Newbie: 2004 GMC Sierra P0650/P0496 Oil Pressure Gauge Malfunction?

[NastyBuzzard]

Just traded my 99 Z28 NBM 6speed convertible for this truck.

2004 GMC Sierra Crew Cab Short Bed Z85. Truck has 128XXX miles on the body but dealer replaced engine at 78XXX. 5.3/4L60E 3.42 peg leg..

Pics are from the previous owner, I haven't cleaned it up yet for pics.

















It has a couple issues.

Has codes:
P0650 MIL Fault?
P0496 unwanted vacuum? Bad purge solenoid?

To start with the engine oil pressure gauge is acting crazy. With ign on, eng off the gauge pegs to 80. When you crank engine it pegs to 80 and sometimes will stay at 80 or drop all the way down to 0. Any ideas if its oil pressure sending unit or stepper motor in the cluster?

Previous owner said that when he fills up the truck and goes to leave station the truck is hard to crank for a few seconds but will eventually start. Starts fine all other times.

Any ideas fellas? Other than needing new tires (tires for 20" rims are expensive as hell!!), the truck seems great! Eng/trans is so clean you could eat off of it!!

Also thinking of getting rid of the step bars and the bed rails, maybe even the bug shield. Thoughts?

[Sillyoldman]

Just curious what went wrong with the original motor? It was just a baby. Great looking truck though.

[NastyBuzzard]

Originally Posted by Sillyoldman

Just curious what went wrong with the original motor? It was just a baby. Great looking truck though.

Thanks!! I think so too. I am hoping to make it better!

Previous owner said that it had noisy valvetrain that dealership kept waving off and then the cam got ate up and they had to replace it. I have the dealer invoice where the engine was replaced and everything.

[NastyBuzzard]

Another thing I just noticed. While driving down the hwy it all of a sudden started blowing hot air out of ds only. It did this until I put it in neutral, shut it off and started it back up. As soon as I did that it started blowing cool air like normal.

I had ac/heat off. The fan was set to 0. Any ideas?

Also anyone ever seen a crew can sierra Z85? Mine has the decals and rpo code but I can't find another one like it online anywhere. Previous owner said it was special ordered.

[NastyBuzzard]

New oil pressure switch/sensor fixed my pegged out oil pressure gauge problem.

I deleted codes friday and have driven it some and no codes have come back, yet.

However, it does randomly keep blowing hot air through the drivers side vent and doesnt stop until you restart the truck.

[1FastBrick]

P0496 could explain your hard start condition after a fill up. It's usually a Purge solenoid but could also be a plugged canister. It Requires proper diagnostic to determine if that's the route cause. See here... http://www.obd-codes.com/p0496


P0650 Is a fault with the MIL Circuit. It's possible the cluster it self has an issue. If the oil pressure gauge goes haywire again It could be a sign the Cluster is the issue. Cluster usually have the stepper motors go bad and occasionally the solder joints can crack on the board causing other issues . http://www.obd-codes.com/p0650


Your hot air issue is usually the blend door motor. It's common on these trucks.

You also need to verify that the AC system is working properly and that you don't have a low charge or a bad compressor. You need to go to someone who specializes in this. It requires AC gauges, system knowledge and a specialized factory style Scan tool or equivalent to monitor data. It can also be used to test the Actuators in the system Via Bi-directional controls.

[NastyBuzzard]

Thanks Fast!

So far I have changed the purge valve on intake with a spare I had, put a new oil pressure switch and replaced the blend door actuator with a spare I had.

The results so far are no codes as of yet. Been driven about 50 miles. After I changed the oil pressure sensor I got my oil pressure back! After changing the blend door actuator with a spare I have yet had the issue to reoccur where it randomly blows hot air out the drivers side vents.

Next is all new brakes, park brake drum, and probably atleast one new rotor and the others turned.

Then service engine, check plugs and all.

A big pain in the ass is the shift linkage/cable. Problem is that some times it is very tricky to get into park. Shifts everywhere else perfectly from R to 1. But when you try and put it into P the lever will go but it's like it's in limbo and rolls. The P on the dash doesn't light up and if you touch it the slightest it falls back into R. I basically keep having to move forward or backwards till I get the sweet spot where it will go into Park.

From research only thing I can find is to replace the whole cable.

[1FastBrick]

It may need to go to a professional for the AC issue.

I have never heard of the parking cable issue you describe. I would suspect either something is not aligned correctly or some one was inside the transmission.

You can chalk the tires up and pry the cable off the shift lever on the trans while it's in park. If there is a misalignment, something is either wrong with the cable or it needs an adjustment. I am not sure if these have any room to adjust them like older models did. You can also align the sensor so that P light's up. It may be misaligned.


Personally I like to replace my rotors in pairs. It keeps everything wearing properly.

[structures]

I have an 03 Z71 with 106k miles. I've owned it since it had 20k. I've had a lot of the issues you describe.

The shift cable issue I had after I loaded the back full of firewood (bump stops touching the axle) then drove it out of a winding trail. Torquing and twisting the truck. Long story short there is a plastic sleeve the gives the shift cable support at the trans shift linkage. The plastic sleeve was broke. The shift cable has a factory splice on the lower side of the cab. So I bought a whole cable but only replaced the lower half.

Had a '96 chevy 1500 and did a similar thing.

[NastyBuzzard]

Originally Posted by structures

I have an 03 Z71 with 106k miles. I've owned it since it had 20k. I've had a lot of the issues you describe.

The shift cable issue I had after I loaded the back full of firewood (bump stops touching the axle) then drove it out of a winding trail. Torquing and twisting the truck. Long story short there is a plastic sleeve the gives the shift cable support at the trans shift linkage. The plastic sleeve was broke. The shift cable has a factory splice on the lower side of the cab. So I bought a whole cable but only replaced the lower half.

Had a '96 chevy 1500 and did a similar thing.

Do you remember what part#/brand or where you bought that cable from?

I jacked the truck up and went and looked at it and basically where the plastic piece pulls through the bracket on the side of the trans, it has two little ears that stick out to hold it into place where the C clip thing is, well one of those ears has been broken off. Someone ziptied it to make sure it doesn't fall out but apparently it needs to be replaced.

Supposedly the previous owner just had trans serviced with a corvette servo installed. I know from experience dropping that pan is kind of a pain in the ass so they may have messed up the cable when they did that. Not 100% sure.

I do have a 2001 z71 silverado I have for a donor for my ls swap in my 87 gmc sierra 4x4 so may rob the cable off of it and try it out.

[structures]

I ended up buying that cable from the dealer. It's been a while. Don't know why. You might be able to find just the lower half online.

Dropping the pan was a pain for me! I just got done with a trans oil change on mine.

[NastyBuzzard]

Originally Posted by structures

I ended up buying that cable from the dealer. It's been a while. Don't know why. You might be able to find just the lower half online.

Dropping the pan was a pain for me! I just got done with a trans oil change on mine.

It can be done trust me. I just use a long flathead screwdriver to pry against that bracket. First time I did it was a pain and when I put it back on I forced it a little to hard and broke a solenoid. Now I am a lot more careful and pay more attention.

I am thinking about adding the deeper pan & filter to this 04 as well as an external trans cooler.