Engine/Transmission (1994 - 1998) Cruise control not working; 1996 12v auto trans

[Solar1]

Hello folks,
I have a problem with the cruise control.
I just had a new trans installed, but cruise was not working previous to the install.

The steering wheel light comes on, but not response from cruise unit.

Question: Is the cruise control managed by the computer unit?
The reason I ask is that do to ongoing ABS brake control issue, the brake light and abs light are both on.
Could it be that due to brake issues, the cruise wont activate?

I can also note, (if it matters) that installing a new TPS has not helped.

Any test/troubleshoot procedures would be appreciated.
Thanks!

 

[mwilson]

Sounds like a vacuum leak to me. Cruise vacuum line is notorious for rotting out under the forward edge of the left side battery tray. Borrow or buy a hand held Mity Vac tool. Then you can create vacuum with out running the truck. Then fix each leak as you find. Most likely more than one. That may also be the issue with.the warning lights. I believe the 96 has a switch with a vacuum line going to it on the left inner fender between the battery and the firewall. My 94 had that. I believe that switch/sender is on any truck with a vacuum booster. Newer 2nd Gen trucks came with hydraulic assist brakes.

 

[Solar1]

Sounds like a vacuum leak to me. Cruise vacuum line is notorious for rotting out under the forward edge of the left side battery tray. Borrow or buy a hand held Mity Vac tool. Then you can create vacuum with out running the truck. Then fix each leak as you find. Most likely more than one. That may also be the issue with.the warning lights. I believe the 96 has a switch with a vacuum line going to it on the left inner fender between the battery and the firewall. My 94 had that. I believe that switch/sender is on any truck with a vacuum booster. Newer 2nd Gen trucks came with hydraulic assist brakes.

Thanks mwilson,
I never thought about the vacuum line.
I've got a hand vac pump as well as a robinair hvac vac pump.

You just may be right, as I've replaced almost everything on the truck except the vacuum lines.
At 380K miles, there's bound to be some leaks!
I'll check it out tomorrow and report back my findings...Thanks!

 

[Solar1]

Well folks, it appears I have decent vacuum at the cruise unit (i think it's called a servo?)
Before I dive too deep and replace it, any other ideas?
Thanks

 

[BigPapa]

The brake light switch has been my most common culprit. Some folks say you can adjust them, but I've never been able to so I just bought new ones.

To test it, while you're driving, lift up on the brake pedal with your foot and try to set the cruise.

 

[Solar1]

The brake light switch has been my most common culprit. Some folks say you can adjust them, but I've never been able to so I just bought new ones.

To test it, while you're driving, lift up on the brake pedal with your foot and try to set the cruise.

thanks big papa!

 

[Dutch & Di]

Check the cruise control vacuum unit under the left side battery. Ours stopped working way back when and we found the battery had leaked just enough to eat a hole in the vacuum assembly. We had it replaced at a dealer and Dutch made a servo protector shield {out of a piece of aluminum} so that it couldn't happen again. Hope it helps. Hugs, Di

 

[GAmes]

If that fails, troubleshooting is in the factory service manual. I prefer the paper manual.

http://www.genosgarage.com/product/dfsm96-cd/dodgeram-factory-service-manuals

http://www.genosgarage.com/product/dfsm96-print/dodgeram-factory-service-manuals

 

[flexyxj]

I had this problem recently on my '96. Everything tested good. I had the switch on the steering wheel replaced and that cured the problem.

 

[Solar1]

I checked vacuum (good), brake switch (good).
Checked steering wheel switch and all good except between pin 1 and 2, supposed to be 806 ohms with no switch depressed.
There is no reading (open). The weird thing is that I pulled 3 switches from salvage yard and all 3 plus my switch present the same condition (between 1 and 2). Can all 4 switches be bad or is there a error (or part spec change) in the service manual?

My next step is to check the pin readings at the servo.
(I need to pull the battery because it's way too tight trying to work around it.)

Can anyone confirm the switch readings (between pin 1 and 2) as OK?
thanks

 

[GAmes]

I'll look at my manual tomorrow to see if the same requirement is on a '97. In the mean time, To check the servo wiring I cut a plug out of a wreck and used the pigtail to make the checks rather than pull the battery. You might want to anyway. This is a past thread I had. http://www.cumminsforum.com/forum/9...-anybody-have-serviceable-clock-spring-2.html

 

[fest3er]

Given the connector resembles:

+------------+
+ -  -  -  - +
+   +
+   +
+------------+
   | |

the hypens inside the 'box' are the pins, number 4 to 1 (left to right).

