Dtc 46

[Robyn]

Well now

The dually is coming along great and the beast is just such a joy to drive.
The feel of power is, well, Ummmm I like it. :D

Last night we headed off to the outlaws for a few minutes and Pat was driving, Im off in la la land and pat says hey, the check engine light is on. :eek:
The rig is running fine so at the next stop we shut the engine off and did a restart and all is well.
I pulled the code when we got home and it is a 46. Mil light circuit fault.
I dont think I have ever seen that one.
I somehow suspect its all related to a voltmeter issue I have been having.
I have been working on the system grounds and have some of the stuff checked but not all of it.

I have this thing about seeing the SES light, it sort of brings the fear to me that A pilot has when that voice booms in the cockpit, "Stall Stall Stall Stall" OH **** now what :eek: :eek: :eek:

The truck had been outfitted with a load of extra equipment and I suspect something has or was disturbed from the way the factory had it.

Any input from someone who has seen this code would be appreciated.

Thanks folks

Robyn

[gmctd]

Two failure modes -

- circuit is shorted to ground = no MIL lite

- MIL lite is blown = no MIL lite

- circuit is shorted to +12v = no MIL lite

(Well, that's three - so, disbar me!)

PCM monitors the ckt for the voltage level according to demand, starts complaining if it ain't right.

[Robyn]

Well now
The light came on and stayed on. Shut the engine off and then the light went away and stayed off for the remainder of the eavenings trip.

Light on, (BULB Must be ok)
If it was shorted either to ground or to 12V how could it come on??

Still thinking the dash grounding may be goofy???

Thanks

Robyn

[DmaxMaverick]

Too funny!

I think it's ironic........Lil' "missy 'don't need no steeenkin' technology' goodwench", with a lamp, telling her the lamp that's supposed to come on when the technology goes wrong, is on, telling her the lamp isn't working. Did I get that right? ((I meant that in the most affectionate way))

All you need is some gages and a piece of black tape. As long as it's running, and all the gages are in check, put the tape over the lamp. Other than that, the instrument clusters are, well....a cluster....... Nice when they work, disposible when they don't. The first warning of a problem is a real good indicator to start shopping for a replacement. The older ones could be jumpered and bypassed (the PCB), but the later models are not so forgiving. Problem is, the '46' will indicate a failing PCM just about as often. But, there's a lighter side....It's probably just a ground that ain't happy.

Good luck!

[gmctd]

Yep - this truck's smarter than her other one, and it obviously has her number, eh?

But, yeah - it's prolly grounding, where the intermittent event occured just as PCM was running it's housekeeping routines, which tripped the MIL.

Or, could it be a haunted truck - the coloring and shading sorta reminded me of Casper, the friendly gho......ummmm - never mind!

'Scuse, me - gotta go find some salt to throw over my shoulder..........

[Robyn]

Robyn trots off to the parts store to buy a package of grounds and a new PCM.
OH MY GAWD maybe I need to yank up the carpet and make sure there are no skeletons hiding in the corners.

Last night I replaced both battery grounds as well as checking the harness grounds on the back of the engine.
I added an extra braided strap from the firewall to the engine.

This improved the voltage reading at the gauge.
I think this weekend I will yank the front of the dash off and peek around taking a look at the under dash grounds.

I love the humor guys.

Definately gotta love this place.. :D :D :D

Robyn

[twaddle]

Hi Robyn,
Are the two batteries grounding on to each side of the engine only?
On my 96 Suburban I added extra ground cables as you are doing but also linked the negatives on each battery with a H/D cable. I didn't like the idea of the engine and inner fenders being the only way the two batteries joined up.

I also found one of the heavy duty ground cables had swelling under the insulation which turned out to be the dreaded green stuff, verdigris, and this was almost 15 inches away from the battery.

Good luck and I think the Guys are just jealous of the new truck.

Jim

[Robyn]

Jealousy, Here at TDP?? :eek: :eek: :eek:

Nawwww they are just having some fun is all.

I have made such a fuss over hating all the computer stuff, then buying a 91 with very little of it and then selling it and buying the 95 with the computer again.

One thing about this truck is that its been messed with by a lot of folks and who really knows what all they had their paws on when they wired in the extra radios, TV and lighting goodies.

Too bad that the factory does not put a few key switched terminals in the main relay box that could be accessed easily. This would keep a lot of the fools from screwing things up with the little crimp on connectors that uhaul sells. GRRRRRRRRRR :mad:

Just my trun in the barrel is all.

I think the next session is going to be to pull the dash cluster out and have a look see at the wiring and the connections on the mylar trace panel.

