Question about 2003 Jeep Grand Cherokee
I've only seen Cruise Controls have 1 or possibly 2 wiring problems by design.
Usually the Cruise Control Servo Unit itself if pretty darn dependable, and will outlast most everything else on the SUV/car.
The most common problem is usually a BAD GROUND wire at the CC Servo Unit itself, which is located under the hood and usually where it's mounted off to the drivers side at or near the engine firewall, or else up front nearest the battery box.
The other wiring problem might be a bad connector or dirty connection point from where the wiring harness is run into and under the steering column. That connector can be seen from under the dash area and checked pretty easily with a DVM for proper function.
With either an automatic transmission or clutch driven model there is one other "safety disengage switch" located on either the clutch pedal or else the brake pedal, and this switch (if it's not positioned properly, or defective - as in OPEN) will kill the +12-volt battery POWER going to the CC Servo Unit itself. The CC light may be ON, but there still won't be any battery power to the CC Servo Unit, causing it not to set.
On all newer generation CC units the vehicle "angle" or attitude sensor, and drive shaft VCO pickup sensor design were dropped, and instead the monitored engine speed is now taken directly from the engine's Black Box computer and used as the VCO reference. If this VCO signal is missing then the CC Servo Unit will not engage as well.
If the CC Servo Unit uses a vacuum line feed you'll need to check that as well to make sure the hose is intact and it's making a good snug connection.
If all these points show to be good - then the CC Servo Unit itself is bad and needs to be replaced. Make sure you troubleshoot everything else above first as the CC Servo Unit is no doubt pretty pricey in cost, and may not be bad at all.
Hope this solves your problem.
Posted on Aug 10, 2008
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