AutoFocus: Cruising along
Mitsubishi’s vacuum pump-operated Auto-Cruise Control system is found on many makes and models covering a wide range of years.
The system is turned on and off by depressing the auto cruise main switch. This will cause the cruise control indicator light to illuminate on the instrument cluster. Once the vehicle is above approximately 25 mph, the switch can be moved to the “Set” position. If the driver wants to increase speed, the switch can be moved to the “ACC” position.
The system incorporates a “tap-up” feature which allows the switch to be moved momentarily and released.
This will cause an increase in speed of 1 mph. To slow down, the driver can perform a similar function by holding down the “Coast” button or momentarily performing the “tap-down” feature which slows the vehicle by increments of 1 mph.
As with most other cruise control systems, the system can be disabled by applying the brakes. Once the “Set” speed is memorized by the Auto-Cruise Electronic Control Unit (ECU), the system will operate until one of the following conditions exists:
* the cancel switch is activated,
* the brake pedal is pressed,
* the automatic transmission is in Park or Neutral,
* the clutch is disengaged (manual transmission),
* the vehicle speed is below 25 mph,
* the speed drops to 9 mph below the “Set” speed,
* there is a sharp increase in vehicle speed, or the “Set” speed is not achieved within 10 seconds.
If the cruise control is cancelled, the “Set” speed is retained in memory. Once again, like other systems, if the driver moves the switch to the “ACC/RES” the vehicle will resume to the “Set” vehicle speed.
So far there is probably nothing too new about this system. What happens behind the scenes is where there are some differences.
First of all, the components used include the following: vacuum pump assembly, vacuum actuator on the throttle body and Auto-Cruise ECU. The system is capable of setting a limited number of fault codes. To check the Auto-Cruise control system for fault codes, use the following procedure:
1) Turn the ignition switch to the “ON” position while holding the Auto-Cruise control switch in the “SET” position (position is down).
2) Then within one second, move the cruise control switch up to the “ACC/RES” position.
3) The fault codes will be flashed out using the “Cruise” control indicator light on the instrument cluster. If there is a fault code stored, there will be a long flash followed by a series of short flashes. The long flash is the first digit. The short flashes are the second digit. For example, one long flash followed by four short flashes is a code 14.
Incidentally, the system also has a “normal” flash (a continuously flashing “Cruise” indicator), which also means no codes. There will be no distinction between long flashes and short flashes. It will flash as long as the key is turned on. There are code charts for the limited codes that are available.
The vacuum pump assembly can be tested using jumper wires. There is one common battery voltage feed, which comes from the brake switch and Auto-Cruise ECU. Then, there are three control wires: vacuum pump ground control, Control solenoid ground control, and Release solenoid ground control.
Grounding the vacuum pump control wire will cause the vacuum pump to run. When the Control and the Release solenoids are grounded at the same time, along with the vacuum pump, the vacuum will build and then flow to the actuator on the throttle body. Once the actuator has the vacuum signal to it, it will pull a connected rod to open the throttle. Make sure the engine is turned off for this test!
Here are a few quick tidbits of helpful information:
* Auto-Cruise Switch approximate voltages — all of the switches are momentary contact. In order to read the voltage you must hold the switch “On.”
* 4.43 volts at rest
* 8.18 volts while pushing in the On/Off button
* 1.48 volts when holding the Coast/Set button
* 2.98 volts when holding the ACC/Resume button
* The vacuum pump is capable of about 15 inches of vacuum. If the actuator is good, it will be able to open the throttle all the way to wide open when running the vacuum pump and solenoids with jumper wires.
* The vacuum actuator should hold vacuum.
Hopefully this will help if you happen to get one of these cruise control systems in your shop.
Service data provided by Greg Montero of Identifix Inc. For more information, call (800) 997-1674 or visit the company’s Web site at www.identifix.com.