• Pin 1: vacuum, increase speed
• Pin 2: vent, decrease speed
• Pin 3: +12VDC
• Pin 4: ground

1. Jumper +12VDC and ground to pins 3 and 4, respectively.
2. Start engine, leave in neutral or park.
3. Momentarily (and I *do* mean momentarily: a millisecond is too long) jumper pin one to ground. The engine speed should increase. Do it a couple times to get the engine up to maybe 2500 RPM.
4. Momentarily jumper pin 2 to ground. The engine speed should decrease. Do it a couple times.
5. Disconnect pin 3 to return to idle.

My CC hasn't worked in years. I did this to verify that the servo was in good working order. My problem is elsewhere. Prolly in the PCM, possibly in the steering wheel (the switches connect different resistances to the PCM which is how the PCM know which switch was pressed)

 

[GAmes]

I checked vacuum (good), brake switch (good).
Checked steering wheel switch and all good except between pin 1 and 2, supposed to be 806 ohms with no switch depressed.
There is no reading (open). The weird thing is that I pulled 3 switches from salvage yard and all 3 plus my switch present the same condition (between 1 and 2). Can all 4 switches be bad or is there a error (or part spec change) in the service manual?

My next step is to check the pin readings at the servo.
(I need to pull the battery because it's way too tight trying to work around it.)

Can anyone confirm the switch readings (between pin 1 and 2) as OK?
thanks

My '97 manual only has you testing resistance between pins 2 & 3, not 1 & 2. I am under the impression that a '96 switch assy is the same design as a '97.

 

[LandShark]

Cruise activation is controlled by the computer. It will not work if the brake light is on. Not sure if the same applies to the ABS light, but I would think so. You need to resolve your brake issues first.

 

[fest3er]

Cruise activation is controlled by the computer. It will not work if the brake light is on. Not sure if the same applies to the ABS light, but I would think so. You need to resolve your brake issues first.

Technically, cruise control won't work if the switch at the brake pedal doesn't send +12VDC power to the servo. This is why CC disengages when you step on the brake: the switch opens.

 

[Texis]

I finally paid $49 bucks on EBAY for a new surplus MOPAR servo (on a guess) and that did the trick for mine.. cruise is working fine now. I had gone through most of the other traps and nothing was helping. If all else fails, get a new servo and that may cure yours as well.

It will not work if the brake light is on

It depends on "why" the brake light is on. My brake light is on due to ABS issues (I think), but cruise works fine. The brake pedal switch has contacts for tail lights, ABS and cruise. So I believe it would depend on why the brake light is on as to whether cruise will function or not.

BTW the auto parts houses don't sell the servos. I suppose that's a testament to the reliability of the units. If this one last 20 years I'll be satisfied.

Good luck with yours.

 

[GAmes]

It will not work if the brake light is on.

Just to avoid confusion, the brake light switch under the pedal activates the rear brake lights, not the brake light in the dash. It's other job is to disengage cruise if it is being used.

 

[Bob4x4]

A drb 3 would be the best way to check the system.You have already checked the easy stuff

 

[Solar1]

Hello folks,
I have tested vacuum (great, 25" at servo and elsewhere)
Tested servo wiring at connector per the 96 service manual. Checks OK
Checked servo itself per the manual. Checks OK. (I will check using procedure from Neal. (Thanks Neal.)

I believe the problem lies in the low vacuum sensor as detailed on other TDR threads and elsewhere.
The vac port was broke off but repaired some time ago and no vac leaks. I just closely examined it and found a split in the potting material with green corrosion coming out. So, I'm assuming it shot.
As noted in other threads, I have had no luck finding a replacement, new or used.

In researching this, I was curious if the Ford diesel truck had similar issues with their switch. Yes, they do.
In researching, I found that the Ford switch looks exactly the same, except for the mounting bracket. Further research indicated the ford switch sends the computer a signal at aprox. 10"wc or less. Pretty close to the Dodge 8.5"wc. I figured just for the fun of it, I would check the salvage yard for a ford switch. I picked up two. Brought 'em back and they plug right in to the Dodge with exactly the same connector.

So, plugged it in, but no difference. Still have ABS and brake dash indicators on.

So here is my next question; Do I need to power down the computer to reset it?

I don't know what my next step is. The service manual doesn't show a procedure to test the low vac sensor(at least not that I could find)

I'm at a loss for next step in troubleshooting.
I will do Neal's suggested check of the servo, but I think I need to solve the brake/abs indicator lights on dash first.

???????
Thanks!

 

[Solar1]

A friend used a scan tool (i do not have one) and there were no codes showing. I just recently replace and set the TPS sensor and that was the only code showing. We cleared it after repair.