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ing/air-conditioning system. The vacuum reservoir VEHICLE SPEED SENSOR (SPEED CONTROL DESCRIPTION The Vehicle Speed Sensor (VSS) is mounted to an adapter near the transmission output shaft. The sen- OPERATION The VSS is a pulse generator. The VSS pulse sig- nal to the speedometer/odometer is monitored by the DIAGNOSIS AND TESTING ROAD TEST Perform a vehicle road test to verify reports of speed control system malfunction. The road test Flutter in the speedometer indicates a problem which might cause surging in the speed control sys- If a road test verifies a system problem and the speedometer operates properly, check for: • A Diagnostic Trouble Code (DTC). If a DTC exists, conduct tests per the Powertrain Diagnostic • A misadjusted brake (stop) lamp switch. This could also cause an intermittent problem. • Loose, damaged or corroded electrical connec- tions at the servo. Corrosion should be removed from • Leaking vacuum reservoir. • Loose or leaking vacuum hoses or connections. • Defective one-way vacuum check valve. • Secure attachment of both ends of the speed con- trol servo cable. • Smooth operation of throttle linkage and throttle body air valve. • Failed speed control servo. Do the servo vacuum test. CAUTION: When test probing for voltage or conti- VACUUM SUPPLY TEST (1) Disconnect vacuum hose at speed control servo and install a vacuum gauge into the disconnected (2) Start engine and observe gauge at idle. Vac- uum gauge should read at least ten inches of mer- (3) If vacuum is less than ten inches of mercury, determine source of leak. Check vacuum line to (4) If vacuum line to engine is not leaking, check for leak at vacuum reservoir. To locate and gain (5) Verify operation of one-way check valve and check it for leaks. (a) Locate one-way check valve. The valve is located in vacuum line between vacuum reservoir (b) Connect a hand-operated vacuum pump to reservoir end of check valve. Apply vacuum. Vac- (c) Connect a hand-operated vacuum pump to vacuum source end of check valve. Apply vacuum. 8H - 4 SPEED CONTROL SYSTEM XJ DESCRIPTION AND OPERATION (Continued) |