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Avalanche Owners Zone => Chevrolet Avalanche Problems, Questions & Answers => Problems: Drivetrain & Steering => Topic started by: tommckay on June 30, 2018, 09:31:06 AM

Title: Help with drivetrain issue
Post by: tommckay on June 30, 2018, 09:31:06 AM
I tried searching for this issue and couldn't find anything exactly matching my problem. At least I dont think so....

My issue happened to me this morning. I was running on the freeway and I got a service 4wd on the DIC and the speedometer started dropping even though I wasn't slowing down. Then as it dropped it stopped driving the wheels, like it was in neutral.  Once slowed down to about 20mph, it will kick back in and I can reestablish speed... until it happens again.

I also have a problem with the speedometer being inaccurate.  It will say 58-59mph when I'm doing 77mph according to my GPS.

I'm also having problems with the speed control randomly accelerating beyond my set point. Set it at 75mph, and it will run up above 80 and want to keep going.

Any thoughts on this would be appreciated.
Title: Re: Help with drivetrain issue
Post by: MS03 2500 on June 30, 2018, 09:59:15 AM
I would go to auto parts store and have the codes read.
Title: Re: Help with drivetrain issue
Post by: tommckay on July 1, 2018, 05:22:45 AM
Another question for those smarter than I.

I bought a Range device to do the DOD disable, but as soon as I plugged it in and started the truck, it made my fuel gauge and oil pressure gauge fluctuate dramatically and I saw the service 4wd on the DIC. I immediately shut it off and unplugged the unit. When I restarted it all seemed normal again.
But then the above happened with she service 4wd issue.
Title: Re: Help with drivetrain issue
Post by: redheadedrod on July 1, 2018, 07:37:19 AM
It is always best if you can post what year your truck is...

Also did the issues happen before you used the range device?

If not the first thing I would do is disconnect the battery for an hour or so and reconnect. Then do NOT reuse that Range device as you likely have a defective device. Very common with "clone" devices with other types of devices so I wouldn't be surprised if it is the case here too.

Title: Re: Help with drivetrain issue
Post by: tommckay on July 1, 2018, 18:24:29 PM
Yep...   I have a 2007 LT with 80,400 on the odometer.  That could help. sorry.

I bought the Range device directly from the Range technology website, so I would think it wouldn't be a clone.

the issue never happened before I tried the range device, but I took off on a trip and it started at a point further than I had ever driven it at one time before so I really don't know.

I will be writing Range Technologies to tell them what happened and see what their response is.
Title: Re: Help with drivetrain issue
Post by: redheadedrod on July 2, 2018, 05:59:19 AM
I would certainly pull the negative battery terminal and let it sit for at least an hour and reconnect to see if your issues fix themselves.

And definitely contact the manufacturer. Expect they will try to deny they caused your issues and don't offer up possible excuses.

Your truck didn't do that before you added their device and now it does.

Do you have to leave it plugged in for it to work or do you program something with it and unplug it when its done?

Title: Re: Help with drivetrain issue
Post by: Vaeagleav on July 2, 2018, 07:11:18 AM
From reading older threads about the Range AFM device the way I remember it, they install the device under the dash and leave it plugged in to stop AFM. There was one or two people who found out over time that there was a parasitic drain of power if left parked and caused issues. I believe they removed the Range and drain went away.
Title: Re: Help with drivetrain issue
Post by: tommckay on July 2, 2018, 18:55:14 PM
It has instructions on the Range AFM disabler stating to unplug it if your going to leave your vehicle sit for more than a few days due to battery drain. You just plug it in to the OBD2 port and leave it there
 When you take it out your truck returns to AFM (DOD)
 

I contacted Range Technologies and their customer service was good. They are sending me a new one they will test and certify. And pay the return postage on the old one.

When I return home from vacation, I will do the battery disconnect and look for any blown fuses.
Title: Re: Help with drivetrain issue
Post by: tommckay on July 28, 2018, 13:01:38 PM
Follow up. Thew new Range Technology device seems to work perfectly.

My other issue still exists. But I've had it scanned and while there were 10 codes, none of them made sense to the shop. So he cleared all codes and I went for a drive to reproduce the error. I was successful in reproducing the error and returned to the shop to re-read the codes. There was only 1 code. But it only pointed to the speed sensors. Replaced them.

Speedometer is still off 10-16mph at freeway speeds.

I've also noticed the issue is speed related!  If I keep the speeds 75mph or less. It will no happen. I just took a 275mi trip kept it at 75 and under for the 1st 220 miles and it was great (except the cruise wanting to accelerate beyond set point). That's when I had the reoccurance. The cruise crept up to 80 and I instantly got the s"service 4wd" message, speedometer dropped to 0 and truck went to neutral. Slowed down into the shoulder, kicked back in at 40mph and I reaccelerated to 75mph. Did not reset the cruise and manually kept the speed at 75 for the next 55 miles and it never happened again.

I'm going to take it back to the shop with my latest discoveries and see what they can come up with.

