SOLVED!-04 Trailblazer LT 4.2 L no crank - no start

[mrrsm]

Anybody "Shine Up" the motor compartment with any Cleaning Products... or maybe run or spray water under the hood in way that might compromise the Electrical Harness to the Engine and PCM? Now I am not saying that this actually happened but... since your Wife likes this vehicle... perhaps she was trying to make things look nicer under the hood?

EDIT

I never try to use the Expressions "She"... or... "The Wife" in any Pejorative Way....as... I have one myself. But I can say from having considerable personal experience of over 45 years... that when THEY are unhappy... "The Husband" is invariably both the cause...and... the cure.

 

[Rad]

She gets in, fires it up and goes. When something doesn't work, she calls the Husband. This is by far the longest and most troublesome issue I have experienced since I started working on cars around 16 years old. I am close to throwing up the "surrender flag" but not until I check all the grounds. You had recommended in one of your earlier posts to check the grounds on the lower left side of the engine.

I was in fact under the truck when I had it up on ramps and visually checked the engine grounds and checked them for tightness. I didn't break any of them loose (as I should have) since all were nice and clean and tight. But knowing now that a faint ground signal is in fact reaching pin 85 - I have to go there again and check.

Since the PCM is mounted to the engine, I would guess that it gets its ground from the engine connected grounds. When performing the resistance check on PIN 65 (ground) at C2 (as suggested by @coolasice), it measured 0.00 to NEG battery and at the left side fender well ground point. Resistance between the PCM case itself to NEG battery measured 0.75. This may be negligible and acceptable resistance and not the root cause but should probably also be 0.00 resistance.

 

[mrrsm]

Actually... the PCM... as far as I can recall... is held on with some slender bolts that screw inside knurled and threaded Brass fittings that might just be sunk inside some polycarbonate posts on the outside of the similar plastic-like insulated material that the Intake Manifold is made of... But I haven't actually got any lead-pipe cinch proof that these do not in some way manage to go to ground somehow. This is enough to make even the most patient of us edgy...and in truth... to the last man... we really want you to beat this damned "Ghost in The Machine"...FTW...(For The Win...)

 

[Rad]

You are correct. Coincidentally, I just read up on GM PCM grounding.
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?2440-Ground-the-ECM-case-itself
Apparently GM doesn't ground its PCMs directly to metal. But the PCM has to get its ground from somewhere at some point through a wire. But which one and what is its point of origin?

 

[coolasice]

You are correct. Coincidentally, I just read up on GM PCM grounding.
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?2440-Ground-the-ECM-case-itself
Apparently GM doesn't ground its PCMs directly to metal. But the PCM has to get its ground from somewhere at some point through a wire. But which one and what is its point of origin?

The ground you checked, c2 pin 65 goes to the engine block under the pcm. It is the sole ground for the pcm. Can you also check the power lead going into the pcm? C1 pin 20. Check resistance to battery +. Also check for power to c1 pin 19 when key is in run/start positions.

 

[budwich]

Not sure what other circuits switch ground thru the pcm, but maybe you can find one and checks it operation to see if things are different. I know the fuel pump (relay) does not.... it switches voltage. I actually don't know of any others at this point... but maybe some one with more gm knowledge does. Anyways, it may give another data point on a grounding issue... maybe.

PS... maybe the air relay for the SOL system but maybe it doesn't operate til the engine starts...:-((

PPS. the only thing I can see at this point is the check engine light which isn't easy to get to :-(( BUT not sure if this was asked previously, but with your key in on, your check engine light IS ON... right?

 

[coolasice]

Not sure what other circuits switch ground thru the pcm, but maybe you can find one and checks it operation to see if things are different. I know the fuel pump (relay) does not.... it switches voltage. I actually don't know of any others at this point... but maybe some one with more gm knowledge does. Anyways, it may give another data point on a grounding issue... maybe.

PS... maybe the air relay for the SOL system but maybe it doesn't operate til the engine starts...:-((

PPS. the only thing I can see at this point is the check engine light which isn't easy to get to :-(( BUT not sure if this was asked previously, but with your key in on, your check engine light IS ON... right?

