Electronic Power Steering System - Variable Effort Steering: Diagnosis Chevrolet Tahoe II

Diagnostic Starting Point - Variable Effort Steering

Begin the system diagnosis with the Diagnostic System Check - Variable Effort Steering . The Diagnostic System Check will provide the following information

1. The identification of the control modules which command the system.
2. The ability of the control modules to communicate through the serial data circuit.
3. The identification of any stored diagnostic trouble codes (DTCs) and their status.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Scan Tool Output Controls

There are 2 Variable Effort Steering (VES) Output Controls tables. The first table is used for vehicles W/O Real Time Damping (RTD). In these vehicles the VES system is controlled by the Body Control Module (BCM). The second table is for vehicles W/RTD. In these vehicles the VES system is controlled by the Electronic Suspension Control (ESC) module. Use the scan tool's Special Functions selection in order to cycle ON and OFF the following

NOTE: The BCM/ESC stores the DTCs scan tool data and special functions. However, the scan tool menu to access variable effort steering is located in chassis.

BCM (W/O RTD)

ESC Module (W/RTD)

Scan Tool Data List

NOTE: The BCM/ESC stores the DTCs scan tool data and special functions. However, the scan tool menu to access variable effort steering is located in chassis.

The Variable Effort Steering (VES) Scan Tool Data Lists contain all the VES related parameters that are available on the scan tool. The parameters in the lists are arranged in alphabetical order. The column, "Data List," indicates the location of the parameter within the scan tool menu selections.

There are two VES Scan Tool Data List tables. The first table is for vehicles not equipped with Real Time Damping (RTD). In these vehicles the VES system is controlled by the Body Control Module (BCM). The second table is for vehicles equipped with RTD. In these vehicles the VES system is controlled by the Suspension Control Module. Use the VES Scan Tool Data Lists as directed by the diagnostic table or in order to supplement the diagnostic procedures. Begin all of the diagnostic procedures with the Variable Effort Steering diagnostic System Check. Use the VES Scan Tool Data Lists after the following is determined

1. There is no published DTC procedure nor published symptom procedure for the customer concern.
2. The DTC or symptom diagnostic procedure indicated by the diagnostic system check does not resolve the customer concern.

The Typical Data Values are obtained from a properly operating vehicle under the conditions specified under the first row of the Scan Tool Data List table. Comparison of the parameter values from the suspect vehicle with the Typical Data Values may reveal the source of the customer concern. These Typical Data Values may vary some what from the suspect vehicle values.

This is a system that uses the BCM not the EBCM for EVO control, data is viewed in Chassis not BCM.

Electronic Variable Orifice

RTD Autoride/EVO

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

The Steering Wheel Position Sensor is a 0-5 volt device which is used to sense steering wheel position and turning speed. The valid output or signal voltage range from the sensor is 0.35-4.75 volts. The signal voltage will increase or decrease within the valid voltage range as the steering wheel is turned. The sensor has 2 output signals, signal 1 and signal 2. Both signals are used by the Suspension Control Module on vehicles equipped with Real Time Damping (RTD), to calculate lateral acceleration. When the control module detects lateral acceleration is occurring less current is commanded to the Electronic Variable Orifice (EVO) solenoid. This increases steering assist during abrupt driving maneuvers.

NOTE: The BCM/ESC stores the DTCs scan tool data and special functions. However, the scan tool menu to access variable effort steering is located in chassis.

Conditions for Running the DTC

1. The ignition is ON.
2. No battery voltage malfunctions are present.

Conditions for Setting the DTC

A short to ground, short to voltage, or an open in the signal 1, or signal 2 circuits.

Action Taken When the DTC Sets

1. The EVO outputs will be disabled for the remainder of the ignition cycle.
2. DTC C0470 will be set if a malfunction is present on signal 1 circuit.
3. DTC C0506 will be set if a malfunction is present on signal 2 circuit.
4. The IPC message center displays the SERVICE STABILITY SYSTEM message.

Conditions for Clearing the DTC

1. A current DTC will clear after next consecutive ignition cycle with no malfunction present.
2. A history DTC will clear after 100 consecutive malfunction free ignition cycles.
3. Using the scan tool

The steering wheel position sensor is a 0-5 volt device which is used to sense steering wheel position and turning speed. The valid signal voltage range of the sensor is 0.35-4.75 volts. The signal voltage will increase or decrease within the valid voltage range as the steering wheel is turned. The Body Control Module (BCM) monitors the steering wheel position sensor signal voltage and uses this data to calculate lateral acceleration. When the BCM detects lateral acceleration is occurring less current is commanded to the Electronic Variable Orifice (EVO) Solenoid which increases steering assist during abrupt driving maneuvers.

NOTE: The BCM/ESC stores the DTCs scan tool data and special functions. However, the scan tool menu to access variable effort steering is located in chassis.

Anytime the key is in the on position.

A short to ground, short to voltage, or an open in the steering wheel position sensor signal circuit.