Anyone have possible insights?
Title: Re: Help with drivetrain issue
Post by: tommckay on September 9, 2018, 08:09:54 AM
More history to this ongoing saga....

I had both speed sensors replaced and it did not correct my speedometer issue.

This is definitely an issue that is speed related.  But after another 350mi round trip I paid attention and noticed some more points to ponder...  I'm using my GPS as a speedometer and my foot as my "cruise control". The last trip I kept it to about 72mph on the GPS, speedometer would vary... when I first hit the highway I would run it up to 7smph on the GPS and the Speedo would read 65. but as I continued keeping the speed at 72 (+or- 2mph) the speedo would slowly reduce shown speed down to 55mph, periodically dipping down to 50mph (while I maintained 72mph). 

I found that if i kept it at 72 and the speedometer dipped below 50mph it would set the service 4wd on the DIC and reduce power and set it in to "neutral" until I slowed it down below 40 and it will kick back in for me to resume speed.  On the return trip, I experienced the same issue but by watching the speedometer and seeing when the needle dropped to 49mph, i could lift off the throttle and feather the gas until the needle picked back up above 50. That meant slowing to about 68mph.

On this last trip I did about 55 miles on 2 lane road with a 55mph speed limit. at 60mph the speedometer seems to hold pretty steady at 52mph. so I tried the cruise and it worked exactly as it should with speeds variying between 58 and 62 on the GPS as I went up and down hills.

With these observations in mind I took it to the local Auto electrical repair shop and they inspected everything. Verified the Body Control Module was working properly, did a reprogram of the Brake Control Module and the speedometer is still off. They took it out for a drive with their diagnostic equipment attached and said the PCM is outputting exactly what the Speedometer is reading. So with everything they've checked and verified is good, they recommended replacing the PCM. Everything is pointing to that. Get this, since what they did didn't fix the problem, they did not charge me anything for the diagnostics they did.

So now I found a new PCM from Flagship One Inc. that they will send me preprogrammed to the VIN of my truck That I'm going to have put in. I'm really hoping this will resolve the issues. So we'll see.

Any thoughts?
Title: Re: Help with drivetrain issue
Post by: tommckay on October 7, 2018, 19:00:30 PM
Latest update to the ongoing saga......

I replaced the PCM and it is still not right. A little better, but not right.

I was able to take my first extended trip since the PCM replacement and the Speedometer will read up to 18mph slower than actual speed, but it doesn't vary much anymore and I am able to use the cruise a bit as long as I keep my eye on actual speed. It will try to take off and accelerate after cresting hills and heading down the other side.

HOWEVER....  A couple of new issues cropped up.   
#1 - When the cruise is on at 70mph (GPS) -or- 58mph (Speedometer) it will accelerate 2-3mph when going around a curve to the right and slow down by 2-3mph when going around a curve to the left.

#2 - The tow/haul feature will activate on it's own. The dash light will start flickering as I'm driving and then then the truck went in to limp mode with no errors showing and the tow/haul indicator light came on solid, the limp mode ended when I coasted down to 60mph while feathering the gas and then picked up but was obviously in tow mode. I played with the on/off button on the gear shift for a little bit and got it to disengage. But it weird for sure.

So with this further information I will get back with the local repair shop and see what we might be able to do next.

Anyone here have any thoughts?
Title: Re: Help with drivetrain issue
Post by: redheadedrod on October 7, 2018, 20:53:01 PM
Sounds like you may have a bad ground somewhere...

Thats where I would start at this point.

Also if you are not running standard sized tires then your PCM needs to be adjusted. For my '03 that programming can be done with a tech 2 without reprogramming the whole PCM. Could be your issue since it can throw off everything else if your tires are a non standard size.
Title: Re: Help with drivetrain issue
Post by: ygmn on October 9, 2018, 05:52:30 AM
Bad stepper motor for Speedo?
Maybe tow/haul switch wires are chafed an shorting? (the wires tend to break)

Title: Re: Help with drivetrain issue
Post by: tommckay on October 10, 2018, 18:45:08 PM
Well, the truck has 20" rims, sporting 275/55R20, standard is 265/70R17. The Tire size comparisons are below - Very negligable and not antwhere near what I'm getting.

Tire Size Comparison Visualizer Show Alternate Sizes
Tire 1 Front View 10.8" 31.9"
Tire 2 Front View 10.4" 31.6"   

Tire 1 632 Revs/Mile 
Tire 2 638 Revs/Mile

Speedometer Error
(Set Size1 to OEM Size)

Reading  20mph 30mph 40mph 50mph 60mph 70mph 80mph 90mph
Actual     19.8     29.7    39.6     49.5     59.4    69.3    79.2     89.2


Besides, the speedo gets further off with distance/time. if I tke off and get right on the freeway, it will only be 5mph off for the 1st few miles and then the gap widens as I continue. at a constant 70 on the GPS the speedometer will eventually drop to a shown 58.


I have not checked grounds yet. but I will be before long. From reading there are grounds to the frame under the drivers seat area and under the hood to the fire wall.