98 - 02 Cruise control woes

[MadMaximus]

My truck is a 2001 Dodge Ram 2500 with the 24v Cummins. Last summer I began to experience intermittent problems with my cruise control. This truck is very clean, never been driven up north in the salt. Everything but the cruise control works flawlessly.

When the problem began, it was random:

I would turn the cruise control on.
Set the speed
It would hold the speed perfectly for 5 to N minutes
Sometimes I would have no issues the whole trip.
Other times it would suddenly cut out, turn itself off and throw a P1595 Trouble code. (Cruise control solenoid circuit. Only way to get cruise control back on, was to turn the truck off and restart the engine.

This is not a vacuum issue but an electrical one, (although I did double check all the vacuum lines, etc)

Since I first started to try to track this down, the problem has grown to the point where the cruise control does not work at all.

At this time, if I attempt to even turn on the cruise control, the cruise light flickers and goes out or does not come on at all.

Here is what I have tried up to this point:

1. Checked and cleaned my grounds.
2. inspected wiring harness
3. replaced brake pedal switch.
4. Replaced the clock spring
5. Purchased a snapon solus pro and then performed the following diagnostic procedure you can find at moparman1973.com: https://mopar1973man.com/cummins/ar...4/p1595-speed-control-solenoid-circuits-r128/
6. From that procedure, I validated that wiring from the servo to the PCM was good, wiring to brake pedal switch was good.
7. 5 I even removed the cruise control switches, disassembled, cleaned and tested them.
8. 6 I have a spare PCM and a spare speed control servo, tried swapping the server and then the PCM, to no avail.

The only thing I can think of is that I either have 2 bad PCMs or 2 bad Speed control servos or both.

Is there anything else I need to check or something that I have missed? I am at a loss.

 

[petersonj]

This is probably not your problem, but it is definitely worth a check. On my '02 with a manual 6 speed transmission, the cruise control is controlled by the ECM (not vacuum operated), but the routing of the wiring going up to the switches in the steering is probably similar. Over the last almost 400,000 miles I have had three separate instances where a wire broke inside the insulation by the steering wheel tilt mechanism. It was caused by the operation of the tilt feature - not a very good design.

Fortunately, there is easy access to inspect the wiring where it flexes when the tilt mechanism is operated. Just remove the lower plastic piece just below the tilt handle. Inspect the wiring carefully. Don't be fooled if it looks fine. Twice on my truck the strands of wire were broken inside the insulation, but the insulation itself was still intact.

- John

 

[MadMaximus]

This is probably not your problem, but it is definitely worth a check. On my '02 with a manual 6 speed transmission, the cruise control is controlled by the ECM (not vacuum operated), but the routing of the wiring going up to the switches in the steering is probably similar. Over the last almost 400,000 miles I have had three separate instances where a wire broke inside the insulation by the steering wheel tilt mechanism. It was caused by the operation of the tilt feature - not a very good design.

Fortunately, there is easy access to inspect the wiring where it flexes when the tilt mechanism is operated. Just remove the lower plastic piece just below the tilt handle. Inspect the wiring carefully. Don't be fooled if it looks fine. Twice on my truck the strands of wire were broken inside the insulation, but the insulation itself was still intact.

- John

Thanks John, I will add that to my list of things to check. Its definitely possible. I should mention my truck is an Automatic Transmission, but I don't think that makes a difference for this issue. Thanks.

 

[petersonj]

I should mention my truck is an Automatic Transmission

You did mention it, indirectly - you said you have a vacuum controlled cruise control. My '02 6 spd manual transmission is controlled by the ECM - no vacuum servo valve and cable. I believe all manual transmissions of this era have ECM controlled cruise control.

- John

 

[MadMaximus]

You did mention it, indirectly - you said you have a vacuum controlled cruise control. My '02 6 spd manual transmission is controlled by the ECM - no vacuum servo valve and cable. I believe all manual transmissions of this era have ECM controlled cruise control.

- John[/QUOTE
ON my truck the throttle is controlled by a cable which is operated by a vaccuum servo, which is operated by 3 electronic solinoids which in turn are controlled by the PCM which also talks to the ECM.

So my Cruise system (factory) includes the speed control servo, PCM, brake pedal switch, cruise control buttons on steering column, clock spring and various wires connecting all these components. Hope that helps.

Also, when you said your steering column wires were broke, how were you able to tell that they were broken internally? Also, did you have any other issues, like starting issues or airbag issues, since I think all those wires run down the steering column.

