Tempostat system components
Tempostat allows you to automatically maintain the selected cruising speed of the vehicle. The electric servomotor of the speed control system is located in the engine compartment and is connected by a cable to the throttle actuator lever. The main components of the system include an electronic control unit, switches for controlling the functioning of the tempostat, a sensor-switch for brake lights and a vehicle speed sensor (VSS) (refer to illustration above). Checking the individual functions of the system requires the use of special diagnostic equipment, and its implementation lies outside the qualifications of the average amateur mechanic. Below is a description of the procedures for only the most common checks that allow you to identify the causes of the most typical tempostat failures.
1. Find the tempostat fuse and check its condition (see Section Fuses - general information).
2. Ask an assistant to depress the foot brake pedal several times - the operation of the brake light sensor-switch that reacts to depressing the pedal should lead to the deactivation of the tempostat.
3. If the brake lights do not respond to pressing the pedal, find out the cause of the failure and repeat the test.
4. Visually assess the condition of the drive cable routed from the tempostat servomotor assembly to the throttle linkage. Replace damaged or worn cable.
5. The operation of the tempostat is based on the monitoring of signals from the vehicle speed sensor. VSS is built into the transmission, a description of the check of its correct functioning is given in the Chapter Engine management and emission control systems this guide. Assess the condition of the contact connections of the instrument cluster (see Section Removal and installation of a combination of devices).
6. Carry out a road test of the vehicle. If it was not possible to eliminate the malfunction of the tempostat during the corrections made, drive the car to a service station for a more detailed diagnosis of the system using special equipment.