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OPERATION The speed control electronic control circuitry is integrated into the Powertrain Control Module (PCM). The PCM speed control functions are moni- USE THE DRB SCAN TOOL TO REPROGRAM THE NEW PCM WITH THE VEHICLES ORIGI- VACUUM RESERVOIR The vacuum reservoir is located in the engine com- partment. OPERATION The reservoir stores engine vacuum in the reser- voir. When engine vacuum drops, as in climbing a VEHICLE SPEED AND DISTANCE OPERATION The 4 speed automatic Transmission Control Mod- ule (TCM) supplies the speed input to the PCM. The Vehicles with a 3 speed automatic or manual trans- mission have a Vehicle Speed Sensor (VSS) mounted ROAD TEST OPERATION 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 surge following a set and the speedometer operates properly see “Overshoot/ If a road test verifies an inoperative system, 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 or corroded electrical connections at the servo. Corrosion should be removed from electrical • Leaking vacuum reservoir. • Loose or leaking vacuum hoses or connections. • Defective one-way vacuum check valve. • Secure attachment at both ends of the speed control servo cable. • Smooth operation of throttle linkage and throttle body air valve. • Conduct electrical test at PCM. • Failed speed control servo. Do the servo vacuum test. CAUTION: When test probing for voltage or conti- CHECKING FOR DIAGNOSTIC CODES OPERATION When trying to verify a speed control system elec- tronic malfunction: Connect a DRB scan tool if avail- (1) A speed control malfunction may occur without a diagnostic code being indicated. For further information and usage of the DRB scan tool and a more complete list of Diagnostic Trouble JX VEHICLE SPEED CONTROL SYSTEM 8H - 5 DESCRIPTION AND OPERATION (Continued) |