 

[petersonj]

@MadMaximus wrote:

"Also, when you said your steering column wires were broke, how were you able to tell that they were broken internally? Also, did you have any other issues, like starting issues or airbag issues, since I think all those wires run down the steering column."

I was able to tell which wire was broken internally because the insulation would bend and stretch easily at the internally broken location.

And yes, all the wires do run down the steering column, but not all of them pass through the same location where the flexing occurs. I THINK that the group of wires that I am referencing supply the clockspring. The third time a failure occurred, a ground wire also broke at a nearby connector causing an anti-lock brake lamp, no speedometer, no HVAC, and an airbag lamp.

- John

 

[MadMaximus]

Ok, that makes sense. I had to go take my son to work today, so on a whim, I put the tilt all the way up and then hit the cruise button, it actually lit and stayed on for a few seconds before going out, so I think this lends credence that the issue is the wires at the tilt junction. Next step is to pull that a part and see what is going on there. I will keep you posted.

 

[MadMaximus]

Are these the wires for the cruise control buttons? (See photo)

 

[petersonj]

I think the two wires on the right may be the ones that I repaired. If they are red/light green tracer and black/purple tracer, then they match the wiring diagram below.

- John

 

[LorenStrodtman]

I think the two wires on the right may be the ones that I repaired. If they are red/light green tracer and black/purple tracer, then they match the wiring diagram below.

- John
View attachment 142738

Eight years and 91k miles of no Right switch control, NOS replacement switch installed, etc., just to find out it could likely be a damaged V37 ground wire ! The left switch works fine.

 

[MadMaximus]

Ok, I isolated the cruise wiring, its the red/light green wire and black /light blue wire. I cut out the part that bends with the tilt wheel and soldered in replacement wire. Still does not work. Now I am also getting a P1596 in addition to my P1595 trouble code.

Testing voltage with clock spring connector unplugged, the PCM is supplying 5.196 volts to cruise control switches. I believe its determining which button is pushed by how the voltage drops when you press a button, as it makes the current go through a different resistor according the the diagram.

The P1596 code is speed control switch too high, which I am taking to mean the current is not being drown down enough. I tested the resistances of the switches and they seem consistent but the manual does not say what the resistance really is, so I cannot say if these are good, or not.

I have stitched together all my manuals electrical diagrams of the cruise control system into one diagram to make it easier to follow. The green highlights are the wires I know are good and have tested.

Based on this diagram and the code I am getting, the issue has to be between the cruise control buttons and the PCM. There must be a wiring fault there somewhere or the switchs.

I thought about just running new wires from the clock spring to the PCM (wires V37 and K4) but I think the fact that the PCM is supplying a steady 5 volts, would make me think the wiring is not the issue.

Any thoughts are insights are greatly appreciated. I wish I could talk to the engineer who designed this.

 

[petersonj]

Eight years and 91k miles of no Right switch control,

Nine years and 197,000 of no left cruise switch operation miles for me. It was someone here on the TDR that pointed me to the wiring issue - can't remember the source - so I just keep passing the information on.

 

[petersonj]

Now I am also getting a P1596 in addition to my P1595 trouble code.

The P1596 code is speed control switch too high, which I am taking to mean the current is not being drown down enough.

At any time during the repair, was the ignition switch turned to the "run" position? Have you tried clearing codes to see which ones come back?

Nice job with stitching the wiring diagram together.

Since the original DTC set was the 1595 (Speed Control Solenoid Circuits), could there be a fault with one of the solenoids?

Other times it would suddenly cut out, turn itself off and throw a P1595 Trouble code.

When you say, "turn itself off", do you mean the cruise control stopped working and the cruise control lamp stayed lit, or do you mean the cruise control stopped working and the cruise control lamp went out?

This is not a vacuum issue but an electrical one, (although I did double check all the vacuum lines, etc)

Did you use a vacuum pump / gauge to test the vacuum circuits for leaks?

- John

 

[MadMaximus]

At any time during the repair, was the ignition switch turned to the "run" position? Have you tried clearing codes to see which ones come back?

Nice job with stitching the wiring diagram together.

Since the original DTC set was the 1595 (Speed Control Solenoid Circuits), could there be a fault with one of the solenoids?



When you say, "turn itself off", do you mean the cruise control stopped working and the cruise control lamp stayed lit, or do you mean the cruise control stopped working and the cruise control lamp went out?



