Hi all. I recently rebuilt the hydroboost on my Yukon, and afterwards the cruise control and brake lights didn't work. I put a new brake switch on, but that didn't help. Discovered a blown fuse for the brake lights, so now they work, but I still have no cruise control. I had been getting an occasional service stability message before the hydroboost rebuild, but since I put on the new brake switch and replaced the blown fuse I get the message every time I crank the vehicle. No noticeable change in performance though. I thought I'd check the OBD2 for codes, but my reader says linking error when I try to read them. The reader is getting power and I've confirmed that it works on a different vehicle. I also noticed that when it tries to start communicating with the car, there is an audible pop from the speakers (a clue perhaps?). Lastly, I checked every fuse in the panel on the drivers side of the dash and in the fuse box under the hood next to the battery for continuity. They all checked out good. I don't know if these problems are related or independent, but they certainly are annoying. Any ideas?
06 Yukon Denali service stability message, no cruise control, OBD2 port has power but no communication
- Thread starter bama_dave
- Start date
Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
MassHoe04
Full Access Member
Since cruise gets turned off when brakes are applied and you are having weird electrical things... Maybe something related to the brake light switch or the wiring to/from?
Maybe the switch is bad and the cruise thinks the brakes (brake lights) are still on. Since the fuse for your lights did blow that last time, that is what is making me think that maybe something with the switch is funky.
Maybe the switch is bad and the cruise thinks the brakes (brake lights) are still on. Since the fuse for your lights did blow that last time, that is what is making me think that maybe something with the switch is funky.
Any idea how I can verify that? Voltage on a wire, fuse, etc? It’s a brand new switch, and the brake lights are functioning properly, but I do think I remember reading somewhere that the switch could still be faulty in spite of those things.
rockola1971
Full Access Member
Hmmm What does cruise control and brake light control have in common...... TAC Module and Serial Data to the pcm. The fact that you cant successfully connect to PCM with a scanner leads me first to have a look at serial data line for a short to ground which would bring the voltage down at that comm wire enough to cause the PCM to see gibberish. Dont confuse power wires with serial data wires. Power wires are either 12v or Ground. Serial Data wires are use for communication from various devices in the vehicle to the master module that communicates with that specific device. In this case the PCM to the TAC module and the TAC module is up by your Hydroboost on the firewall. Did you pinch a wire when working on the hydroboost? Open files with irfanview. 
Attachments
Last edited:
Everything seemed ok around the TAC Module. Nothing obviously pinched/frayed/corroded. I'm trying to look at the schematics you attached and figure out how to start eliminating possible sources of the problem. Am I correct that the cruise fuse should have 12V with the key in the run position? And the GY/WH wire coming from the multifunction switch should have 12V with the key in the run position and the cruise switch set to on? Then the D-BU goes hot if I press and hold the set button while probing? If I'm correct and those are true, wouldn't that rule out everything up to and including the multifunction switch as the problem? I'm hoping to have some time tonight to start checking things off the list.Hmmm What does cruise control and brake light control have in common...... TAC Module and Serial Data to the pcm. The fact that you cant successfully connect to PCM with a scanner leads me first to have a look at serial data line for a short to ground which would bring the voltage down at that comm wire enough to cause the PCM to see gibberish. Dont confuse power wires with serial data wires. Power wires are either 12v or Ground. Serial Data wires are use for communication from various devices in the vehicle to the master module that communicates with that specific device. In this case the PCM to the TAC module and the TAC module is up by your Hydroboost on the firewall. Did you pinch a wire when working on the hydroboost? Open files with irfanview.
Attachments
rockola1971
Full Access Member
Am I correct that the cruise fuse should have 12V with the key in the run position?
Yes
And the GY/WH wire coming from the multifunction switch should have 12V with the key in the run position and the cruise switch set to on?
Yes
Then the D-BU goes hot if I press and hold the set button while probing?
Yes
BUT.... I dont think you can successfully enable cruise control mode in park, zero speed in your driveway. Give it a try and see if you can get cruise to show on in the Instrument Cluster. Not sure how to tell if enabled without a tech 2 or the like.
Id be more worried about why your PCM wont communicate with your scanner. Something is bringing down your serial data line. May be related to your initial blown fuse. Which one was it that blew?
Yes
And the GY/WH wire coming from the multifunction switch should have 12V with the key in the run position and the cruise switch set to on?
Yes
Then the D-BU goes hot if I press and hold the set button while probing?
Yes
BUT.... I dont think you can successfully enable cruise control mode in park, zero speed in your driveway. Give it a try and see if you can get cruise to show on in the Instrument Cluster. Not sure how to tell if enabled without a tech 2 or the like.
Id be more worried about why your PCM wont communicate with your scanner. Something is bringing down your serial data line. May be related to your initial blown fuse. Which one was it that blew?
It was the brake fuse in the under-hood fuse box. And I'm thinking that I tried to read codes some time ago and had this same issue before the cruise went out, so it's possible that the two are unrelated. Regardless, it's a problem I'd like to fix if I can.
BUT.... I dont think you can successfully enable cruise control mode in park, zero speed in your driveway. Give it a try and see if you can get cruise to show on in the Instrument Cluster. Not sure how to tell if enabled without a tech 2 or the like.
-I know it won't show up on the cluster, but will some or all of those wires we were discussing have power even if it doesn't show up? May test it out in the morning either way. Time got away from me tonight. My wife called me earlier from about 30 minutes away and couldn't get the yukon in park so I had to go save her. The shift interlock solenoid was disconnected from the forward ball joint. It still works, but it's cracked or something and doesn't want to stay on very well. It put me behind schedule on getting other things done, but on the bright side, I took all the trim off around the column so now I can easily access the multifunction switch and all the other junctions for testing in reference to the cruise control.
rockola1971
Full Access Member
I would make it a quick and dirty check at the TAC module terminal 14, 4 and 5 while somone is actuating the switches for you. They are all 12v. If they are all there at the TAC module then you dont have to be laying on your back in the floorboard poking around in the steering column looking for wires. If one is missing then work backwards in the schematic for the terminal that has 0v on it when it should have 12v on it when the correct switch is actuated.
I didn't have a helper handy, but I was able to easily probe at the pigtail for the multifunction switch on the column since I had all the trim taken off (posted a couple pictures of it just for reference). Multifunction switch is working as expected. I got a new shift interlock solenoid and installed it. Amazing how such a small piece of plastic braking off can ruin your day (see the picture of it as well). After installing it in the parts store parking lot, I tried my cruise on the way home. It worked. Then on my next drive I tried it again and it no longer worked. It's got me back to wondering if it might be something to do with the brake switch. Do you have any info on it? I checked every wire at the brake switch with the multimeter and they were all hot except for the white one, and it goes hot when you press the brake pedal (as it should per the schematic you shared before). Should all the other wires be hot all the time though? Seemed odd for so many to be.
rockola1971
Full Access Member
In the schematic I see A Orange wire feeding 12v (Hot all times) to brake switch. When brakes are applied the brake switch close (Normally Open switch) and the White wire then gets the 12v and that feeds to the Vehicle Stop 15a fuse then ultimately the TAC module terminal 6 via the Light Blue. This is how the cruise gets shut down when you press the brakes.
Im curious if you have 12v on TAC module terminal 6(LT BLU Wire) ONLY when the brakes are pressed?
Im curious if you have 12v on TAC module terminal 6(LT BLU Wire) ONLY when the brakes are pressed?
