Diagnostic Aids
- The procedures used in this document are written to diagnose a concern with the customer's vehicle with no trailer connected. A concern with the customer's trailer may be the actual cause for a DTC setting or a circuit fault.
- Some customers may experience an intermittent "Check Trailer Wiring" message and/or a "Service Trailer Brake" message with DTC C1114. These concerns may be caused by a poor connection at the 7-way trailer connector. There are several manufacturers of 7-way (trailer side) connectors and many do not comply with the Society of Automotive Engineers (SAE) standard specifications. Some 7-way (trailer side) connector plugs may not properly engage the truck's 7-way connector socket and cause open circuits. Also, they may cause deformation and excessive wear of the terminals on the truck's 7-way connector socket. Over time, this will lead to poor terminal tension between the 7-way (trailer side) connector plug and the truck's 7-way connector socket. Since the trailer brake control module is always monitoring the vehicle and trailer circuits/components, a poor connection at the 7-way connector may cause a "Check Trailer Wiring" message on the driver information center.
- Engineering has recommended the use of Pollak Heavy Duty 7-way (trailer side) connector plugs. Pollak is the Original Equipment Manufacturer (OEM) of the truck's 7-way connector socket. The use of a Pollak Heavy Duty 7-way (trailer side) connector plug will ensure proper fit when the two connectors are mated.
- If the truck's 7-way connector socket terminals are deformed or have excessive wear, it will be necessary to replace the truck side connector (use Genuine GM Parts) along with the trailer's 7-way connector plug using Pollak HD connector plugs.
- Refer to PIT5311 for additional information.