Visual Inspection
Important: The visual inspection must be done carefully and thoroughly.
One of the most important checks, which must be performed before any diagnostic activities, is a careful visual inspection of suspected wiring and components. This can often lead to the correction of a problem without further action. Inspect the battery "green eye" to assure the battery is not discharged. Inspect all electrical circuits for pinches, cuts, and disconnects.
Basic Knowledge Required
Before attempting to diagnose the Continuously Variable Road Sensing Suspension (CVRSS) system, you must have a good understanding of electrical system basics and the use of testing tools. Without this basic knowledge, it will be difficult to use the diagnostic procedures detailed in this section.
| • | Basic Electrical Circuits -- You should understand the basic theory of electricity, series and parallel circuits, and voltage drops across series and parallel resistor systems. You should know the meaning of volts (voltage), amperes (current), and ohms (resistance). You should understand what happens in a circuit with an open wire or a wire shorted to ground or battery. You should be able to read and understand a wiring diagram. |
| • | Use of Circuit Testing Tools -- You should know how to use a Digital Voltmeter (DVM) to measure voltage, current, and resistance. Be aware that when DVM use is requested, the first terminal listed in the check is intended to be connected to the positive (usually red) DVM lead. You should know how to use jumper wires to test circuits. |
Computer System Service Precautions
The computer system is designed to withstand normal current draws associated with vehicle operation. However, care must be taken to avoid overloading any of these circuits. In testing for opens or shorts, do not ground or apply voltage to any of the circuits unless instructed to do so by the diagnostic procedures. These circuits should only be tested using a digital voltmeter if they remain connected to one of the computers. Power should never be removed or applied to one of the computers with the ignition switch in the ON position. Before removing or connecting battery cables, fuses, or connectors, always turn the ignition switch to the OFF position.
Leveling System Complaints
Various electrical and pneumatic fault conditions can prevent valid leveling system operations. Although some of the fault conditions cause storage of corresponding fault codes, none of them causes the SERVICE RIDE CONTROL message to be displayed.
Therefore, if a complaint of incorrect vehicle leveling operation occurs, always begin the diagnostic procedure by displaying fault codes and repairing any faults which are recorded. After all fault codes are addressed and cleared, if the leveling system continues to operate incorrectly or fails to operate, check for pneumatic and/or compressor module problems, as appropriate (refer to the Automatic Level Control Section).
Vehicle Ride Complaints
The CVRSS control module is able to detect the majority of electrical problems in the CVRSS suspension damping control system. All detectable faults cause the SERVICE RIDE CONTROL message to be displayed. Mechanical, hydraulic and pneumatic problems generally do not cause storage of fault codes. Additionally, it is important to note that the vehicle ride and handling characteristics are influenced by a number of factors, including tire inflation and leveling system operating pressure.
Therefore, if a complaint of harsh, soft, or inconsistent ride occurs, always begin the diagnostic procedure by displaying fault codes and repairing any system faults which are recorded (refer to Road Sensing Suspension Diagnostic System Check ). If the vehicle ride continues to be objectionable after all fault codes are addressed and cleared, check for problems in the following areas:
| • | Tire Pressure: Ensure that tire pressure is within the manufacturer's suggested guidelines. Overinflated tires are a very common cause of additional (undesirable) ride harshness |
| • | Leveling System Operating Pressure: Ensure that the leveling system is operating correctly and that the rear air sleeves contain at least the minimum retention pressure (refer to the Automatic Level Control Section) |
| • | Suspension Mechanical or Hydraulic Problems: Thoroughly inspect all suspension components for loose/broken mechanical connections, abnormal wear conditions, or fluid leakage, and repair as necessary (refer the Rear Suspension Section). |
Ignition Cycle Counting
The CVRSS control module employs a fault buffering approach known as Ignition Cycle Counting. This allows degraded mode activation to occur whenever a fault condition is present, but requires a given fault to be active for several ignition cycles before a corresponding fault code is stored or the SERVICE RIDE CONTROL display is activated. This additional buffering is intended to reduce the occurrence of nuisance codes caused by intermittent problems.
It is important to note that intermittent fault conditions, although not causing SERVICE RIDE CONTROL activation or fault code storage, do cause activation of one or more system degraded modes. For example, an intermittent position sensor input fault causes the system to intermittently enter a speed-dependent damping mode in which the sensor information is not used; however, no SERVICE RIDE CONTROL message is displayed, nor a fault code stored, until the fault condition has been continually present for several ignition cycles.
Important: If a vehicle is brought in with a complaint about ride quality or leveling system operation, but no CVRSS fault codes are stored, always perform the following steps before concluding that no electrical fault is present.
- Clear faults codes. (This will disable the Ignition Cycle Counting function for the current ignition cycle and thus allows any intermittent or new fault conditions which are present to result in fault codes).
- Drive the vehicle above 50 MPH for at least 20 seconds.
- Read fault codes. If fault codes are now present, refer to the corresponding fault diagnostics.
If there are still no fault codes stored, then there are no electrical faults apparent in the system. Investigate mechanical causes for the complaint.
