cruise control, there are now a number of devices that owners plug into the Data Link Connector (DLC), or Assembly Line Diagnostic Link (ALDL). However, any unauthorized device connected to the DLC may cause a variety of hard-to-diagnose conditions.
Many of the problems caused by devices connected to the DLC are communication issues on the High Speed Controller Area Network (HSCAN) bus. An additional issue with diagnosing these conditions is that many times the device itself may be removed by customers when their vehicle is brought in for service.
Many possible problems are caused by an open connection on the HSCAN bus. For example, if the device only makes connection with one CAN +, it will cause bus errors and strange control module behavior.
The various issues described by customers with their vehicles are often related to high- or low-speed data bus traffic. The conditions can be extremely varied, but some known issues are:
• Radio will not turn off after turning off the vehicle
• Bus or LAN traffic stays active, leading to a discharged battery
• Problems reprogramming control modules either because of interference or the device will not allow the bus to power down
• Interference with OnStar’s ability to provide diagnostic data
• Engine and transmission performance issues with the Check Engine light on
• Intermittent stalling
• Reduced power DIC messages and DTCs
• StabiliTrak DIC messages and DTCs
• DTC C0561 (System Disabled Information Stored Invalid Data) in the Electronic Brake Control Module (EBCM) leading to a traction control issue
• No High Speed LAN communication along with various DTC communication U-codes
• Transmission will not shift for one key cycle (TCM in default mode)
• Instrument cluster gauges erratic or flickering
• Service Engine Soon or Check Engine MIL illuminated and numerous DTC communication codes such as U0100 (Lost Communication With Engine Control Module), U0101 (Lost Communication With Transmission Control Module), U186B (Electronic Brake Control Module Lost Communication with Transmission Control Module) and U1862.
• Diesel power-up devices resulting in no power in 4WD Low range
• Service Tire Pressure Monitor System MIL illuminated; cannot relearn the Tire Pressure Monitor System
• Hybrid issues regarding reduced propulsion power DIC messages and service high voltage charging system DIC messages
TIP: The Diagnostic System Check – Vehicle (the starting point for any diagnostic procedure) in the Service Information calls out that there should not be any aftermarket devices connected or installed that affect the operation of the system. Additional information under Checking Aftermarket Accessories explains how to check for aftermarket accessories. The Diagnostic System Check Instructions link at the top of the Diagnostic System Check – Vehicle procedure also provides further information about aftermarket accessories and their possible negative effect on the vehicle.
During diagnosis, if nothing else can be identified as the root cause of the condition, check for a device plugged into the DLC.
If a device is available, attempt to duplicate the condition. Remove the device to determine if the condition is eliminated. If confirmed, inform the customer of the issue and that it will be necessary to work with the supplier of the device for further resolution. If the condition is not eliminated, continue with the diagnostics in the appropriate Service Information.
If any parts appear to have been damaged by the device or the installation of the device, document on the repair order what was identified on the vehicle. This would not be covered under the New Vehicle Limited Warranty.
Connected devices may be used for such things as tracking and/or maintenance interval scheduling (more common on fleet and rental vehicles) (Fig 3), insurance monitoring that automatically keeps track of the vehicle’s driving record (Fig. 4), aftermarket cruise control (Fig. 5), police speed checking (RADAR or LIDAR) and other aftermarket components.
Sometimes, an aftermarket device has another DLC on it and the rest of the harness is tucked out of sight underneath the instrument panel, making it not completely obvious to the technician while still allowing diagnostic tools to be used. (Fig. 6)
Certain aftermarket devices connected to the DLC may interfere with OnStar’s ability to perform a diagnostic probe when requested (via a blue button call) by a subscriber. These devices also prohibit the ability to gather diagnostic and tire pressure data for a subscriber’s scheduled OnStar Vehicle Diagnostic (OVD) e-mail.
These aftermarket devices use the vehicle’s serial data bus to perform data requests and/or information gathering. When these devices are requesting data, OnStar is designed not to interfere with any data request being made by these devices as required by OBD II regulations.
When performing a diagnostic check for an unsuccessful or incomplete OnStar diagnostic probe, or for concerns regarding completeness of the OVD e-mail, verify that an aftermarket device was not present at the time of the requested probe.
If an aftermarket device is interfering (including a scan tool of any type), the OVD e-mail will consistently display a “yellow” indication in the diagnostics section for all vehicle systems except the OnStar System, and the tire pressure data (not available on all vehicles) will not be displayed (i.e. the section is collapsed).
Refer to Bulletin #08-08-46-004A for additional information on OnStar Diagnostic Services.
– Thanks to B.J. Lackey