Did you use a vacuum pump / gauge to test the vacuum circuits for leaks?

- John

I have cleared the codes multiple times, they come back. The P1595 refers generically to some sort of problem with the solenoid circuit, however the P1596 specifically references the voltage coming from the buttons on the steering wheel ae too high.

I actually used a Scan Tool (Snap-On Solus Pro) to activate the solenoids, and I can hear them clicking (ignition on, engine off), so I am pretty sure that's working. I also have tried 2 different ones.

"turn itself off" means that the cruise light goes out. The issue is an electrical issue. I cannot even get the cruise control to stay on long enough to set a speed.
Basically, I cannot even turn the cruise control on at this point.

I have not tested the vacuum recently, but I can report I inspected all visible lines and they look good. Additionally the HVAC plenum controls work, which are vacuum operated. Lastly, if vacuum was the issue, the system would function electrically and throw no codes, it just would not hold a speed. I wish is was a vacuum issue,.... would be much easier to fix and identify.

 

[petersonj]

I agree, I think you have an electrical issue. The information below is from my 2002 FSM. The P1595 code's description is a little more definitive.

P1595 - Speed Control Solenoid Circuits - An open or shorted condition detected in the speed control vacuum or vent solenoid circuits.

P1596 - Speed Control Switch Always High - Speed control switch input above maximum acceptable voltage.

I am thinking that you may have two separate issues. I think the P1596 code was introduced during your wiring repair. You have checked for power from the PCM via the RD/LG wire at the disconnected clock spring. Have you checked the ground circuit from the disconnected clock spring (BK/LB wire) to the sensor ground terminal on the PCM? An open in this circuit would coincide with the Code P1596.

As far as the P1595 code, that could be an open or a short in the vacuum or vent solenoid circuits - a short could be a short to ground or a short to another wire.

For intermittent wiring problems I would perform the wiggle test with an ohmmeter hooked up to the circuit in question. Any deflection of the reading while moving the wiring harness around would indicate a poor connection at some point.

It seems that you are very capable diagnosing electrical problems, so you may have already done this.

- John

 

[MadMaximus]

I did measure the voltage at the clock spring connector, it read 5.196 volts
The P1596 might have been triggered by testing the voltage with the ignition on, engine off, as it would have sent the current through tester, not the resistors in the switch.

SO this is what I am thinking... the PCM is supplying about 5 volts to the switches. Its supposed to drop by a certain amount to determine on / off, set, coast, etc. I just don't know what exact voltages its looking for.

As for shorts, broken circuits etc, I did a long diagnostic procedure i found on mopar1973man .com, all the wires checked out, but all some of that test procedure ended up coming to conflicting conclusions and none of it tested siring between the cruise control buttons and the PCM.

Not sure where to go from here.

 

[LorenStrodtman]

the manual does not say what the resistance really is, so I cannot say if these are good, or not

I feel your pain on this topic.

I did a long diagnostic procedure i found on mopar1973man .com

I will laugh if that procedure was written by Tractorman.

 

[MadMaximus]

Tested speed control servo again last night.
Procedure:
Connected SnapOn Solus Pro to ODBII port.
Turned ignition on, engine off
Selected functional tests (after setting by my vehicle with auto identification.
Performed the following 3 tests:

• Commanded Vacuum solenoid on: passed (can hear solenoid click)
• Commanded vent solenoid on: Passed (can hear solenoid click)
• commanded speed control solenoid on: Passed (can hear solenoid click)

With this tests the SnapOn scan tool is commanding the PCM to turn the solenoids on, which confirms that both the solenoids are working and also the wiring between them and the PCM and that the PCM is able to send signals to the solenoids.

So where does that leave me? I have no idea.

Is it possible the PCM can be commanded to turn them on but still be malfunctioning when trying to use the cruise control? Although, I have tried two diff PCMs.

I really don't know where to go from here other than install an aftermarket Cruise control. Which I can do... but really wanted to be able to use the factory CC.

Any last thoughts or words of wisdom?

Anybody know a Dodge engineer from 25 years ago?

 

[petersonj]

I have run out of ideas. Since I am not familiar with the servo valve setup, does the servo valve include the vacuum actuator that pulls on the throttle, or is the vacuum actuator separate?

- John

 

[Ozymandias]

You have changed everything but the cheap switches in your steering wheel.