Electric Power Steering (EPS)

For several years, GM vehicles have offered steering systems involving electronics. The Magnasteer system (TechLink Dec. 2000) uses an electronically controlled magnetic unit to vary the amount of effort needed to steer the vehicle. Quadrasteer (TechLink, Dec 2001) uses an electronically controlled electric motor to provide steering for the rear wheels.

Now, the 2004 Chevrolet Malibu is offering an Electric Power Steering (EPS) system (fig. 1), which uses an electric motor to provide steering assist to the front wheels. This eliminates the power steering pump, hoses, control valve and piston/cylinder assembly.

The EPS motor provides a variable amount of assist directly to the steering shaft, based on vehicle speed and input torque. The motor and the Power Steering Control Module (PSCM) are mounted as an assembly directly to the steering column.

TIP: Unlike Magnasteer, which is controlled by the Electronic Brake Control Module, the EPS has its own control module.

The EPS motor is a 65 amp, brushless, 12-volt reversible unit. It drives the steering shaft through a worm shaft and 22:1 reduction gear.

This method of providing boost is considerably different from a hydraulic assist. In the hydraulic system, pressure is applied directly to the steering rack to help move it side to side. On the EPS system, boost is applied to the steering shaft, which helps the driver turn the steering pinion.

Because the electric motor draws a large amount of current when it is running, the system has built-in overload protection. Heat build-up may be a factor at high ambient temperatures, when a large amount of steering wheel movements occur in a short period of time (such as repeatedly performing lock-to-lock turns, while standing still). It’s unlikely that a customer will experience this.

The software in the controller keeps track of current usage and compares that with the known heat buildup of various components. If a heat threshold is reached, the controller uses pulse width modulation (PWM) to temporarily limit current to the motor. This is called de-rating. In this rare instance, the driver would notice a temporary reduction in boost.

The EPS control module depends on various inputs:
- Vehicle speed
- Steering shaft torque sensor
- Steering wheel position sensor

In a hydraulic power steering system, the input and output steering shafts are joined by a small torsion bar. Two halves of a hydraulic flow valve are attached, one to each shaft. When torque is applied, the torsion bar twists, the valve halves move relative to each other, and fluid is allowed to flow. In the electric power steering system, the upper and lower torque sensor rotors, which use resistive elements, are mounted to the input and output shafts. When torque is applied, the torsion bar twists, the rotors move relative to each other, and the movement affects the difference in resistance between the two rotors. This electrical information is used by the PSCM as the torque input. Boost is provided, proportional to torque. The combined torque/hand wheel position sensor assembly is contained within the steering column.

Each EPS unit is calibrated for the vehicle in which it is installed, which ensures the proper amount of assist and road feel. The calibration is called the Steering Tuning Selection and is specific to the vehicle’s VIN. It can be read from the module, using the Tech 2.

Service
The EPS motor and control unit are replaceable as an assembly. The torque sensor and steering wheel position sensor are serviced by replacing the steering column assembly.

If components are replaced in the EPS system, it is necessary to perform a hand wheel position sensor calibration so the system knows where the center position is for the steering wheel.

There’s a torque sensor zero calibration, which affects on-center effort bias.

And, the correct Steering Tuning Selection will also have to be made so the system knows which boost curve to use for that particular vehicle.

Diagnosis
Diagnosis of the EPS system is aided by the following data readouts using the Tech 2 scan tool:
- Battery Voltage
- Calculated System Temperature
- Engine Speed
- Motor Command
- Motor Feedback
- Steering Shaft Torque
- Steering Position Sensor
- Steering Tuning Selection
- Steering Wheel Position
- Torque Sensor Signal
- Vehicle Speed

The PSCM module communicates using the GMLAN network.

- Thanks to David Juarez

Background
As the complexity of GM vehicles has increased, so has the need for additional DTC (Diagnostic Trouble Code) numbers.

