1998 Cruise Control troubleshooting

[TylerG]

I inherited my dad’s 1998 K1500 and have been working on restoring it. I rebuilt the 5.7L myself and had the 4L60E rebuilt. I’ve been frequently taking 10 hour road trips and I’m trying to get the cruise control working.

Troubleshooting to date:
- replaced the multifunction switch (wipers not working)
- tested the voltage at all the pin connectors at the cruise module, per the manual (and YouTube video). Everything checked out.
- opened the module and checked the condition of the gears. Everything looked good.
- bought a used module on eBay and tried it. No luck.

I’m about ready to resolder the board connections. However, the fact that the second module doesn’t work makes me think that’s not the problem.

Is there a way to check the signal coming to the cruise module from the ECM/transmission? I’ve read where someone put the rear up on stands and checked operation above the minimum speed. Don’t know if that’s a wise course of action and what form the signal would take.

Anything other suggestions?

 

[Awest623]

Take a look through this manual. When I repaired the cruise control on my 98 I went through 3 junkyard modules before I found a good one. The speed signal should be a square wave that increases in frequency as speed increases

 

[Orpedcrow]

I’ve read where someone put the rear up on stands and checked

That’s how I checked mine and determined a faulty cruise control module.

Chock the front wheels and make sure you use Jack stands under the axle. Gentle application of the brakes will help prevent a dangerous, sudden transfer of energy

 

[TylerG]

Take a look through this manual. When I repaired the cruise control on my 98 I went through 3 junkyard modules before I found a good one. The speed signal should be a square wave that increases in frequency as speed increases

Great!! Thanks! Just what I was looking for. I’ll let you know how it comes out

 

[Awest623]

Great!! Thanks! Just what I was looking for. I’ll let you know how it comes out

For future reference that manual is from a sticky in the engine section. There's a collection of factory service manuals there

 

[TylerG]

Problem solved! New ECM

I put the cruise control troubleshooting on the back burner because of higher priority projects. The CEL had been coming on intermittently for several months and often clearing itself a few hours later. The codes started off MAF Circuit Low, O2 Sensor and EGR and grew to include both banks lean and a bad throttle sensor, plus the transmission started shifting poorly. I checked signals from the O2 sensors, MAF and the fuel trims and everything was in a normal range. No vacuum leaks either. Decided to get a new ECM for only $120. It needed only minutes to install and 30 minutes to reprogram the security interlock. All the codes have disappeared and the truck runs like new.

Best of all, the cruise control works again. I'm sure the troubleshooting would have shown that it wasn't getting a signal from the ECM.

I'm amazed that a replacement ECM is so inexpensive, since I hear horror stories from everyone paying over $1000 for a replacement on their new cars.