Need 98 Tahoe help

[RENODMAX]

One of my younger brothers friend's tahoe took a crap on him yesterday. He was driving it when it decided to quit putting power to the ground. It will rev up normally and sometimes will creep forward, most of the time it just acts like its in neutral. I scanned it and the codes I got were
VAT C0502
VAT C0507
PCM P1406

Any help you guys can provide would be great, he's a 17 year old kid and his dad just lost his job so I'm fixing it for free while Im off for school. I just need a push in the right direction as I haven't dealt with any of these vehicles before.

Thanks

 

[dirttymaxx]

if i remember right the vat codes are for the locks and etc the pcm code is what you need to find out about. i know this will make everyone feel like a dumn butt but PCM= power control mod= tranny i dont know where to find the codes list at but thats a little push

 

[c55asleep]

One of my younger brothers friend's tahoe took a crap on him yesterday. He was driving it when it decided to quit putting power to the ground. It will rev up normally and sometimes will creep forward, most of the time it just acts like its in neutral. I scanned it and the codes I got were
VAT C0502
VAT C0507
PCM P1406

Any help you guys can provide would be great, he's a 17 year old kid and his dad just lost his job so I'm fixing it for free while Im off for school. I just need a push in the right direction as I haven't dealt with any of these vehicles before.

Thanks

Have you tried obdii.com to get the codes? I checked quickly and it showed some stuff of the steering wheel and egr system.

 

[RENODMAX]

Yeah I did but I also found speed sensors. If it were a chassis code I would guess its a wheel speed sensor but I wanted to check with people here to see where to start as there's multiple speed sensors

 

[RENODMAX]

Forgot to add its an auto trans 4wd. Doh

 

[THEFERMANATOR]

First question is are you sure of the codes being the actual codes? I pulled up a 98 5.7L tune I have and there is no listing for a P1406 even in it. When I checked what the code is, it is an EGR code according to a generic OBD2 code list I found. And neither of your C codes showed in my ALLDATA either. As for the trans, have you check ed the fluid level yet? Has there been any work done to it recently? Since it's a 4X4, check the transfer case to make sure it didn't get put into neutral. The shift encoder motors on that case are known to fail and pop into neatral. You can unbolt the encoder motor from teh transfer case and shift it manually at the stub shaft to verify if it is that. Also make sure it has fluid in it and that it hasn't worn through the case and leaked out like the DMAX trucks experience. If the transfer case is engaged, then you will need to drop the pan and see if teh boost valve has popped out of the pump housing as I have seen this happen and cause a loss of movement, but this was following some trans work that had been done.

 

[RENODMAX]

I scanned it and those were the codes I got. Has fluid but would not engage from 4wd to 2wd the light on the button just flashes. I've come to the conclusion that its a 97 however.

 

[poweredmotives]

I have a 97 1500 pickup that did that once. it was the speed sensor on the rear output of the t-case.

 

[RENODMAX]

Awesome guys ill give it a whirl. I've never a built anything other than an Allison so I figured I better ask. I'll try what fermanator said then try the speed sensor

 

[THEFERMANATOR]

A speed sensor won't cause it to not move at all as reverse is all mechanical in the 4L60E. And if you unplug the trans connector, it will still give you 2nd or 3rd. The flashing lights on the 4X4 buttons though is a sign that the encoder motor may be malfunctioning though. When it fails the switch will just flash at you as it doesn't know where the shift motor is at. Ran into this with a friends 99 BURB when his failed. We pulled the encoder off and shifted it to 2 high and manually moved the encoder till it was there and put it back on until he could get another one.

 

[duramaxdiesel]

I have nothing to add to this, but man it sure is nice to see people really help out here with detailed answers:thumb:
Nick

 

[RENODMAX]

A speed sensor won't cause it to not move at all as reverse is all mechanical in the 4L60E. And if you unplug the trans connector, it will still give you 2nd or 3rd. The flashing lights on the 4X4 buttons though is a sign that the encoder motor may be malfunctioning though. When it fails the switch will just flash at you as it doesn't know where the shift motor is at. Ran into this with a friends 99 BURB when his failed. We pulled the encoder off and shifted it to 2 high and manually moved the encoder till it was there and put it back on until he could get another one.

So I can pull this off and manually move it to 2 hi and if it works then I know for sure its a bad bad encoded motor. Strange it doesn't flash at me in 4wd. Also what would the symptoms of a vacuum switch be? Thanks again ferm

 

[THEFERMANATOR]

I believe there are 3 15MM bolts that hold the shift encoder motor assembly onto the transfer case. take it off and you can manually shift it with a crescent wrench. Which vacuum switch are you refferring to?

 

[RENODMAX]

I believe there are 3 15MM bolts that hold the shift encoder motor assembly onto the transfer case. take it off and you can manually shift it with a crescent wrench. Which vacuum switch are you refferring to?

I'm going to try that right now. Got a chance to get out from behind the welder. So if this truck moves occasionally very slowly with a lot of rpm you think it still might be an encoded motor? I'm hoping for the kids sake its not hydraulic

 

[RENODMAX]

Well I got there today checked it out and there's a puddle under the t case. I'm going to see if its worn a hole. Where is the most common place for a hole to occur on these?

 

[RENODMAX]

Pulled the little skid plate off, looks like the sealant on the bottom of the case split as it was leaking about a 6 inch puddle just sitting there and the skid plate was FULL of dirt and ATF. There was still a quart and half or so of ATF in the case. I dont know anything about these transfer cases are they clutch or chain? And if so is a low fluid level going to render it useless? Im gonna clean it up pull the case out and make sure nothing is messed up in it. Fluid looked good with no shavings or chunks. After I fill it and put it in I am going to check to encoder motor as well. Ferm if you see this give me a call if you wouldnt mind since you know your way around these guys. 775-848-9769

Thanks
Jordan

 

[RENODMAX]

Pulled the case out, springs for synchronizer were laying in the bottom of the case with a retainer. Reassembled with new springs and resealed, all shifts like it should. Time to pull the pan.