Switched grounds. ... injectors, air pump relay, air valve, evap purge, evap vent, shift and tcc solenoids, ac compressor relay, o2 heater circuits, and mil light

 

[Rad]

Thank you guys for not abandoning me on this. Surrender flag in hand but not willing to throw it up in the air just yet. I will go out and check the few things you asked at PIN 19 and PIN 20. @coolasice ( I did check PIN 20 previously and it is definitely getting power).

@budwich - I will double check the "Check Eng light" but I am pretty sure it behaves normally like with key in run, just a momentary illumination along with all the other lights on the dash and then goes out with others.

Will return shortly.

 

[budwich]

Well... it should NEVER go out with key in run with the engine not running.

 

[Rad]

Checked voltage on pins 19, 20, 21 (on C1)
Results:
PIN 20, 12.22 Battery Voltage. Resistance 0.00 w/key OFF. Resistance 0.42 w/key in RUN. Resistance 0.07 w/key in crank.

PIN 19, 12.00V w/key in RUN

PIN 21, 11.97V w/key in RUN

 

[Rad]

@budwich - sorry, mistook "Service Engine soon" light for another CEL light. Service Engine soon light stays on with key in on position. Service Engine Soon and CEL must be one and the same since the TB does not have the "Engine" Symbol.

 

[coolasice]

Checked voltage on pins 19, 20, 21 (on C1)
Results:
PIN 20, 12.22 Battery Voltage. Resistance 0.00 w/key OFF. Resistance 0.42 w/key in RUN. Resistance 0.07 w/key in crank.

PIN 19, 12.00V w/key in RUN

PIN 21, 11.97V w/key in RUN

Voltage with key in crank? Where did you measure resistance from/to?

 

[coolasice]

I have one last test that may help rule out a bad wire. Disconnect c1 from pcm. Remove start relay. Jumper pin 85 to 87 with a suitable wire/object that won't damage the connectors in the fuse block. Next, with key in run, connect test light from gnd to pin 48 on C1 and see if the light illumminates.

 

[Rad]

Resistance checked between PIN 20 and POS Battery terminal as requested

 

[Rad]

I have one last test that may help rule out a bad wire. Disconnect c1 from pcm. Remove start relay. Jumper pin 85 to 87 with a suitable wire/object that won't damage the connectors in the fuse block. Next, with key in run, connect test light from gnd to pin 48 on C1 and see if the light illumminates.

OK...will do and report back. Not sure if you saw my earlier post where I stated that when I performed the test for ground at PIN 85 in darkness with my test light (connected to POS Battery and probing PIN 85) while the wife pushed key to crank, the light illuminated dimly (no where near as bright as when touching ground) but nonetheless, illuminated and stayed illuminated for approximately 15-20 seconds after key was turned off.

 

[coolasice]

OK...will do and report back. Not sure if you saw my earlier post where I stated that when I performed the test for ground at PIN 85 in darkness with my test light (connected to POS Battery and probing PIN 85) while the wife pushed key to crank, the light illuminated dimly (no where near as bright as when touching ground) but nonetheless, illuminated and stayed illuminated for approximately 15-20 seconds after key was turned off.

That's why I said to test the wire with the jumper. See if it lights up normally or poorly

 

[budwich]

OK...will do and report back. Not sure if you saw my earlier post where I stated that when I performed the test for ground at PIN 85 in darkness with my test light (connected to POS Battery and probing PIN 85) while the wife pushed key to crank, the light illuminated dimly (no where near as bright as when touching ground) but nonetheless, illuminated and stayed illuminated for approximately 15-20 seconds after key was turned off.

you need to do a meter voltage check to the point (with key in start)... not a test light. And you need to have the meter touching a known ground (black lead) and the red lead has to be at the test point in question (pin 85). What does it read?

 

[Rad]

Followed your instructions and here are the results:
Test light did not illuminate with contact on PIN 48 (at least I could not tell if it illuminated faintly since it is bright and sunny outside). Repeated test with Digital Meter and checked resistance on PIN 48 with other end of probe on POS Battery. It measured 0.31

 

[Rad]

you need to do a meter voltage check to the point (with key in start)... not a test light. And you need to have the meter touching a known ground (black lead) and the red lead has to be at the test point in question (pin 85). What does it read?

OK...will do an report back in a few.

EDIT - Just so I understand correctly...you only want PIN 85 probed with this test and not jumped (85-87) with POS probe on PIN 48 and black probe on known good ground?

EDIT 2 - Just for thorough clarification, you are saying that I need to do a VOLTAGE check at that point, not a resistance check, correct?

EDIT 3 - @budwich - are you referring to the test I performed last night in darkness or are you referring to the instructions provided by @coolasice? I don't want to confuse the two. Thanks!

 

[coolasice]

Followed your instructions and here are the results:
Test light did not illuminate with contact on PIN 48 (at least I could not tell if it illuminated faintly since it is bright and sunny outside). Repeated test with Digital Meter and checked resistance on PIN 48 with other end of probe on POS Battery. It measured 0.31

I'm almost certain there is a bad connection here somewhere, the light should have lit up if the key was in run.. just out of curiosity what brand/model meter?

 

[budwich]

go back to the posted diagram.
there are no relay pin numbers identified there. You need to probe the one on the coil that is going towards the pcm... whatever pin number that is. What does it measure when key is in start.

 

[Rad]

you need to do a meter voltage check to the point (with key in start)... not a test light. And you need to have the meter touching a known ground (black lead) and the red lead has to be at the test point in question (pin 85). What does it read?

I'm almost certain there is a bad connection here somewhere, the light should have lit up if the key was in run.. just out of curiosity what brand/model meter?

The meter is just a basic digital multimeter (not a fluke). Made by Leviton

 

[coolasice]

The meter is just a basic digital multimeter (not a fluke). Made by Leviton

What setting are you using for resistance measurements?

 

[Rad]

go back to the posted diagram.
there are no relay pin numbers identified there. You need to probe the one on the coil that is going towards the pcm... whatever pin number that is. What does it measure when key is in start.

I added the PIN numbers to the picture as identified by @MAY03LT in his video. I take it you mean to probe PIN 87 which is HOT at ALL TIMES (BOLD is Edited)

EDIT - 86 gets hot in RUN POSITION only

EDIT 2 - 85 gets the ground signal from the PCM

If I jump 86 to 30, or 87 to 30, engine will crank. If wrapping a thin wire around relay PIN 85, relay installed, key in run, and touching the other end of the wire to ground, engine will crank.

 

[Rad]

What setting are you using for resistance measurements?

2K

 

[Rad]

go back to the posted diagram.
there are no relay pin numbers identified there. You need to probe the one on the coil that is going towards the pcm... whatever pin number that is. What does it measure when key is in start.

@budwich - can't do that test right now, wife taking a nap with my grandson. I need her to turn the key to start/crank to perform this check.

 

[coolasice]

2K

Set your meter to the lowest setting (200) and test the resistance from 85 to pin 48 again... something is amis

Edit: your test light did illuminate from gnd to 87 correct?

 

[mrrsm]

If it comes to this...

http://www.ebay.com/itm/TRAILBLAZER...ash=item2ee81a8922:g:MEoAAOSwkNZUlyV~&vxp=mtr

More here...

http://www.ebay.com/sch/i.html?_fro...RS0&_nkw=2004+trailblazer+fuse+block&_sacat=0

 

[Rad]

Set your meter to the lowest setting (200) and test the resistance from 85 to pin 48 again... something is amis

Edit: your test light did illuminate from gnd to 87 correct?

