Hydraulic System Service Conditions
FIG. 4 - RANGES FOR RIDE HEIGHT "H":
Rear Strut Knock
Rear strut knock is usually caused by a discharged rear suspension, not defective parts. Over time, the rear suspension may become discharged through the trapped line pressure valve causing the rear of the vehicle to lower. Up leveling will not activate unless the vehicle is operated with an adequate load (Fig. 4). Refer to SYSTEM TESTING AND REPAIR PROCEDURES.
Rear Suspension Groan
An extended "groan" noise made during down leveling is due to the design of the original down solenoid valve. The valve design has been revised and is available through Zone Parts Department (CBC 9700). Refer to Technical Bulletin section 66, number 9 for solenoid valve replacement.
Charge Solenoid Valve Grunt (1988 and 1989 models only)
A brief "grunt" noise may be produced by the charge solenoid valve (after brake applications) when the brake accumulator recharges. A revised valve (CBC 9701) was introduced during the 1989 model year at VIN 572952 and is available through Zone Parts Departments. Refer to Technical Bulletin section 66, number 9 for solenoid valve replacement.
NOTE: The new valve may still produce a noise in hot weather; this is normal.
Rear Strut Leakage
A trace of oil around the strut shaft boot is normal and does not indicate rear strut failure. External fluid leakage (resulting in oil on the strut shaft boot and lower housing) should be investigated and corrected.
SYSTEM TESTING AND REPAIR PROCEDURES
If rear suspension knock occurs, first reset the trapped line pressure and road test the vehicle. To reset the pressure, the system must be activated to the "up" condition (with the vehicle resting on its wheels), by either disconnecting the level sensor link rod and raising it manually or loading the vehicle with at least 600 lbs. at the rear axle. In both cases the engine should be held at a fast idle for at least one minute. The link rod should then be reinstalled or the vehicle unloaded. If suspension knock has been eliminated, the vehicle should be roadtested again after 24 hours.
If trapped line pressure is lost within 24 hours and knocking reoccurs, it is necessary to replace the down solenoid valve and the up leveling non-return valve. For solenoid valve replacement, refer to Technical Bulletin section 66, number 9.
If rear strut knocking occurs a number of weeks after the suspension has been set, the trapped line pressure should be reset as previously described. No other work should be performed at this time.
If no "up" leveling occurs, first ensure that there is no "Circuit 3" failure warning (indicating a failed fuse). Use the following electrical pre-tests to determine if an electrical fault exists.
Electrical Pre-Tests
Refer to the Power Hydraulic Diagram in the Sedan Range Electrical Guide
^ Disconnect the yellow PM4 connector at the solenoid valve block, RS19.
^ With a DVOM set to the Ohms scale, test the resistance through each valve solenoid winding. The resistance should be 27 to 32 ohms. Test the resistance between each solenoid winding and the valve block casting. An open circuit should exist.
^ If the solenoid valve fails the previous test, replace the affected part. For solenoid valve replacement, refer to Technical Bulletin section 66, number 9.
^ Reconnect the PM4 connector, RS19.
^ Set the DVOM to the D.C. Volts scale. Connect the negative test lead to a chassis ground.
^ With the ignition switched off, there should be battery voltage to the down solenoid, pin RS19-5.
^ Switch the ignition on. There should be battery voltage to the charge solenoid, pin RS19-1, and to the up solenoid, pin RS19-3.
^ Switch the ignition off. Disconnect and raise the ride level sensor link 2-3 cm.
^ Start the engine and wait 30 seconds. The up solenoid signal wire, pin RS19-4 and the charge solenoid signal wire, pin RS19-2, should be grounded (0 volts). Battery voltage indicates a fault. The down solenoid signal wire, PIN RS19-6, should have battery voltage. Low voltage indicates a fault.
^ Switch the ignition off. Lower the ride level sensor link to slightly below the attachment point at the lower control arm.
^ Switch the ignition on. The down solenoid signal wire, pin RS19-6, should be grounded, (low volts). Battery voltage indicates a fault.
^ The up solenoid signal wire, pin RS19-4, should have battery voltage. Low voltage indicates a fault.
^ Reconnect the ride level sensor link.
If the electrical pre-tests are passed, locate the problem by performing a power hydraulic pressure test. Refer to Technical Bulletin section 66, number 5.
If an electrical pre-test is failed, perform a JDS test to locate the fault.
"Low Brake Pressure" Warning (1988 and 1989 models only):
If there is a "Low Brake Pressure" warning on a 1988 or 1989 model vehicle, first ensure that there is no "Circuit 3" failure warning (indicating a failed fuse). Then perform a power hydraulic pressure test. Refer to Technical Bulletin section 66, number 5.