GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide



Some models covered by this guide may be equipped with a Supplemental Inflatable Restraint (SIR), which uses an air bag. Whenever working near any of the SIR components, such as the impact sensors, the air bag module, steering column and instrument panel, disable the SIR, as described in this section.

Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions. However, steep grades up or down may cause variations in the selected speeds. The cruise control system has the capability to cruise, resume speed, accelerate, tap-up and tap-down. The main parts of the cruise control system are the turn signal and multifunction switch, the cruise control module, the cruise control cable, the vehicle speed sensor, the cruise control release switch and the stoplamp switch.

On vehicles equipped with the 3.1L (LG6) engine, cruise control functions are controlled by a cruise control module mounted under the I/P. On vehicles equipped with the 3800 (L27) engine, cruise control functions are controlled by the powertrain control module (PCM).

The cruise control system, on vehicles equipped with a 3.4L engine, uses a cruise control module to obtain and hold any desired vehicle cruise speed above a minimum speed of 40 km/h (25mph).

The cruise control system uses vacuum to operate a throttle servo unit. The servo unit maintains the desired vehicle speed by trapping vacuum at the proper servo position. The control module monitors vehicle speed and servo position and operates the vacuum and vent valves in the servo to maintain desired speed. The control module contains a low speed limit, which prevents system engagement below a minimum speed of about 25 mph. Operation of the control module is achieved with mode control switches located in the end of the turn signal lever. Two release switches are provided to disengage the system. An electrical release switch mounted on the brake pedal bracket disengages the system electrically when the brake pedal is depressed. A vacuum release valve, mounted on the brake pedal bracket, vents the trapped vacuum in the servo to atmosphere when the brake pedal is depressed, allowing the servo unit to quickly return the throttle to idle position.

See Figures 1 and 2

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Fig. Fig. 1: Example of the brake/stoplight switches mounted on the pedal bracket

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Fig. Fig. 2: Cruise Control Troubleshooting