Later

Robyn

[gmctd]

I'm jealous.........

[Robyn]

Robyn sends GMCTD a bouquet of flowers and a cyber hug. :D
Also a fresh clean hanky to sop up the tears :)

Robyn

[Robyn]

Well some much needed luck may have presented itself.

Coming down to the shop a bit ago I hit a bump in the road as I was braking for a corner and the volt meter went all the way up to 14 where it belongs and stayed there.
I noticed it just as it happened and watched it for a fee seconds, a good swat over the top of the dash sent the gauge back down to around 12 again.

Hmmm good bet the issues are in the dash cluster/printed circuit unit.
Been there done that before just not with this late of a rig.

I think before I rip it apart I will see about finding a replacement unit with .lower miles on it and possibly in better condition.
Very well may be able to fix this with some contact cleaner and a little fussing too.

I am not sure how the ground setup is on the circuit panel but I suspect all the grounds or at least those for gauges are bundled and feed though one tap off of the mylar panel.

Usually the lights are grounded seperately and then the gauges by themselves and the tach and fuel gauge by themselves.

If the panel ground is the issue then the MIL light would be effected and most likely this would be the cause for the code 46 and the volt meter issues.



We shall see

Robyn

[gmctd]

See? Toldja...........

[Robyn]

Yup, very good guess

I just hate to start thrashing on stuff untill I at least have something other than suspicions .

Beings the gauge responded so quickly to a rap on top right above it I am going to venture a guess that is either an issue with the gauge or possibly the plugin connector for the whole cluster.

Right now my plan is to pull the sucker apart and have a look see.
Unfortunately its raining today and I am not going to sit out there in the rain with the door open ripping a dash apart.

Too much crap in the shop to get the beast indoors so Oh well.

Funny thing is the only time I can get this thing to show the full charge at all is when the rig is first started and for a few miles of driving it might do something. After the rig has been run for a while the gauge settles down toward the 12V mark and stays there.

Maybe a voltage regulator in the printed circuit panel??? or current flow over time causes the connection to get more flakey.

Gonna just have to rip it apart.

I drove the truck aroound a lot yesterday and then last night Pat drove us home from the Outlaws and the check engine light came back on.

HMMM does not like Pat me thinks. I get in behind the wheel and the sucker goes out and stays out.

Another question was rolling around in my little gourd.
If it were to turn out to be the PCM and I replace the unit, does the running parameters such as TDC offset have to be reset or does that follow the Prom thats in the rig now??
I have not torn into the thing but I assume it has a Heath diesel chip(OR other) in it along with the Turbo master.
The sucker will push 13-14 PSI at times and never set off a code so it must have something in there other than stock.

Cooments???? :)

Robyn

[gmctd]

Guess? What guess? We don' use no steenkin' guesses 'round here!

Replacement OBD1 PCM will require timing\TDCO reLEARN - then you'll need to drive it around normally for about 15mins to relearn driveability parameters.

Cooments - yeah, I agree - appears the truck definitely don't like Pat!

[Robyn]

Well lets hope we dont need to do that.
I dont have access to an OBD1 scantool or any who does.
And I am not real hot on paying the dealer to screw it up for me.

Going to get a low mile cluster from a local bone yard and see where we go from here.

We were out today cruising around doing some Geo Caching and the sucker was behaving itself all day. The volt meter even came up to 14 on several occasions but the slightest tap on the cover would send it plumeting.

I dont think there is any issues with swapping the clusters. I know the radios have an anti theft code that has to be input if they are replaced or moved.
Not sure about the gauge cluster though.

Robyn

[gmctd]

The inst cluster is pre CAN-buss, so no problemo, there

If ya got a hankerin' to play around with OBD1 scanning, check out Swedeburb's GMCTDScan at ENGH Motors - got a free version with instrument panel and reads most sensors, and the Tech upgrade does everything the Tech2 does, for about 1/50th the price - loads into your laptop pc.

Try it - you'll like it............

[Robyn]

I am going to have to get that program
I have a nice lap top that I use for various other things and it would be cool to be able to do the diagnostics the right way.

I had an auto Xray unit that was a nice tool but it quit so that was that.

I just sold my 86 Dually this eavening and got my asking price on it and cash to boot.
I can justify a few things but most of the dollars have to go back into the bank.

I decided that whatever I bought could not cost more than what I could sell the 91 and the 86 for. I think I will come out about $400 more than what the 95 cost me so I am good to go.

Thinking about maybe a new dash cluster but I can only imagine what they cost.

A good used one here is going for $125

Later

Robyn