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Discussion Starter · #1 · (Edited)
A guide to diagnosing cruise control problems on 96-97 Trucks

(This is a work in progress, I will add photos later if needed)

I am writing this up after chasing my tail for almost 2 weeks, fixing almost everything related to the speed control system. The previous owner said it had not worked in 10 years... He thought it was a fuse.

If you have a different year of truck, this *Might* help, but I dont know. I know the wiring in 1996-1997 rams is the same when related to cruise. I would recommend also thumbing through the service manual, I found one here: Manuals.

First, in order to get ANY power to ANYTHING in your cruise system you have to have the truck running, rev it to about 2k RPM, then the PCM powers circuit V32 (Yellow with red stripe) which provides power the the switches, while also sending through the brake switch to the servo.

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Step 1, Clock Spring: Does your cruise control light come on? If yes, you can most likely skip this step! The Clock Spring is a ribbon cable that allows things to stay connected when you rotate the steering wheel from left to right.

If not, does your horn work? (If not, it could also be as simple as a fuse) Does your Airbag light remain illuminated? If so, odds are its your clockspring. However, your clock spring can be bad and your horn still work, which happened to me. Cheapest I found a brand new one was $120, but I got mine from a pull a part lot out of a Ram 250 Van. The ones for 98-01 Rams are brand new $50, but require some splicing of the harness.

Testing: Use a Torqx driver (Mine was T20) remove the three screws holding the lower collum cover in place, exposing a flat plug. Unplug it. The farthest most drivers side wire will be yellow with a red stripe. This is the wire that powers the switches.

Now, remove the cruise buttons using a Phillips screw driver. Unplug them, see your little yellow wire with a red stripe? This wire is your friend. Now get out your trusty multi-meter. Your testing for a connection, not voltage, so use an ohms setting. Test connectivity between where the buttons plug in and the pins behind the steering wheel. Do you have a connection?

If yes, test the rest of of the wires that come from the cruise buttons.

If no, then your clock spring is bad. Congrats, you have found your problem!

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Step 2, Brake switch. Only move onto this if your cruise light is working. Do your brake lights work? This does NOT mean your switch is good.

V32 (The yellow wire with a red stripe) connect to V30 (Dark Brown with Red) through the Brake Switch. With the brake peddle not pushed, electricity should be able to pass through. Check this with your trusty multi meter. Also, try lifting the peddle. This part can be re-adjusted, which might help. A brand new one is $10 and installs with no tools in about 5 mins. Just replace it and save a headache.

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Step 3, Vacuum. Do your heater controls not work? This most likely your issue! A lack of issue with heater controls DOES NOT mean your vacuum is fine.

This is the most frequent problem that these cruise systems have. The vacuum line goes under the drivers side battery to the servo, where it gets corroded and begins to fail. Check your system for good vacuum.

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Wow, your clockspring is good, your brake light switch has been tested, and your vacuum is tight and awesome. Your cruise light comes on, but your set and acceleration buttons do absolutely nothing, or you start to set it and then it slowly looses speed. Move on to Step 4.

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Step 4, Cruise Servo: The last potential problem is the Servo. This is a bit more complex, because the part numbers are different now. According to the Dodge Dealer the old part number was 53009315, which they no longer have. They have replaced it with part number 4669979 which they want $150 for. They also told me that I will need a different wire harness, part number 3013979AB, which they want $50 for.

Remove the servo, there are two nuts holding it to bracket, a tiny little pin holding the throttle cable to the servo, a vacuum line, and an electrical plug. Some say you have to pull the battery tray, I was able to remove the servo just after pulling the battery, leaving the tray in place. Pull it out, visually inspect it. Mine had a big hole in it.

I can also tell you that the one in my 1993 ZJ Grand Cherokee is the exact same servo as the one in the Ram.

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Step 5, Fix a Surge Issue: Your truck has cruise control, but its funky and does not work right. Surges badly, ect. First, check the vacuum. If its good, then we have a fix for surging too!

(Chrysler put out this informational bulletin, not me)

If the vehicle operator **repeatedly** presses and releases the SET button with their foot off of the accelerator (a "lift foot set" to begin speed control operation), the vehicle may accelerate and exceed the desired set speed by up to 5 MPH (8 km/h) and then decelerate to less than the desired set speed before finally achieving the desired set speed.

The speed control has an adaptive strategy (ability to learn) that compensates for vehicle-to-vehicle variations in speed control cable lengths. When the speed control is set with the vehicle operators foot off of the accelerator pedal, the speed control "thinks" there is excessive speed control cable slack and adapts (learns). If "lift foot sets" are continually used, the speed control overshoot/undershoot condition will develop.

