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Electronic Cruise Control Page 4
Troubleshooting
This page will help in fixing only the most common causes of the cruise control failing to engage. This includes fail to engage, or not holding set speed or surging.
WARNING!!
Absolutely do not bypass the electrical terminal to the brake switch AND/OR the vacuum line to the TCC lockup switch! These two functions are there to insure the cruise control will disengage. Unless it is to test for a bad connection, and only then while the vehicle is in park and parking brake set. Always reconnect back to original set up after testing and before driving vehicle. Failure to do this will result in loss of control, possible property damage, serious injury or death.
Failure to engage:
Most common is the switch where the vacuum line hooks to. If it is not properly adjusted, the cruise module will not have the vacuum to operate. If this is the case and you are using a OD transmission, you will notice that the lock up will not operate also, because this is where the TCC switch (purple and pink/black wires) hook to.
Check the adjustment, the best way to do this is to depress the brake pedal, and push the switch all the way in its holder. When you release the pedal, the adjustment will take place automatically. If the switch is real loose in the holder, pull the metal retainer out of the holder and slightly bend the tab in the inside to hold the cruise/TCC switch more securely. Reinstall and repeat the adjustment procedure. Be sure to install the vacuum line to the switch.
With the switch in place and adjusted properly, pull the large vacuum line off the servo and try to blow through it. You should not be able to. If there is a problem here, pull the hose off the switch and plug it, install your hand vacuum pump to the other end and pull a vacuum, there should be n loss in vacuum. If the gauge shows there is a leak, make sure plug is secure, repeat test, if it still leaking, you have a bad hose, replace it.
Be sure to also check the smaller line to the servo for leaks. Put your vacuum pump on each of the two vacuum line ports and pull a vacuum. There should be no leaks here. If there is, replace the servo.
Check the wiring connections, especially on the cruise control switch.
Check for power with the ignition key "on" at the brn/wht wire at the 4 way connector. If there is no power, see if the fuse is blown. if so, investigate as to why there is a problem, and correct it before you install a new fuse. You must have power here for the rest of the system.
Check the integrity of the wiring connections to the switch, using this chart above a a continuity tester. Check your results twice to insure you are getting the proper readings. Check the rest of the wiring harness for the same good continuity through the terminal ends.
Make sure that the VSS is functioning, that there is power on the pnk/blk wire with ignition key "on", that the black is wire is securely grounded, and that the brown or red wire that is the signal from the VSS is sending a signal to the cruise module. You can hook a lead from a analog voltmeter to this signal (brown or red) wire and ground the other VOM lead, then drive the vehicle while observing the needle, it should swing back and forth from 0 to 12V, as the reflector on the speedometer is activating the VSS module. If the needle does not move, and you have confirm you have power to the VSS module, and you have a functioning speedometer, you'll have to replace the VSS module. As you pull the instrument panel to pull the VSS from the speedometer, be sure the reflector is clean.
The VSS works by using the reflections of the reflectors located in speedometer head. There are two of these 180 degrees from each other. As the speedometer cable spins, the infrared emitter led sends a beam to the reflectors, the "flashing" is detected by the infrared detector led. This pulsing sends the signal which is converted by the VSS module into a analog voltage signal to the ecm and the cruise module, which is read by these modules as a representation of speed in mph. It is important that this functions properly as it affects several functions such as torque converter lock up and the performance related functions such as egr, fuel injection calculations etc.
Another electrical problem could be in the servo unit. This can be checked with a ohmmeter between the terminals "A" and "B" and between terminals "D" and "E". Any very low or excessively high reading indicates a open or short in the solenoid coil windings.
If all the electrical system, including the servo checks out okay, and the cruise still won't function, the cruise module itself is probably bad.
Cruise "sets" but will not "resume" or "accel":
If you have to depress the brake pedal to slow down, but you have not turned the cruise switch to "off" position, and want to resume your cruise speed. If the vehicle won't resume, the two most likely causes are a faulty cruise switch or module. If the switch checks out okay, the module is probably faulty. Be sure to check your wiring connections first.
The accel feature works when the button is held to the right for more than a second. The module interprets this as a command to accelerate. If this function will not work even though normal cruise function works, check the switch and all the wiring connections, replace the module if everything else is okay.
Speed "surging" while in cruise.
The likely cause is a binding speedometer cable which affects the operation of the VSS, sending a erratic signal to ecm and cruise module. If your speedometer is erratic along with a problem with the lock up converter seeming to "jump", you need to check and/or replace your speedometer cable. A faulty speedometer head can cause this problem. Also a vacuum leak can cause this problem. Also check your wiring connections.
Cruise will not engage below 35 mph.
This is a safety feature, which cannot be defeated.