For a given circuit or circuit type, 5 consecutive DTC numbers were usually assigned in the following format:
B2700 Ignition Shift Interlock Circuit (base number)
B2701 Ignition Shift Interlock Circuit Range/Performance
B2702 Ignition Shift Interlock Circuit Low
B2703 Ignition Shift Interlock Circuit High
B2704 Ignition Shift Interlock Circuit Open

For some circuits, not all 5 of the assigned DTCs were actually needed. But because assignments were made according to the formatting plan, many new types of circuits consumed 5 numbers.

The list of numbers available for DTCs used on GM vehicles worldwide was being rapidly depleted.

When the message structure of the GMLAN Serial Data Network was being developed (see March 2003 TechLink), an additional byte of data was included in each DTC Message. So, additional information could be displayed on the scan tool for a circuit failure without assigning more than one DTC number to a given circuit. This extra data is being called the DTC Symptom.

This byte of data can be indicated with two alphanumeric characters. The first character following the DTC indicates the DTC Symptom category and the second character indicates the subtype of the DTC Symptom. There’s a complete list of categories and subtypes in SI under the 2004 XLR or the 2004 Malibu. Follow this path:
- “Build” the vehicle
- Vehicle Control Systems
- Vehicle DTC Information
- Description and Operation
- DTC Symptom Description

Display of DTC Symptoms
When DTC Symptoms are available on the scan tool, they will be displayed separately from the DTC number (fig 2).

Service Information will also deal specifically with DTC Symptoms. Information about the DTC Symptom(s) will be provided in the facing page information for a DTC. See the accompanying sample from a facing page (fig. 3).

In many cases, the diagnostic procedure in Service Information is the same for a given DTC regardless of DTC Symptom. In some cases, different diagnostic procedures will be used for different DTC Symptoms with the same base DTC number. In either case, use the Search function in ESI to find DTCs by base DTC number only, and if necessary, select the appropriate procedure for the DTC Symptom after the search.

A special case of the DTC Symptom is when the base DTC is the only malfunction identified. Additional information that a DTC symptom would provide is not needed or recorded by the module. The base DTC number and descriptor provide all the information that is available. In that case, the DTC Symptom displayed is 00 (No Additional Information). If 00 is displayed as a DTC Symptom, there is not a fault with DTC display on the scan tool; it is just indicating that no additional information is available..

- Thanks to Gary Clark

figure 2

At present, radios are programmable on the following vehicles:
2003 C/K vehicles
2003 G/H vans
2003-04 Hummer H2
2004 all light and medium duty trucks

These radios must be programmed when a new unit is installed or radios are swapped. In the past, it was necessary to call the Techline Customer Support Center for a VCI number to complete the event. The new process makes this phone call unnecessary.

Requirements
To use this procedure, you must be using TIS satellite version 9.0 and Tech 2 software version 23.005 (or newer). This coverage was released in late August.

Procedure
You will need the following information before you begin:
- RPO code of the radio you’re going to program
- RPO code of speakers
- On C/K trucks, observe if there’s a Y91 amplifier package
- On Hummer H2, observe if there’s a Y91, Y92, or no amp package
- Be aware that RPO UC6 is a six-disc in-dash CD changer.

TIP: On vehicles with RPO U42 DVD player, you must pull the DVD fuse before programming the radio.

TIP: You must install the radio to be programmed in the vehicle before beginning the request process.

Begin by requesting information from the vehicle. The Tech 2 will gather:
- Calibration numbers
- VIN
- Radio’s 8-digit GM part number

Connect the Tech 2 to a PC with the TIS application. The next part of the process is automated and transparent. TIS will obtain the VIN and radio 8-digit part number from your Tech 2, and will then locate and display the appropriate Option Screen. In the turquoise area of the display (fig. 4), make the necessary selection, based on the known radio RPO.

Fill in other option selections as required; i.e., HVAC.

TIP: Ordinarily, the Radio Part Number Select popup will not appear, because TIS will obtain the number from the Tech 2. But if the popup does appear (fig. 5), it may be because
- The Tech 2 does not contain software version 23.005 or newer. In this case, you must manually select the correct radio part number from the list provided. You can obtain the number from the tag on the radio, or by using the Tech 2 Diagnostic Functions to read the number from the radio.
- Something is wrong with the radio.