Will do. I edited my post with picture attached to read that 87 is hot at ALL Times (no key turn required)

EDIT: Added - performed resistance check between 85 and PIN 48 at lowest setting and the reading was:

Initial contact reading 01.5 which stabilized at 00.5

 

[coolasice]

Will do. I edited my post with picture attached to read that 87 is hot at ALL Times (no key turn required)

EDIT: Added - performed resistance check between 85 and PIN 48 at lowest setting and the reading was:

Initial contact reading 01.5 which stabilized at 00.5

My bad, I meant 86 not 87

 

[Rad]

My bad, I meant 86 not 87

86 lights up when key is pushed to crank/start

 

[budwich]

I added the PIN numbers to the picture as identified by @MAY03LT in his video. I take it you mean to probe PIN 87 which is HOT at ALL TIMES (BOLD is Edited)

EDIT - 86 gets hot in crank position

EDIT 2 - 85 gets the ground signal from the PCM

If I jump 86 to 30, or 87 to 30, engine will crank. If wrapping a thin wire around relay PIN 85, relay installed, key in run, and touching the other end of the wire to ground, engine will crank.

You keeping making assumptions about what the circuit is doing.
85 gets a signal from the pcm... it could be anything.

Anyways, I would like you to confirm / measure the votage where pin 85 would be in the relay socket...red probe there (or on the wire that you were placing there) and black on a known ground. what is the voltage reading with key in start (PS. thank your wife for us for helping us... ).

 

[coolasice]

You keeping making assumptions about what the circuit is doing.
85 gets a signal from the pcm... it could be anything.

Anyways, I would like you to confirm / measure the votage where pin 85 would be in the relay socket...red probe there (or on the wire that you were placing there) and black on a known ground. what is the voltage reading with key in start (PS. thank your wife for us for helping us... ).

No assumptions here... I'm following the service manual... 85 is an open connection until the pcm closes the "switch" to ground. Nothing more.

Now 87 AND 86 are always hot (+12v) with key in run, so we bridge 86 or 87 to 85, we then have +12v at the other end of 85's wire (c1 pin48), right? Connecting the test light between the end of the wire and ground completes the circuit and voila... we SHOULD have illumination... if not there is a break/poor connection... now since the light worked fine at 86 AND 87... it must be a bad connection between 85 and it's endpoint (c1 pin 48 at pcm)

 

[Rad]

Checked for voltage at PIN 85 with red probe and black probe on good ground. Result: 0.00 Volts

I edited the picture post once more: PIN 86 is only hot in only in RUN and measures 12V. In crank, it measures 0.00.

 

[coolasice]

86 lights up when key is pushed to crank/start

Checked for voltage at PIN 85 with red probe and black probe on good ground. Result: 0.00 Volts

I edited the picture post once more: PIN 86 is only hot in only in RUN and measures 12V. In crank, it measures 0.00.

So does it or doesn't it have power in crank?

 

[Rad]

No assumptions here... I'm following the service manual... 85 is an open connection until the pcm closes the "switch" to ground. Nothing more.

Now 87 AND 86 are always hot (+12v) with key in run, so we bridge 86 or 87 to 85, we then have +12v at the other end of 85's wire (c1 pin48), right? Connecting the test light between the end of the wire and ground completes the circuit and voila... we SHOULD have illumination... if not there is a break/poor connection... now since the light worked fine at 86 AND 87... it must be a bad connection between 85 and it's endpoint (c1 pin 48 at pcm)

When checking resistance between 85 and PIN 48 without battery, I recall it measuring 0.00. But with everything connected and performing the check last night in darkness (just to see if anything reached 85 - was looking for a NEG signal) the test light illuminated (green) weakly. So it is getting a ground signal from the PCM. That fact is proven. So where is the breakdown in good connectivity?

There was some resistance measured between the PCM and ground (0.75). If the PCM gets its sole ground from PIN 65 on C2, it may be worth taking a look at the ground point/source of origin to the PCM wherever that is. CoolasIce, you stated the PCM ground is below the PCM on the engine (which I assume travels trough a wire). Does your service manual show the ground point number?

 

[Rad]

So does it or doesn't it have power in crank?

86 did not show power in crank, only in run

 

[coolasice]

86 did not show power in crank, only in run

You said earlier it had power in both run and crank...


without power during crank it cant turn on the relay

 

[Rad]

I will double check...

 

[budwich]

Checked for voltage at PIN 85 with red probe and black probe on good ground. Result: 0.00 Volts

I edited the picture post once more: PIN 86 is only hot in only in RUN and measures 12V. In crank, it measures 0.00.

Just to be clear, the pin 85 test was with key in start... right?