Intermittent Service Ride Control

magv4 · October 14, 2006

I have a stock 2001 Chevy Suburban 2500 6.0L (100,000 miles). The Service Ride Control message displays on cold days (below 50), but not on warm days.

Where should I look first?

Also, I've read through some of these other threads and I'm confused about what AutoRide means and how it relates to load leveling?

Does it effect all four shocks? How often should I replace the shocks?

Thanks

GM-Tech · October 15, 2006

Here's how it all works. Replacing shocks on a guess is not really an option since the shocks are like $200-$300 EACH.

The system needs to be properly diagnosed to find the cause of the message. There is no doubt a code that will help to narrow down the area of concern.

Real Time Damping Description and Operation

The RTD system is bi-state real time damping, two corner rear leveling (if equipped), and a electronic variable orifice, (EVO) power steering system, (if equipped).

The RTD system consists of the following:

• Suspension Control Module

• Compressor/Leveling Module

- Pressure Sensor

- Exhaust Solenoid

• Compressor Motor Relay

• Steering Handwheel Speed/Position Sensor

• Electronic Variable Orifice (EVO) Solenoid

• Shock Solenoid Valves

• Position Sensors

The objective of the suspension control module is to provide ride and handling results that are superior to a passive damper system, both on and off road at all load conditions. The suspension control module monitors body-to-wheel height, vehicle speed, handwheel position/speed, lift/dive status and a driver tow/haul input switch status in real time and instantly selects a "normal" or "firm" mode. This is done for each of the front and rear shock absorbers in order to adjust the vehicle for specific road and driving conditions.

The suspension control module will use the rear body-to-wheel displacements and vehicle speed inputs to keep the rear trim height of the vehicle at its desired level. This is done to optimize suspension geometry, headlight aiming, ride travel and keep the vehicle visually level. The system utilizes the compressor motor relay and the compressor/leveling module which contains the exhaust solenoid, pressure sensor and compressor motor. The vehicles's rear leveling compressor motor is switched ON and OFF via a compressor motor relay which is controlled by the suspension control module. The suspension control module provides a switched path to ground whenever compressor activity is required. The suspension control module supplies 5 volts to the RTD air pressure sensor. The pressure sensor uses this reference voltage to produce an analog output of approximately 0.15 to 4.85 volts. The signal voltage is a reference of the air pressure in the rear leveling system. The exhaust solenoid valve is switched ON and OFF via the suspension control module. The suspension control module provides a switched path to ground whenever the exhaust "head relief" sequence occurs at compressor start-up (If system pressure is lower than 10 psi).

The suspension control module also uses the steering handwheel position/speed sensor and vehicle speed inputs to control a power steering effort control valve. The suspension control module varies the steering assist by adjusting the current flow through the electronic variable orifice (EVO) solenoid control circuits. The amount of steering assist is dependent upon vehicle speed and input from the steering handwheel position/speed sensor. As the vehicle speed increases, the steering assist decreases and the driver effort increases. As the vehicle speed decreases, the steering assist increases and the driver effort decreases.

The shock solenoid valve is driven ON and OFF by the suspension control module. To activate the solenoid, it is initially subjected to full battery voltage for a short period of time. Once the solenoid is pulled-in, the supply voltage is pulse width modulated (PWM). The amount the shock solenoid valve is activated is based on inputs from the driver Tow/Haul switch, road inputs and the PCM. The suspension control module provides a common ground (low reference) for all 4 of the shock solenoid valves.

The suspension control module provides a common regulated voltage of approximately 5 volts to all four of the (body-to-wheel) position sensors, RTD air pressure sensor and the steering handwheel position/speed sensor. The suspension control module receives VSS from the PCM and over the class 2 circuit. The position sensors provide an analog signal voltage between 0.5 and 4.5 volts to the suspension control module. This signal voltage represents the wheel's position relative to the body. The suspension control module provides a 5 volt reference and a low reference to the position sensors.

blue dave · September 7, 2009

Wow! That is a most excellent description of the system. I am troubleshooting the stystem on my 2002 Yukon XL Denali and I need to know where the suspension control module and the automatic level control relay are located. Can anybody tell me?