Does anyone happen to know the resistor values for the multiplexed cruise control buttons? Mine just works sometimes and other times it doesn't on various buttons, so I wanted to check all the resistors in the buttons to make sure those were all correct.

 

Did you check for any codes in the PCM for speed control? If there is codes,post them.

 

There's no codes, just sometimes the buttons work when it's cold, then when things heat up random ones stop working. I checked all the wiring and it all checks out, then I learned they multiplex the 5 buttons to work on 2 wires (1 ground and 1 signal) so I just wanted to make sure the resistors were still holding their valves correctly.

 

This maybe what you are looking for.
OPERATION
When speed control is selected by depressing the ON, OFF switch, the PCM allows a set speed to be stored in its RAM for speed control. To store a set speed, depress the SET switch while the vehicle is moving at a speed between approximately 35 and 85 mph. In order for the speed control to engage, the brakes cannot be applied, nor can the gear selector be indicating the transmission is in Park or Neutral.

The speed control can be disengaged manually by:
Stepping on the brake pedal
Depressing the OFF switch
Depressing the CANCEL switch.
The speed control can be disengaged also by any of the following conditions:
An indication of Park or Neutral
The VSS signal increases at a rate of 10 mph per second (indicates that the co-efficient of friction between the road surface and tires is extremely low)
Depressing the clutch pedal.
Excessive engine rpm (indicates that the transmission may be in a low gear)
The VSS signal decreases at a rate of 10 mph per second (indicates that the vehicle may have decelerated at an extremely high rate)
If the actual speed is not within 20 mph of the set speed
The previous disengagement conditions are programmed for added safety.
Once the speed control has been disengaged, depressing the ACCEL switch restores the vehicle to the target speed that was stored in the PCM's RAM.

NOTE: Depressing the OFF switch will erase the set speed stored in the PCM.

If, while the speed control is engaged, the driver wishes to increase vehicle speed, the PCM is programmed for an acceleration feature. With the ACCEL switch held closed, the vehicle accelerates slowly to the desired speed. The new target speed is stored in the PCM's RAM when the ACCEL switch is released. The PCM also has a "tap-up" feature in which vehicle speed increases at a rate of approximately 2 mph for each momentary switch activation of the ACCEL switch.

The PCM also provides a means to decelerate without disengaging speed control. To decelerate from an existing recorded target speed, depress and hold the COAST switch until the desired speed is reached. Then release the switch. The ON, OFF switch operates two components: the PCM's ON, OFF input, and the battery voltage to the brake switch, which powers the speed control servo.

Multiplexing
The PCM sends out 5 volts through a fixed resistor and monitors the voltage change between the fixed resistor and the switches. If none of the switches are depressed, the PCM will measure 5 volts at the sensor point (open circuit). If a switch with no resistor is closed, the PCM will measure 0 volts (grounded circuit). Now, if a resistor is added to a switch, then the PCM will measure some voltage proportional to the size of the resistor. By adding a different resistor to each switch, the PCM will see a different voltage depending on which switch is pushed.

Another resistor has been added to the 'at rest circuit' causing the PCM to never see 5 volts. This was done for diagnostic purposes. If the switch circuit should open (bad connection), then the PCM will see the 5 volts and know the circuit is bad. The PCM will then set an open circuit fault.

 

Ah, the multiplexing part shed some light on how it exactly works. I noticed the "at rest" resistor in there that didn't go to any buttons, with it removed the cruise control would not turn on unless you added some resistance in the circuit by holding down another button (accel or decel) at the same time, then releasing that button will cause the cruise light to go out.

So when the PCM sees 5 volts it turns off cruise and throws a code, that's good to know. It's just annoying to be driving to work on the highway and sometimes it works and when it doesn't, I have to put it in N, turn the key off, restart the engine, and it will work for maybe another 2 miles. It works fine forever when the outside temp is say 40 or under, anything above that and it will work for a few miles then the cruise light goes out.

I'm thinking a power surge or higher than 5v voltage something went through that 5v line and when someone pressed a cruise button it fried the resistor for it.

 

Ok so I have a similar problem...Mine: Would the multiplexing unit turn the whole cruse system off? I have a problem where as:

I will turn the cruise on light on dash comes on, but when I go to hit set it shuts the light off and never engages the cruise.

Other times the cruise will work and then after any where from 10-200 miles it will just shut the cruise system off.

Seems to act up less in the cold and no wetness? IDK I called the dealership I do a lot of business with and at the high end it would cost 520 to just replace the entire cruise system.

If anybody has any idea's let me know...BTW Thanks ahead of time and this is my 1st post so be nice please

 

For mine I just bought the factory service manuals to find out how to test these things and here's what I got from it. In the "powertrain diagnostic procedures" book under code P0579 it tells me the resistance for all the switches
Resume - 15,400 ohms
Cancel - 909 ohms
Decel - 2940 ohms
On/Off - 0 ohms (basically no resistor on this circuit, just completely closed when pressed)
Set - 6650 ohms
When I tested my switches these values varied by a few 100 ohms but that shouldn't be a problem as these values are widely spread apart. Plus engineers of this design also have to take into account resistor operation temperature and tolerances.
It looks like the there's a ground, then these resistors pass different valves from that ground to the PCM so all 5 buttons can be read with only using 2 wires (most likely to keep the clockspring simplified). Now it seems that the PCM is outputing 5volts on it's return signal line and grounding out this 5 volts with different switch vaules lowers the voltage and the PCM detects this. 0.43 volts looks to be the lowest possible voltage before setting the MIL light with code P0580 and a voltage of 4.8v or more will trip the P0581 code (remember there's a resistor added in line that's always always connected so the PCM wants to see less than 4.8 v but more than 4.7v return when no buttons are pressed)
Hope this helps.

 

Well I finally fixed the real problem with the cruise system after almost a year of getting fed up with it and it seems to be a common problem on these vehicles that a lot of people hint on but never fully explain.

Basically it's all in the brake switch circuit. I tested for power at the cruise control servo brake wire (which should be 12 volts with the brake not depressed) and there was a small amount of current there but not enough to activate the relays. The speed control servo has relays inside to control the throttle cable, these relays get power from the a circuit running through the brake switch, when you press the brake you open this circuit and the servo gets no power. Then the PCM just completes the ground path to these relays to activate them.
Hopefully others with this problem can check there first now and save a lot of time since from what I heard it's a common problem, just get a voltmeter/multimeter/test light in there and see if you got that 12v on the servo connector. Also since you got the multimeter out, check for good ground at all of the circuits ground pins.

I'll post pictures of the factory service manual wiring diagrams and connector pinouts with wire colors soon so this all makes sense.

 

Okay so what wire colors am I looking for? Also did you just run a new ground or was it the brake light switch then? If you have any pictures it would be awesome too!

 

Obviously I know black for ground...but what color is the brake supply?