On the Supported Controller screen, select Radio and select Normal. Then when the Calibration screen appears, deal with each available tab, one at a time (fig. 6).

Under the Tuner tab, specify the country in which the radio will be operated. This affects the range of frequencies displayed.

Under the Audio tab, you will need to make a selection based on the radio’s RPO code.

Under the Equalizer tab, you need to know and specify the vehicle’s cabin and speaker configuration. This affects how the radio sounds in its surroundings.
Return to the vehicle and download the programming data to the radio.

TIP: If you make any errors during the selection process, improper calibrations could result in no audio and/or no chime functions. (The radio will light up but has no volume.) If this occurs, DO NOT replace the radio. Start the selection and calibration process again.

Finally, as with any programming event, check for codes.

- Thanks to Chris Jenkins, Craig Jones and Mark Stesney

Corrections

An article in the July 2003 issue of TechLink involving Switch Plate Bezel Removal contains an error in the applicable model years. It applies to 2003 - 04.

An article in the August 2003 issue involving Front Stabilizer Shaft Installation refers to 2003 vehicles. It should have said 2004.

There’s a lot of news about XM™ Satellite Radio for the 2004 model year.

New Models Added
First, a number of additional vehicles will be offering XM radio in 2004: Canyon, Colorado, Envoy, Envoy XL, Envoy XUV, Grand Prix, Ion, Malibu, Malibu Maxx, Montana, Rainier, SRX, Trail Blazer, Trail Blazer EXT, Venture, Vibe, Vue, and XLR.

All vehicles that offered XM radio in the past will continue for 2004.

New Antenna Technology
Beginning with the 2004 model year, a new XM antenna is being installed on some vehicles (fig. 7). The list includes Avalanche, Denali, Denali XL, Escalade, Escalade ESV, Escalade EXT, Sierra, Silverado, Suburban, Tahoe, Yukon, and Yukon XL. The DeVille, Seville, Bonneville, and LeSabre will switch to this new antenna mid-year. And also mid-year, the 2004 Envoy, Envoy XL, Envoy XUV, Rainier, TrailBlazer, and TrailBlazer EXT will switch to a different new antenna (fig. 8).

The XM antenna used in the 2002-03 model years included two different elements, one to receive signals from the satellites, and a second one to receive signals from the ground repeaters. Two coax cables were required. The new antennas use one element to receive both sets of signals, and only one coax cable is required.

TIP: The two types of antenna cannot be interchanged in service.

XM Radio Activation
At present, all vehicles with XM radio arrive at the dealership with ten rotating free-to-air channels. It’s necessary to phone XM radio at 800.556.3600 to activate the service. Beginning in October, the ten free-to-air channels will be phased out. Dealers will be able to activate all of the vehicles on their lot through a process called Rapid Activation, turning all of their vehicles into XM demonstrators. The only information needed to Rapid-Activate a vehicle is the 8-digit XM radio ID, obtained by tuning to XM channel 0.

TIP: When a customer buys an XM-equipped vehicle that has been Rapid Activated, an account is automatically set up at XM, when the Customer Delivery Record is received.

Beginning early in calendar year 2004, all vehicles will arrive pre-activated from the factory. Each customer will have several choices:
1. Accept the vehicle with the radio activated and enjoy 3 months of free service before deciding to continue. XM will send information to the customer about extending their subscription.
2. Sign up for a multi-year subscription.
3. Tell the dealer that they are not interested in 3 months of free service.

Theftlock
To deter theft, all XM receivers are programmed to learn the VIN of the vehicle in which they are installed, using the Class 2 data line. As soon as the VIN is learned, the unit becomes “locked.” That is, it cannot be moved to a vehicle with a different VIN -- it will not work. Once locked, the receiver can be installed only in the original vehicle.

Cadillac XLR Antenna
On the XLR, the XM radio antenna must be installed during new vehicle preparation, if the customer desires XM service. This is explained on an instruction sheet accompanying the vehicle. It is also highlighted in an accompanying article.

TIP: All XLR service stock antennas are unpainted, and must be painted before installation.

