GMC Sierra Owners Manual

Towing Equipment
Driving and Operating / Towing / Towing Equipment

Hitches

The correct hitch equipment helps maintain combination control. Many trailers can be towed with a weight-carrying hitch which simply features a coupler latched to the hitch ball, or a tow eye latched to a pintle hook. Other trailers may require a weight-distributing hitch that uses spring bars to distribute the trailer tongue weight among the two vehicle and trailer axles.

Fifth-wheel and gooseneck hitches may also be used. See “Weight of the Trailer Tongue” under Trailer Towing on page 9‑84 for rating limits with various hitch types.

If a step-bumper hitch will be used, the bumper could be damaged in sharp turns. Make sure there is ample room when turning to avoid contact between the trailer and the bumper.

Consider using sway controls with any trailer. Ask a trailering professional about sway controls or refer to the trailer manufacturer's recommendations and instructions.

Weight-Distributing Hitch Adjustment

GMS Sierra: Towing Equipment. A. Body to Ground Distance
A. Body to Ground Distance
B. Front of Vehicle

When using a weight-distributing hitch, the spring bars should be adjusted so the distance (A) is the same after coupling the trailer to the tow vehicle and adjusting the hitch.

Fifth-Wheel and Gooseneck Trailering

Fifth-wheel and gooseneck trailers can be used with many pickup models. These trailers place a larger percentage of the weight (kingpin weight) on the tow vehicle than conventional trailers. Make sure this weight does not cause the vehicle to exceed GAWR or GVWR.

Fifth-wheel or gooseneck kingpin weight should be 15 to 25 percent of the trailer weight up to the maximum amount specified in the trailering chart for the vehicle. See “Weight of the Trailer” under Trailer Towing on page 9‑84 for more information.

The hitch should be located in the pickup bed so that its centerline is over or slightly in front of the rear axle. Take care that it is not so far forward that it will contact the back of the cab in sharp turns. This is especially important for short box pickups. Trailer pin box extensions and sliding fifth-wheel hitch assemblies can help this condition.

There should be at least six inches of clearance between the top of the pickup box and the bottom of the trailer shelf that extends over the box.

Make sure the hitch is attached to the tow vehicle frame rails. Do not use the pickup box for support.

Safety Chains

Always attach chains between the vehicle and the trailer. Cross the safety chains under the tongue of the trailer to help prevent the tongue from contacting the road if it becomes separated from the hitch.

Instructions about safety chains may be provided by the hitch manufacturer or by the trailer manufacturer. If the trailer being towed weighs up to 2 271 kg (5,000 lbs) with a factory-installed step bumper, safety chains may be attached to the attaching points on the bumper; otherwise, safety chains should be attached to holes on the trailer hitch platform. Always leave just enough slack so the combination can turn. Never allow safety chains to drag on the ground.

Trailer Brakes

A loaded trailer that weighs more than 900 kg (2,000 lbs) needs to have its own brake system that is adequate for the weight of the trailer. Be sure to read and follow the instructions for the trailer brakes so they are installed, adjusted, and maintained properly.

Do not tap into the vehicle's hydraulic brake system.

Auxiliary Battery

The auxiliary battery provision can be used to supply electrical power to additional equipment that may be added, such as a slide-in camper.

If the vehicle has this provision, this relay will be located on the driver side of the vehicle, next to the underhood electrical center.

Be sure to follow the proper installation instructions included with any electrical equipment that is installed.

Notice: Leaving electrical equipment on for extended periods will drain the battery.

Always turn off electrical equipment when not in use and do not use equipment that exceeds the maximum amperage rating for the auxiliary battery provision.

Trailer Wiring Harness

The vehicle is equipped with one of the following wiring harnesses for towing a trailer or hauling a slide-in camper.

Basic Trailer Wiring

All regular, extended cab and crew cab pickups have a seven-wire trailer towing harness.

For vehicles not equipped with heavy duty trailering, the harness is secured to the vehicle's frame behind the spare tire mount. The harness requires the installation of a trailer connector, which is available through your dealer.

If towing a light-duty trailer with a standard four-way round pin connector, an adapter is available from your dealer.

Heavy-DutyTrailer Wiring Harness Package

GMS Sierra: Towing Equipment. For vehicles equipped with heavy duty trailering, the harness connector is mounted in the bumper.

For vehicles equipped with heavy duty trailering, the harness connector is mounted in the bumper.

The seven-wire harness contains the following trailer circuits:
• Yellow: Left Stop/Turn Signal
• Dark Green: Right Stop/Turn Signal
• Brown: Taillamps
• White: Ground
• Light Green: Back-up Lamps
• Red: Battery Feed*
• Dark Blue: Trailer Brake*

*The fuses for these two circuits are installed in the underhood electrical center, but the wires are not connected. They should be connected by your dealer or a qualified service center. The fuse and wire for the ITBC is factory installed and connected if the vehicle is equipped with an ITBC.

The fuse for the battery feed is not required if the vehicle has an auxiliary battery. If the vehicle does not have an auxiliary battery, have your dealer or authorized service center install the required fuse.

If charging a remote (non-vehicle) battery, press the Tow/Haul Mode button, if equipped, located at the end of the shift lever. This will boost the vehicle system voltage and properly charge the battery. If the trailer is too light for Tow/Haul Mode, or the vehicle is not equipped with Tow/Haul, turn on the headlamps as a second way to boost the vehicle system and charge the battery.

Camper/Fifth-Wheel Trailer Wiring Package

The seven-wire camper harness is located under the front edge of the pickup box on the driver side of the vehicle, attached to the frame bracket. A connector must be added to the wiring harness which connects to the camper.

The harness contains the following camper/trailer circuits:
• Yellow: Left Stop/Turn Signal
• Dark Green: Right Stop/Turn Signal
• Brown: Taillamps
• White: Ground
• Light Green: Back-up Lamps
• Red: Battery Feed
• Dark Blue: Trailer Brake

GMS Sierra: Towing Equipment. If the vehicle is equipped with the “Heavy-Duty Trailering” option, please refer to “Heavy-Duty Trailer Wiring Package” earlier in this section.

If the vehicle is equipped with the “Heavy-Duty Trailering” option, please refer to “Heavy-Duty Trailer Wiring Package” earlier in this section.

When the camper-wiring harness is ordered without the heavy-duty trailering package, a seven-wire harness with a seven-pin connector is located at the rear of the vehicle and is tied to the vehicle's frame.

Electric Brake Control Wiring Provisions

These wiring provisions are included with the vehicle as part of the trailer wiring package. These provisions are for an electric brake controller. The instrument panel contains blunt cut wires behind the steering column for the trailer brake controller. The harness contains the following wires:
• Dark Blue: Brake Signal to Trailer Connector
• Red/Black: Battery
• Light Blue/White: Brake Switch
• White: Ground

The harness should be installed by your dealer or a qualified service center.

If the vehicle is equipped with an Integrated Trailer Brake Control (ITBC) System, the blunt cuts exist, but are not connected further in the harness. If an aftermarket trailer brake controller is installed, the ITBC must be disconnected. Do not power both ITBC and aftermarket controllers to control the trailer brakes at the same time.

Tow/Haul Mode

GMS Sierra: Towing Equipment. Pressing this button at the end of the shift lever turns on and off the Tow/Haul Mode.

Pressing this button at the end of the shift lever turns on and off the Tow/Haul Mode.

GMS Sierra: Towing Equipment. This indicator light on the instrument panel cluster comes on when the Tow/Haul Mode is on.

This indicator light on the instrument panel cluster comes on when the Tow/Haul Mode is on.

Tow/Haul is a feature that assists when pulling a heavy trailer or a large or heavy load. See Tow/Haul Mode on page 9‑42 for more information.

Tow/Haul is designed to be most effective when the vehicle and trailer combined weight is at least 75 percent of the vehicle's Gross Combined Weight Rating (GCWR).

See “Weight of the Trailer” under Trailer Towing on page 9‑84. Tow/ Haul is most useful under the following driving conditions:

• When pulling a heavy trailer or a large or heavy load through rolling terrain.

• When pulling a heavy trailer or a large or heavy load in stop-and-go traffic.

• When pulling a heavy trailer or a large or heavy load in busy parking lots where improved low speed control of the vehicle is desired.

Operating the vehicle in Tow/Haul when lightly loaded or with no trailer at all will not cause damage.

However, there is no benefit to the selection of Tow/Haul when the vehicle is unloaded. Such a selection when unloaded may result in unpleasant engine and transmission driving characteristics and reduced fuel economy. Tow/ Haul is recommended only when pulling a heavy trailer or a large or heavy load.

Integrated Trailer Brake Control System

GMS Sierra: Towing Equipment. The vehicle may have an Integrated Trailer Brake Control (ITBC) system for electric trailer brakes.

The vehicle may have an Integrated Trailer Brake Control (ITBC) system for electric trailer brakes.

This symbol is located on the Trailer Brake Control Panel on vehicles with an Integrated Trailer Brake Control system. The power output to the trailer brakes is based on the amount of brake pressure being applied by the vehicle’s brake system. This available power output to the trailer brakes can be adjusted to a wide range of trailering situations.

The ITBC system is integrated with the vehicle’s brake, antilock brake, and StabiliTrak (if equipped) systems. In trailering conditions that cause the vehicle’s antilock brake or StabiliTrak systems to activate, power sent to the trailer's brakes will be automatically adjusted to minimize trailer wheel lock-up. This does not imply that the trailer has StabiliTrak.

Non-hybrid vehicles with StabiliTrak have a Trailer Sway Control (TSC) feature. See Trailer Sway Control (TSC) on page 9‑112.

Non-hybrid vehicles with StabiliTrak have a Hill Start Assist (HSA) feature. See Hill Start Assist (HSA) on page 9‑59.

If the vehicle’s brake, antilock brake, or StabiliTrak systems are not functioning properly, the ITBC system may not be fully functional or may not function at all. Make sure all of these systems are fully operational to ensure full functionality of the ITBC system.

The ITBC system is powered through the vehicle's electrical system. Turning the ignition off will also turn off the ITBC system. The ITBC system is fully functional only when the ignition is in ON or in RUN.

The ITBC system can only be used with trailers with electric brakes.

WARNING
Connecting a trailer that is not compatible with the ITBC system may result in reduced or complete loss of trailer braking. There may be an increase in stopping distance or trailer instability which could result in personal injury or damage to the vehicle, trailer, or other property. An aftermarket controller may be available for use with trailers with surge, air, or electric-over-hydraulic trailer brake systems. To determine the type of brakes on the trailer and the availability of controllers, check with your trailer manufacturer or dealer.

When trailering, make sure of the following:
• The ITBC system is used only with trailers that are equipped with electric brakes.
• All applicable local and federal laws and regulations are followed.
• All electrical and mechanical connections to the trailer are made correctly.
• The trailer’s brakes are in proper working condition.
• The trailer and vehicle are properly loaded for the towing condition.

The ITBC system is a factory-installed item. Out-of-factory installation of this system should not be attempted. GM is not responsible for warranty or performance of the system resulting from out-of-factory installation.

Trailer Brake Control Panel

GMS Sierra: Towing Equipment. A. Manual Trailer Brake Apply Lever
A. Manual Trailer Brake Apply Lever
B. Trailer Gain Adjustment Buttons

The ITBC system has a control panel located on the instrument panel to the left of the steering column. See Instrument Panel (Base/Uplevel Version) on page 1‑2 or Instrument Panel (Premium Version) on page 1‑6 for more information. The control panel allows adjustment to the amount of output, referred to as trailer gain, available to the electric trailer brakes and allows manual application of the trailer brakes. The Trailer Brake Control Panel is used along with the Trailer Brake Display Page on the DIC to adjust and display power output to the trailer brakes.

Trailer Brake DIC Display Page

The ITBC system displays messages on the vehicle’s Driver Information Center (DIC). See Driver Information Center (DIC) on page 5‑33 for more information.

The display page indicates Trailer Gain setting, power output to the electric trailer brakes, trailer connection, and system operational status.

The Trailer Brake Display Page can be displayed by performing any of the following actions:

• Scrolling through the DIC menu pages using the odometer trip stem or the DIC Vehicle Information button (if equipped).

• Pressing a Trailer Gain button—If the Trailer Brake Display Page is not currently displayed, pressing a Trailer Gain button will first recall the current Trailer Gain setting. After the Trailer Brake Display Page is displayed, each press and release of the gain buttons will then cause the Trailer Gain setting to change.

• Activating the Manual Trailer Brake Apply lever.

• Connecting a trailer equipped with electric trailer brakes.

All DIC warning and service messages must first be acknowledged by the driver by pressing the odometer trip stem or the DIC Vehicle Information button (if equipped) before the Trailer Brake Display Page can be displayed and Trailer Gain can be adjusted.

TRAILER GAIN: This setting is displayed any time the Trailer Brake Display Page is active. This setting can be adjusted from 0.0 to 10.0 with either a trailer connected or disconnected. To adjust the Trailer Gain, press one of the Trailer Gain adjustment buttons located on the Trailer Brake Control Panel. Press and hold a gain button to cause the Trailer Gain to continuously adjust.

To turn the output to the trailer off, adjust the Trailer Gain setting to 0.0 (zero).

0.0 (zero) gain is the factory default setting. To properly adjust trailer gain, see “Trailer Gain Adjustment Procedure” later in this section.

TRAILER OUTPUT: This is displayed any time a trailer with electric brakes is connected. Output to the electric brakes is based on the amount of vehicle braking present and relative to the Trailer Gain setting. Output is displayed from 0 to 10 bars for each gain setting.

Non-hybrid vehicles with Trailer Sway Control (TSC) or Hill Start Assist (HSA), output to the electric trailer brakes may be displayed when the systems are active. See Trailer Sway Control (TSC) on page 9‑112 and Hill Start Assist (HSA) on page 9‑59.

The Trailer Output will indicate “- - - - - -” on the Trailer Brake Display Page whenever the following occur:
• No trailer is connected
• A trailer without electric brakes is connected (no DIC message is displayed)
• A trailer with electric brakes has become disconnected (a CHECK TRAILER WIRING message will also be displayed on the DIC)
• There is a fault present in the wiring to the electric trailer brakes (a CHECK TRAILER WIRING message will also be displayed on the DIC)
• There is a fault in the ITBC system (a SERVICE TRAILER BRAKE SYSTEM message will also be displayed in the DIC)

Manual Trailer Brake Apply

The Manual Trailer Brake Apply Lever is located on the Trailer Brake Control Panel and is used to apply the trailer’s electric brakes independent of the vehicle’s brakes.

This lever is used in the Trailer Gain Adjustment Procedure to properly adjust the power output to the trailer brakes. Sliding the lever to the left will apply only the trailer brakes.

The power output to the trailer is indicated in the Trailer Brake Display Page on the DIC. If the vehicle’s service brakes are applied while using the Manual Trailer Brake Apply Lever, the trailer output power will be the greater of the two.

The trailer's and the vehicle's brake lamps will come on when either vehicle braking or manual trailer brakes are applied.

Trailer Gain Adjustment Procedure

Trailer Gain should be set for a specific trailering condition and must be adjusted any time vehicle loading, trailer loading, or road surface conditions change.

Setting the Trailer Gain properly is needed for the best trailer stopping performance. A trailer that is over-gained may result in locked trailer brakes. A trailer that is under-gained may result in not enough trailer braking. Both of these conditions may result in poorer stopping and stability of the vehicle and trailer.

Use the following procedure to correctly adjust Trailer Gain for each towing condition:

1. Make sure the trailer brakes are in proper working condition.

2. Connect a properly loaded trailer to the vehicle and make all necessary mechanical and electrical connections. See Vehicle Load Limits on page 9‑17 for more information.

3. After the electrical connection is made to a trailer equipped with electric brakes:

• A TRAILER CONNECTED message will be briefly displayed on the DIC.

• The Trailer Brake Display Page will appear on the DIC showing TRAILER GAIN and TRAILER OUTPUT.

• In the Trailer Output display on the DIC, “- - - - - -” will disappear if there is no error present. Connecting a trailer without electric brakes will not clear the six dashed lines.

4. Adjust the Trailer Gain by using the gain adjustment (+ / -) buttons on the Trailer Brake Control Panel.

5. Drive the vehicle with the trailer attached on a level road surface representative of the towing condition and free of traffic at about 32 to 40 km/h (20 to 25 mph) and fully apply the Manual Trailer Brake Apply Lever.

Adjusting trailer gain at speeds lower than 32 to 40 km/h (20 to 25 mph) may result in an incorrect gain setting.

6. Adjust the Trailer Gain to just below the point of trailer wheel lock-up, indicated by trailer wheel squeal or tire smoke when a trailer wheel locks.

Trailer wheel lock-up may not occur if towing a heavily loaded trailer. In this case, adjust the Trailer Gain to the highest allowable setting for the towing condition.

7. Re-adjust Trailer Gain any time vehicle loading, trailer loading or road surface conditions change or if trailer wheel lock-up is noticed at any time while towing.

Other ITBC-Related DIC Messages

In addition to displaying TRAILER GAIN and TRAILER OUTPUT through the DIC, trailer connection and ITBC system status are displayed on the DIC.

TRAILER CONNECTED: This message will be briefly displayed when a trailer with electric brakes is first connected to the vehicle. This message will automatically turn off in about 10 seconds. The driver can also acknowledge this message before it automatically turns off.

CHECK TRAILER WIRING: This message will be displayed if:

1. The ITBC system first determines connection to a trailer with electric brakes and then the trailer harness becomes disconnected from the vehicle.

If the disconnect occurs while the vehicle is stationary, this message will automatically turn off in about 30 seconds. This message will also turn off if the driver acknowledges this message or if the trailer harness is re-connected.

If the disconnect occurs while the vehicle is moving, this message will continue until the ignition is turned off. This message will also turn off if the driver acknowledges this message or if the trailer harness is re-connected.

2. There is an electrical fault in the wiring to the electric trailer brakes. This message will continue as long as there is an electrical fault in the trailer wiring. This message will also turn off if the driver acknowledges this message.

To determine if the electrical fault is on the vehicle side or trailer side of the trailer wiring harness connection, do the following:

1. Disconnect the trailer wiring harness from the vehicle.

2. Turn the ignition off.

3. Wait 10 seconds, then turn the ignition back to RUN.

4. If the CHECK TRAILER WIRING message re-appears, the electrical fault is on the vehicle side.

If the CHECK TRAILER WIRING message only re-appears when connecting the trailer wiring harness to the vehicle, the electrical fault is on the trailer side.

SERVICE TRAILER BRAKE SYSTEM: This message will be displayed when there is a problem with the ITBC system. If this message persists over multiple ignition cycles, there is a problem with the ITBC system.

Take the vehicle to an authorized GM dealer to have the ITBC system diagnosed and repaired.

If either the CHECK TRAILER WIRING or SERVICE TRAILER BRAKE SYSTEM message is displayed while driving the vehicle, power is no longer available to the trailer brakes. When traffic conditions allow, carefully pull the vehicle over to the side of the road and turn the ignition off. Check the wiring connection to the trailer and turn the ignition back on. If either of these messages continues, either the vehicle or trailer needs service.

An authorized GM dealer may be able to diagnose and repair problems with the trailer. However, any diagnosis and repair of the trailer is not covered under the vehicle warranty. Please contact your trailer dealer for assistance with trailer repairs and trailer warranty information.


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