To "unlearn" the overshoot/undershoot condition, the vehicle operator has to press and release the SET button while maintaining the desired set speed with the accelerator pedal (not decelerating or accelerating), and then turn the speed control switch to the OFF position **(or press the CANCEL button, if equipped) after the speed control has been engaged for 10 seconds or longer.** This procedure must be performed approximately 10-15 times to completely unlearn the overshoot/undershoot condition.

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These trucks are almost 20 years old, if your cruise worked recently, you most likely have only one problem. If your truck is like mine, and has not had functional cruise for a decade, you should bet on more than one problem.

If your experiencing the cruise trying to "Run away" and just keep reving, a slow drop in speed, or you bought a junkyard servo this video may be helpful to you.
 

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Ten pages of tree type diagnostic charts for the cruise in this book.
Find it on ebay for cheap, it was only $10 new from Chrysler.

 

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what if when you set cruise and it just keeps getting slower and slower some times it will set and some time you can click the it and it wont do anything ???
 

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Discussion Starter · #4 ·
what if when you set cruise and it just keeps getting slower and slower some times it will set and some time you can click the it and it wont do anything ???
Although I do not have any personal experiance with this problem, it sounds like a lack of vacuum to the servo. I think step one would be investing in a vacuum testing gauge.

The other possibility is the servo failing. It is designed to control how much vacuum it vents and how much it maintains, if it is not able to properly limit the venting of the vacuum, then your cruise will not be able to maintain.

On my truck, 12 hours after parking and shutting off the engine, the vacuum system is still tight and I will hear a hiss when I seperate any of the hoses.

What steps have you taken so far to diagnose the problem?
 

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Nice write-up The Joe. I would say start with the servo first though. These are notorious for getting eaten up by the acid from the driver side battery. Nothing like putting a critical part under a battery. The good old Mopar Engineers must have been hard at work figuring out ways to cost us money with dumb ideas like this!
 

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One other thing to add only because it took me forever to figure it out. If anyone has done the relay mod to lock out overdrive on start up instead of manually locking it out with the switch this could also be your problem after I removed the relay it works as it should.
 

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Thanks Joe - step 5 is exactly what is happening to my 98 12v. Does anyone know if that "fix" applies to the 98 cruise as well?
 

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Discussion Starter · #8 ·
Added a video to the post that will help with people who want to refurbish a servo that is still intact but has some personality flaws, things like when the cruise trys to continue accelerating, or slowly decelerate. Check it out!

Thanks Joe - step 5 is exactly what is happening to my 98 12v. Does anyone know if that "fix" applies to the 98 cruise as well?
I dont know if it does or doesnt, I have not spent enough time under the hood of any 98s. It *Should* since the fix is for the servo itself and works on many different cars and trucks that have had this save style servo.
 

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My cruise control works perfectly, EXCEPT, when I'm going down a hill. Granted, a decently steep grade. Once I crest the hill, everything works fine, until about another 100 yards, then my truck jerks pretty hard. It'll do this every 100 or so yards until im at the bottom. It really feels like the truck is cutting out, but i know thats not the case, because if the cruise is off, it just moseys on down the hill no problems. Is this the surging issue you were talking about? Or do I have something totally different going on?
 

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Discussion Starter · #10 ·
My cruise control works perfectly, EXCEPT, when I'm going down a hill. Granted, a decently steep grade. Once I crest the hill, everything works fine, until about another 100 yards, then my truck jerks pretty hard. It'll do this every 100 or so yards until im at the bottom. It really feels like the truck is cutting out, but i know thats not the case, because if the cruise is off, it just moseys on down the hill no problems. Is this the surging issue you were talking about? Or do I have something totally different going on?

Thats an odd issue, I wish I had some helpful input, but that is new to me.

The surging I talked about seemed to be more when you set the Cruise control and it would try and accelerate more than you wanted. Best of luck figuring it out, and if you get an answer, please share it with us in this thread.
 

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what if when you set cruise and it just keeps getting slower and slower some times it will set and some time you can click the it and it wont do anything ???
I would look at the electrical wiring. A little corrosion in a connector can cause intermittent electrical issues. Sometimes things work, sometimes they do not. I had a starter that sometimes would work and other times it would do nothing. Removing the wires and cleaning up the ends ended up with a starter that always worked.
 

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Thats an odd issue, I wish I had some helpful input, but that is new to me.

The surging I talked about seemed to be more when you set the Cruise control and it would try and accelerate more than you wanted. Best of luck figuring it out, and if you get an answer, please share it with us in this thread.
It's done it ever since I've owned the truck, and I've had other 2 gen 12V folks have the same issue. I can live with it, i was just curious. Thank you.
 