Other
XM radio receivers are still on a parts restriction. After diagnosis, call GM TAC at 877.446.8227. (The prompt for XM radio is combined with the OnStar prompt.) After verifying your diagnosis, the TAC consultant will order a replacement. Use the supplied pre-paid return label to return the original receiver to avoid a non-return core charge.

Soon, you will be able to use the Tech 2 to read the serial number from the XM radio receiver. TechLink will publish the necessary path when it becomes available.

The XM antenna is molded of black plastic. Do not attempt to apply paint or clearcoat; doing so can reduce system performance. This does not apply to the Cadillac XLR antenna.

The factory location for each antenna was optimized for performance by GM engineering. Do not attempt to relocate the antenna, as this can cause degraded performance.

And finally, the antenna needs to be attached to a solid surface. Do not install cloth or vinyl roof covers on XM-equipped vehicles. This may cause degraded performance and could also lead to water leaks.

- Thanks to Doug McKibbon

Console Latch Lubricant

When a 2004 Cadillac XLR is ordered with the optional XM radio, the antenna is shipped loose. It must be installed before delivery of the vehicle (at customer request). A detailed instruction sheet is supplied with the antenna kit. Here are some highlights.

TIP: Install protective coverings over the rear compartment and adjacent panels. The folding top must be in the lowered position and the compartment lid open.

On all XLR models, an AM/FM antenna ground plate is attached to the underside of the rear compartment lid. A supplemental ground plate/template is supplied with the XM antenna. It must be positioned and installed before the XM antenna is installed (fig. 10).

A Template

TIP: For the first several months of production, it will be necessary to temporarily remove the large ground plate from the underside of the rear compartment lid. In later production, it will be reshaped and can be left in place. The instruction sheet provided with the antenna kit will reflect the appropriate steps.

The XM antenna ground plate/template aligns to a recessed feature in the rear compartment lid. It serves as a template to mark the locations for two pilot holes on the underside of the rear compartment lid.

A strip of masking tape is used to protect the exterior surface of the compartment lid while the pilot holes are enlarged as instructed.

TIP: After the pilot holes are drilled and enlarged, remove masking tape and drilling remnants and use GM RTV silicone rubber sealant (12345739) to seal the raw edges of the holes.

The XM antenna ground plate/template is equipped with an adhesive material. Peel the backing and install the plate to the underside of the compartment lid.

TIP: When the backing is removed, be sure the diecut discs are also removed from the mounting holes.

Then follow the instructions to install the XM antenna, fasteners, and wiring.

On early models, follow SI procedures to reinstall the large ground plate to the rear compartment lid. On later models, this step will not be necessary.

Then use your Tech 2 to verify that the proper parameters are displayed, and clear DTCs, following the instruction sheet.

The vehicle is now ready for the XM radio receiver to be activated.

- Thanks to Jason Macco

figure 10

Cadillac XLR Trim Removal

Here are some tips to help avoid damage when removing the console trim pieces on the new Cadillac XLR.

The two trim pieces are the console trim plate (which surrounds the shifter and cupholder) and the instrument panel trim plate (which surrounds the radio and HVAC controls).

Both of these trim pieces are retained by metal clips (fig. 11), which must be loosened by prying.

TIP: Use a plastic trim removal stick, to avoid damage to the trim or surrounding areas.

TIP: Be sure all clips are loosened before pulling on the trim plates, to avoid deforming the metal covering.

Refer to SI for the complete procedure. The information here is additional tips.

The console trim plate comes out first. Use a T-15 Torx bit to remove the shifter handle. Then insert the trim removal stick under the edge of the trim plate in the area of the rear clip and loosen the clip (fig. 12). Repeat this for each clip, then lift the trim plate off the console. Refer to the photo for the clip locations (fig. 13).

With the console trim removed, you can remove the IP trim plate. Insert the trim stick at the upper corner and loosen the top clips (fig. 14). Work down the sides and loosen the center and bottom clips. Then remove the trim plate. Refer to the photo for clip locations (fig. 15).

- Thanks to Brad Thacher

figure 11

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