DLC No Go..01 'Burb.

[Arnold]

My scanner says it can't connect..(make sure the ignition is on)
 Scanner works fine on my g/f's 01 GMC truck.

  About a month ago the lo fuel light came on..stayed on..I put some of that GM gas gauge float contact cleaner stuff in. Appeared to work.
Then I took it to a garage I trust. They looked..wiggled..for a while.Could not find anything wrong.

  2 days ago..start quit..start quit..start quit. Started but the battery light was on.Rev it up and it goes out. Voltmeter looks normal. Load..discharge..start it up..charges.Then EVERYTHING was ok. THEN
the security light came on..and stayed on.

 Yesterday..starts normally..message centre lights. Flashes. Lo fuel,then batt. then service 4wd,then security. Abs light comes on slowly..glowing..
gets bright..then dims and goes out.

 Today the air bag light comes on too. (4wd works.)PLUS now the gas gauge and the temperature gauge go on and off..pulsing.

  Truck runs great..(380  hp works just fine ) EVERYTHING works just fine

  I am busy right now and was just going to take it in when I get time
a good over an hr drive..and that garage is BUSY!!

 I would like to take a quick look when I get a second.

  ANY help/ideas as to where to START to take a quick look would be
greatly appreciated! THANKS.

  I am sortta guessing..bad igniton switch?

  I told my g/f and said that it seems to work fine when I take it out and put the boots to it. Gotta admit..it DOES go pretty good She says it is just an old cop car and as long as it goes "Zoomy" not to worry about it HAHA

  Thanks!

[phat46]

I had some weird lights come on, like the security light, and I don't have the security system in my truck, when the battery was about to die. It died the same day and I replaced it and all was well.....but that was on a Dodge.

[Arnold]

I had some weird lights come on, like the security light, and I don't have the security system in my truck, when the battery was about to die. It died the same day and I replaced it and all was well.....but that was on a Dodge.

  Thanks..I too have had some very weird stuff when a battery goes South. I guess first I have to see if it is getting power at the DLC

[rooster]

Maybe the grounds!

[wayne petty]

quick and almost easy tests.. to see if its the ignition switch...

disconnect the battery...

operate the key from off to start and back off about 50 times...

reconnect battery...  attempt to start...

why.. the music box of an ignition switch contacts get dirty and corroded... without current.. they might make better contact... this has worked on corvette C5 and C6 models to see if the ignition switch is failing...

the ignition switch wiring plug is accessible under the dash with a test light.. please don't probe the TINY wires or the YELLOW harness.. yellow harness  is the AIR BAGS..

go for big colored wires ..  probe.. watch light as you rotate key from off to ON to crank. and back to ON...

PS.. on most GM trucks... you will need external torx sockets.. either in an E4 or E5 size...

harbor freight stores had a nice set of deep external torx for like 8 bucks..  but they are not online .. sizes E4 thru E12.. not the E 8 and Up.. that set won't get the column shroud off .. nor will it get the turn signal switch or the ignition switch off...

to remove the ignition lock cylinder..  disconnect the battery.. turn all the way to the cranking position and depress hidden button with tool to remove it..

if you need to replace .. ignition locks come UNCODED...

no pins or springs...  there is a reason for this.. as if you have to change the key combo.. you can use the uncoded cylinder to start the truck. with the old key.. shut it off and swap keys and restart to get the truck to learn the new key RFID signature..  after you have introduced new keys.. then you can have the lock smith put new pieces in the lock..

if the engine starts and dies..  look over and see if the security light is flashing..  if it is... hook up a set of jumper cables with the other car idling.. the truck ignition key turned on..  or a battery charger to prevent the voltage from dropping... after the key has been on for 10 minutes.. yep...  the security light will flash... the truck will now start ONCE..   there is more to the programming..  but this defeats the 10 minute lock out just in case..  you only get one try ever 10 minutes.. to program new keys without old ones.. .. this takes over half an hour with your stop watch..  battery voltage dropping can cause the system reset to fail..  

i have also had TERRIBLE ISSUES on these trucks with the FUEL pump relays and the 3 wire oil pressure switches..

get into the relay box.. pull the fuel pump relay.. i can supply a link to the owners manual if you don't have a sticker or a owners manual to identify which one..

remove relay... gently remove the cover...  on a towel.. remove the tiny spring.. work the braid over the side of the lever.. now you can slip the lever out carefully..  clean the contacts.... burnish them with a screw driver or a small file tip.. reassemble.  insert bare frame relay into the socket.

have a friend turn the key on.. does the relay close for 2 seconds then open when you don't crank the engine??
and close when you crank the engine??

when you manually close the contacts.. does the truck start?? when you have a friend cranking it.??

the 3 wire oil pressure switch and the fuel pump relay are wired in parallel... both have to be working to actually supply enough contact area for the fuel pump .

when the oil pressure switch contacts fail.. the current is all routed thru the fuel pump relay and the contacts take a beating and the relay socket terminals melt..  

please check for insertion force on the relay socket terminals.. a TINY tipped carbide scribe can be used to lift the tongue of the relay socket terminal to restore grip on the relay terminals. .

if you have one of these.. you can also monitor the fuel pump operation..  as the fuel pump fuse is AFTER the relay and oil pressure switch.. so unplug the fuel pump fuse.. move it to the side of this amp meter connector.. plug this in and monitor the amp draw of the fuel pump .. right around 7 amps is acceptable..  more than about 7.5 amps is getting iffy...  perhaps a bad fuel pump or a dirty fuel filter..

http://www.harborfreight.com/20-amp-automotive-fuse-circuit-tester-67725.html

.