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My cruise control works perfectly, EXCEPT, when I'm going down a hill. Granted, a decently steep grade. Once I crest the hill, everything works fine, until about another 100 yards, then my truck jerks pretty hard. It'll do this every 100 or so yards until im at the bottom. It really feels like the truck is cutting out, but i know thats not the case, because if the cruise is off, it just moseys on down the hill no problems. Is this the surging issue you were talking about? Or do I have something totally different going on?
Does it happen on steep enough hills where the truck accelerates downhill with no throttle? I imagine this is somehow related to the fact that diesels don't really engine brake... The service manual only has one somewhat related thing:

"Hunting surge or speed variations at low speeds" ->
"Torque converter/Clutch roughness" ->
"Amplification of engine surge" ->
"Defective Servo" ->
"Defective Cable" ->
"Defective powertrain control module".

Hope maybe that helps some.
 

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I have been having a problem with my cruise (1st gen, but I'm hoping someone else can come up with something I haven't) I can set the cruise, it will hold for a period of time, anywhere between 10 seconds and 100 miles. never know how long it will last. usually lesser time. I have tried replacing the brake light switch because the last trailer I pulled I could see the reflection of brake lights randomly flashing. didn't fix the cruise issue. I've checked the vacuum hose going to the cruise, good. I thought a bad relay, when a relay begins to go bad, it can over-heat and quit. I can not find a cruise control relay. I'm thinking a bad servo next? any suggestions please
 

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1998 TRUCK CRUISE ELECTRONICS DIAGNOSIS:

The wiring is slightly different on these trucks. Cruise switch signal coming out of the clockspring should be red with a light green tracer. The ground is black with a light blue tracer. IMO, this should be the electronics test sequence if you cannot get your cruise light to turn on:

1.) Disconnect negative battery terminals and wait 2 minutes. Remove airbag with (2) 8mm bolts to expose cruise switch wiring. Remove switches with torx bit. Test switch continuity. Resistance values are as follows, +/- a few % should be acceptable:

ON: 909 ohms
SET: 6650 ohms
RESUME/ACCEL: 15,400 ohms
CANCEL: 0 (closed circuit)
COAST: 2940 ohms

If your ON ohms are something crazy like 450, you need a new switch. If switch values are ok proceed.

2.) Clockspring continuity. My horn worked, and airbag light was off, but my clockspring was still bad. Know for sure by checking continuity with multimeter. Take the column cover off and you will see where a flat rectanguler connector goes into the clockspring. Remove and test far right pin with the connector that clips into the buttons. Make sure to test both sides of the button connector, one is a ground that goes back through the middle pin in the rectangular connector. Check that as well. My clockspring had no continuity in the speed switch signal wire, had to replace.

3.) If clockspring and switches are good, check underneath the column for broken wires. On 98 it should be the red with green tracer and black with blue tracer. If wires are good, check connection at PCM. You also can replace the brake switch, however this does not turn the cruise light off, it just disengages the servo.

4.) If everything has checked out, continuity good everywhere and you've used dielectric grease on all the connectors, try looking into the neutral safety switch for manual trans and some sort of neutral switch for auto trans. It has been discussed that this is a possible component in the system that needs to be verified before the computer will turn cruise on. If the neutral switch is fine, you're probably looking at a bum PCM. Your life sucks.
 

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I am having a somewhat similar issue with my 98 12v. My problem is that my cruise maxs out a 55 mph and it just wont make any more. Doesnt seem to surge or anything just dead heads at 55. Any ideas or directions to go would help huge.

Thank you!!!
 

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^cable adjustment/problem?

Cruise drops out randomly or on bumps. ~ The brake switch is fine, but
> switch bracket needs bent/adjusted
> pedal is not returning enough or bushing worn.

If it's bad it will affect TC lockup to, but that seems less sensitive.
 

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I am having a somewhat similar issue with my 98 12v. My problem is that my cruise maxs out a 55 mph and it just wont make any more. Doesnt seem to surge or anything just dead heads at 55. Any ideas or directions to go would help huge.

Thank you!!!
On that, I'd suspect a minor vacuum leak (either in the lines somewhere, or the actuator itself). The actuator is located under the drivers side battery and they're known to rust out, and 17 year old rubber hoses can get dried and cracked... I.E., I suspect everything is 'working' correctly (electrics are good, the controls are good, the ECU is good, the brake switch is good, etc), but the actuator doesn't have enough vacuum power due to a leak, to pull the fuel lever hard enough to get past 55.

The vacuum system is (supposed to be) pretty well sealed. I can pop one of the hoses off 10 minutes after turning my truck off and there's still a vacuum in the lines (you can really noticeably hear a 'pop/suck' on disconnecting a line). If you crack a vacuum line and don't hear that noise, you've got a leak somewhere.

Jim
 
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