1. DTC C0472, or C0473 is stored in memory.
2. The EVO outputs will be disabled for the remainder of the ignition cycle.

1. A current DTC will clear when the malfunction is no longer present.
2. A history DTC will clear after 100 consecutive malfunction free ignition cycles.
3. Using the scan tool

The Body Control Module (BCM), or Electronic Suspension Control (ESC) Module, vehicles equipped with Real Time Damping (RTD), provides a pulse width modulated (PWM) supply circuit, and a control circuit to the Electronic Variable Orifice (EVO) solenoid. The supply circuit is used to regulate the current to the solenoid which controls the size of the power steering pump's output fluid orifice, depending on vehicle speed. This results in an increase or decrease in steering effort. The control circuit is used to disable the EVO outputs to provide full steering assist when a malfunction is detected.

NOTE: The BCM/ESC stores the DTCs scan tool data and special functions. However, the scan tool menu to access variable effort steering is located in chassis.

Vehicle speed greater than 8 km/h (5 mph).

EVO solenoid command greater than 5 percent PWM duty cycle.

1. EVO output PWM less than 10 percent duty cycle and EVO output current greater than 260 ma.
2. EVO output PWM greater than 94 percent duty cycle and EVO output current less than or equal to 360 ma.

1. DTC C0495 will be stored in memory.
2. The EVO outputs will be disabled for the remainder of the ignition cycle.

Conditions for Clearing the MIL/DTC

1. A current DTC will clear on next ignition cycle with no malfunction present.
2. A history DTC will clear after 100 consecutive malfunction free ignition cycles.
3. Using the scan tool

The Body Control Module (BCM), or Electronic Suspension Control (ESC) module, vehicles equipped with Real Time Damping (RTD), provides a pulse width modulated (PWM) supply circuit to the Electronic Variable Orifice (EVO) solenoid. The supply circuit is used to control the current to the EVO solenoid which regulates the size of the Power steering pump output fluid orifice. This causes an increase or decrease in steering effort depending on vehicle speed.

NOTE: The BCM/ESC stores the DTCs scan tool data and special functions. However, the scan tool menu to access variable effort steering is located in chassis.

Vehicle speed greater than 8 km/h (5 mph).

EVO solenoid command greater than 5 percent PWM duty cycle.

EVO output PWM greater than 5 percent duty cycle and EVO feed back voltage is less than battery voltage minus 4.0 volts.

1. DTC C0496 will be stored in memory on vehicles equipped W/ RTD.
2. DTC C0498 and C0499 will be stored in memory on vehicles W/O RTD.
3. The EVO outputs will be disabled for the remainder of the ignition cycle.

1. A current DTC will clear when malfunction is no longer present.
2. A history DTC will clear after 100 consecutive malfunction free ignition cycles.
3. Using the scan tool

The Body Control Module (BCM), or Electronic Suspension Control (ESC) module, vehicles equipped with Real Time Damping (RTD), provides a return or control circuit to the Electronic Variable Orifice (EVO) solenoid when the ignition is turned ON. This circuit is used by the control module to disable the EVO solenoid outputs when a fault is detected to provide full steering assist.

NOTE: The BCM/ESC stores the DTCs scan tool data and special functions. However, the scan tool menu to access variable effort steering is located in chassis.

Vehicle speed greater than 8 km/h (5 mph).

EVO solenoid command greater than 5 percent PWM duty cycle.

A short to ground, short to voltage, or an open in the EVO solenoid control circuit.

1. DTC C0501 will be stored in memory on vehicles W/ RTD.
2. DTC C0503 and C0504 will be stored in memory on vehicles W/O RTD.
3. The EVO solenoid outputs are disabled for the remainder of the ignition cycle.

1. A current DTC will clear after the malfunction is no longer present.
2. A history DTC will clear after 100 consecutive malfunction free ignition cycles.
3. Using the scan tool

The steering wheel position sensor is a 0-5 volt device used by the Electronic Suspension Control (ESC) module to sense steering wheel position and turning speed. The valid voltage range for the sensor is 0.35-4.75 volts. The output, or signal voltage increases and decreases within the valid voltage range as the steering wheel is turned. The ESC module monitors the two signal voltage values from the steering wheel position sensor, signal 1, and signal 2 circuits. These two signal voltage values should be aligned or synchronized with each other and in the valid voltage range.

NOTE: The BCM/ESC stores the DTCs scan tool data and special functions. However, the scan tool menu to access variable effort steering is located in chassis.

1. Battery voltage is 11-14 volts.
2. The ignition is ON.

Signal 1 and signal 2 offset greater than 16 degrees for 2 seconds.

1. DTC C0521 is stored in memory.
2. The EVO outputs are disabled.
3. The Electronic Brake Control Module (EBCM) may turn on the SERVICE STABILITY SYSTEM message in the IPC message center.

1. A current DTC will clear when the malfunction is no longer present for 10 seconds.
2. A history DTC will clear after 100 consecutive malfunction free ignition cycles.
3. Using the scan tool