Cruise control only works momentarily

[Christopher Garretson]

Hello,

I have a 97' 4.0 4x4 5 speed xlt Ranger.

The cruise control on my truck only works momentarily. I press the set/acc button and the dash light "cruise set" flashes but turns off instantly. I have run continuity tests on most all of my sensors and checked the resistance of my steering wheel buttons. I don't understand why the light shuts off immediately. It's as if the system allows it to engage but a sensor quickly shuts it off. I don't know if the motor is actually pulling on the throttle body cable, but I am looking to test that today.

Any thoughts?

 

[RonD]

Welcome to TRS

1997 Cruise wiring below

First question is does your speedometer work, if not then that's the problem

The Vacuum actuator module, with the cable, in the engine bay is also the cruise control "amplifier"(electronic part)
It is powering on because light comes on

There are only 2 wires that come from the steering wheels buttons, there is no connection between the wires unless a button is pressed, so if a button is "stuck" a connection would exist and cruise would shut off

Key off, test the two wires at the unplugged amplifier's 10 pin connector, while someone pushes the buttons see if OHMs change as shown

 

[Christopher Garretson]

RonD,

Thank you for the diagram.

Yes the speedometer works.

So because my dashboard light is flashing momentarily, you're saying that the cruise control "amplifier" can't be the issue?

I tested the ohms at pins 5 and 6 of the unplugged amplifiers 10 pin connector while someone pressed the buttons:

OFF should be 0 ohms, and it works
ON should be 1000 ohms, but it doesn't work
RESUME should be 2200 ohms, but it doesn't work
SET/ACCEL should be 680 ohms, but it doesn't work
COAST should be 120 ohms, and it works

I soldered resistors together to give me the values I need for the three buttons that don't work. Then I plugged them in, in the correct order, to simulate ON, and then SET, and then RESUME. The same thing happens: only after pressing ON, all three buttons cause the dash light to flash momentarily.

 

[RonD]

It certainly could be the amplifier, most electronics have a start up self test, so if that failed then it would shut off
I was just saying it wasn't blown fuse or bad ground, amplifier is powering up

But if it wasn't getting correct signal from buttons, brake/clutch or pressure switch it would also shut off

Generally speaking the mechanical parts that are used the most are what wears out, electronic parts do fail, they are just usually the least likely to fail

 

[Christopher Garretson]

Ok, Thank you