[wayne petty]

if you want to check the grounds.. and you have a digital volt meter... always a good idea...

you can test them while cranking..

1.   positive battery post to the negative battery post..


2.. negative battery post to the engine block while cranking..


3.. negative battery post to the body while cranking..


4.. engine block to the body while cranking..

post results.. this might take longer to write them down than it does to run the test..

here is what your battery cables might look like...

http://i1207.photobucket.com/albums/bb476/waynep712/99chevypu53singlebattery140AMpalt_zps1f3c799c.png


ground locations are at 22,  5 and down on the front passenger side corner of the block...

body to frame grounds are under the cab at the passenger side front cab mount..  

engine to frame grounds also on the frame rail near where the mechanical fuel pump would be..

positive  side places to clean...  4, 3 & 27,  19, 20

[Arnold]

Thank You Very Much For The HELP :!:   ALWAYS APPRECIATED

 I checked the grounds at pins 4,5 of the DLC and also the voltage at 16.
 (My scanner does work on another 01 3/4 ton GMC plus my other car)
 Batt. voltage is good. Drops under load,climbs back when started.
 (At the batt. and with my meter)(( the same with the dash gauge))

  Thanks Wayne for the ignition switch check! I will try that.

  I get the sneaking suspicion that this is not..either..the right key(worked fine for almost a year so far?)
or it is not coded. It does not look right. This is a cop vehicle..and I remember from my years in the taxi business(almost all cop cars become taxis here) that they used to make cop cars up in batches. They * around with ALL the cylinders so that ONE key worked ALL the cylinders in iirc 6 cop cars.This was for emergency purposes so the cop could open/lock the cars,trunks,use the car at iirc 6 vehicles at the detachment
with only 1 key.

  Thank you again Wayne for ALL the extra info you provided me with :!:  

  This is my back up vehicle..and we are expecting some severe storms for the next few days and I have too much stuff in my shop to get it in Like that is a surprise :oops: SOoo I will have to check it out
outside.

   Thanks again Guys...

[papastoyss]

Try checking all your fuses w/a test light. On imports I have found a blown fuse that couldn't be seen by normal eyesight killing power to the ecm causing a no comunication message on a scanner. Check engine light didn't work due to this.

[rooster]

What kind of car you working on?

Maybe wiggle the harness's around while someone else watchs those dash lights!

Food for thought

&feature=fvwp&NR=1

[rooster]

Try checking all your fuses w/a test light. On imports I have found a blown fuse that couldn't be seen by normal eyesight killing power to the ecm causing a no comunication message on a scanner. Check engine light didn't work due to this.

I'll throw this in with what you have allready said!!

[Arnold]

Thanks again guys

 I did pull out all the fuses..they all looked ok. No..I did not check them..
or power to them or the block..I will do that next.I would have then but rain was imminent.

 When the lo fuel light came on..AFTER I thought the GM gas gauge fix in a can had worked?(maybe it did) I had a garage that I trust take another look too.They did a pretty thorough wiring/harness/wiggle test.
 That was 6 weeks ago..ALL was fine..now this.

  We have another 2 days of storms here..so can't look at it again yet

[wayne petty]

gas gauge issues??

don't forget that the fuel pump harness is grounded to the top of the frame rail ... with a nut and bolt that can get corroded..




there have also been issues with the connectors on the end of the chassis side of the fuel pump harness...

if the ground on the front lower corner of the block.. passenger side.. is loose.. dirty.. caked with oil or other..  ground issues will happen...

print what i posted above.. when it stops raining.. go thru it step by step...

[Arnold]

Thanks again for all your help guys

I got a bit of a break from all the storms lately.

Another little weird thing happened..it would shift into all ranges EXCEPT
lo range?

I went over the fuses,panels..wiggling..all seemed ok.
I then pulled off the LOWER cover for the fuse panel in the engine compartment
to do some more wiggling.
I was able to move the short cable at the end where it connects to the panel from the positive  battery.It wasn't really loose..just not tight enough. When I did this there were ALL kinds..lol..of noises..relays etc.
This made the instrument panel,gauges,message centre go REALLY CRAZY LOL..I thought it was crazy before haha.
  I could not really tighten it.   Wtf? The end of the cable where it attached to the fusel panel LOOKED like it was just a conventional cable end with a hole in it for a bolt/screw etc to connect.There was some sort of a nutsert thinggy behind AND in it? I had to push the flat end of the connector down onto the mount on the fusel panel tight AFTER I had fully loosened this bolt THEN instal and tighten the little bolt. Whatever? This looked stock.
This thing ain't designed to come loose. Don't know how it did?
 After this the thing would barely crank. Took quite a few times for it to start. Then it would not idle. Probably re-learning.

 Took it out for a spin..I really love driving this thing In small doses. ALL seems well now.
 My code reader works on it now.

  Thanks very much again for all your help guys

  I will go over all the grounds etc., at a later date

[wayne petty]

please run the voltage drop test before you pull away from the yard...

if that cable was loose... or other cables.. you could have an issue with the alternator being damaged... might not be putting out enough current because of damaged diodes from the OPEN circuit attempts at charging...

this test can be done in under a minute...  and may save you a LOT of money in towing... and parts replacement costs..

[Arnold]

Wayne..I had done those tests. THANKS!  They are within specs.

When I bought this vehicle it had a new alternator on it..the seller said it was not cheap! No I guess it was not. Police Suburban alternator.

I have not driven it that far.

Guess that bad connection is where the first alternator went before I bought it.

GLAD I was not alternator #2 :oops: