No crank no start! Help!

Tanka4ever

Member
I'm hoping to get May03LT in on this, since most of my diag was from his posts and videos, and everyone else as well!

Long time lurker, first time poster. Let me see if I can get everything in one post.

2003 TB i6 4.2 4x4 ext. No crank no start. Changed ignition switch and performed PassLock relearn. Successful relearn but no change. Checked voltage of +12, 12v on run, 12v on crank, white, pink, red, red/white, and yellow. All +12v in keyed positions. Ruled out ign sw.
No dash indicator under the PRND321. Letters come up but nothing to tell what gear it's in. Carefully replaced PNSS (thanks for the glue, GM!) and checked voltage on ground and two pinks on the 7-pin connector, with voltage in keyed positions. Did not attempt to jump the two green signal wires to try to start it. Still no indicator dash.
Checked every fuse in both engine and cabin boxes. All fuses have voltage and tolerable resistance (>.2). All fuses good. Double checked tbc fuses 1-5. All good.
IC gauges and lights all come on... With the exception of "service engine soon". It never, ever, lit up. All other lights come on. Gauges seem to respond to key on/key off. Only gauge that reads anything is voltage. I think the gas gauge works, but don't know because I'm not putting gas in a truck I can't get to start.
When key turned to crank, can hear the RAP relay in cabin fuse block click, cannot get starter relay in engine box to engage, after replacing with known good. Jumped starter relay pins 87 (ign A +12v) to pin 30 (sig to starter) and the engine rolls. Rule out starter.
Checked the 3 connectors on the PCM. No signs of corrosion or loose connection. Checked engine block ground, driver fender ground, checked splice block at driver knees behind the dash, checked splice block beside engine fuse block. No signs of corrosion or loose wiring.
Try to connect an OBD2 reader to data port. No comm. Then tried with a Launch CRP129X and got the beautiful U1000. Only code stored in the computer. It read the SRS and the ABS modules fine.
All this was done with an AGM battery with a trickle charger, 12v 2a current, to keep the battery well alive and healthy.

Please folks. What am I missing?! I'm ready to set fire to this thing, and it's my father in laws!
 

TJBaker57

Well-Known Member
You may need to go a little deeper checking status' at fuses like the crank fuse among others. It is not uncommon for these trucks to have power at the fuse test points but have bad connections in the fuseblock itself. My 02 TrailBlazer had random starting issues (no cracnk) intermittently when I got it. One of my issues was I had power TO the crank fuse but it had a faulty connection where the fuse plugged into the fuseblock so that 12vdc occasionally went no further than the fuse!

Do you have the wiring diagrams yet? These are not a luxury, they are essential to this type of issue. They can be downloaded from the link in Mossemans signature.
 

Mooseman

Moderator

budwich

Well-Known Member
You say that the check engine light never lights.... but is that correct? you never see it coming on during the "check bulb" sequence at the very start of the key on sequence.... but all other dash lights light? Further, IF it lights during the "bulb check" stage but goes out with just the key on, you have an issue with the PCM.... which is somewhat likely since you also can't seem to communicate with it... but do the simple key on check first and go from there.
 
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Tanka4ever

Tanka4ever

Member
You say that the check engine light never lights.... but is that correct? you never see it coming on during the "check bulb" sequence at the very start of the key on sequence.... but all other dash lights light? Further, IF it lights during the "bulb check" stage but goes out with just the key on, you have an issue with the PCM.... which is somewhat likely since you also can't seem to communicate with it... but do the simple key on check first and go from there.
That's correct, Bud, and I'm happy you're chiming in also! Thanks for that. Turn the key on, dash light test, and no CEL. I wondered if I'd made that clear in my initial post. I had a lot of info to get out, and not enough battery time on my phone :laugh:.

[Mod edit: Moved reply from the quoted text]
 
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Tanka4ever

Tanka4ever

Member
Mooseman, thank you for the link in your reply. Shamelessly stolen from Gunny5:
"... IGN E (86) comes through the P/N switch. I was not getting power to 86. I jumped a wire from B+ to 86 with the relay in place and it started right up."
Didn't know that's where 86 was getting fed from, so if that's the case then the PNSS thinks it's in park, as it is actually in park. So I'm almost ready to rule out the safety switch.

I have some of the manuals, but I'm going to get them from your signature, and thank you for that invaluable resource you provide for us.

I'm going to go at the fuse block itself today. I myself own an 05 TB EXT with the 5.3, and I had an electrical gremlin with a microscopic hairline fracture in one of the copper trace wires between the layers of the fuse block. Caused CEL, reduced engine power, truck ran like crap. Threw codes for IGN switch and throttle body. So I'm going to at least check this fuse block for any issues and hopefully get acceptable resistances.
 

budwich

Well-Known Member
you will likely need to confirm that you have voltages and ground at the appropriate pins at the pcm connectors. NOTE: voltages tests are done on the voltage scale with reference to a KNOWN ground. Grounds are tested on the resistance scale with a reference to a KNOWN ground along with no powering in the system.

From there, you should check similar type tests (power / ground) at the BCM.

Further on your lights.... what is the history of the vehicle... ie. how did it get to its current state?
 
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Tanka4ever

Tanka4ever

Member
Fuse block out and sitting next to me. Have to drill out the bolts to access the copper traces. Will be doing soon.
With the positive cable only on the battery, can I do volt check from known PCM connectors that carry +12v and connect test lead to PCM connector to the ground of the battery and get continuity? As long as I have +12 from the source, that should make a complete circuit by grounding at the source also, correct?
The grounds will be the death of me. :Laugh: I checked the ones I see under the hood, cleaned them, dielectric greased them and retightened them. There was one that looked shady, and it was the main ground from the battery to the fender. Thinking of ground strapping it from battery to frame also just to get a better ground out of it.

Will report findings as I find them.

Thanks again!
 

Mooseman

Moderator
There's the grounds on the engine block on the driver side that are for main systems. This thread has all of them:
Electrical Ground locations
 

budwich

Well-Known Member
for voltage checks, you need to have the battery properly connected so that there are paths for the test... ie red lead on the test point, black lead on a KNOWN ground (most likely the negative battery post / cable). For resistance measurements, disconnect the 12v cable so that there is no power on the system. Set the meter on resistance and put the red lead on a test point and the black lead again on a KNOWN ground.... of course, prior to a resistance test, you need to know what your meter's "zero resistance" level is (ie. two test lead shorted together).... because when you are looking at small resistance in overall ground to ground connections in the system, you need to know the difference.

another question: does your instrument panel have a DIC display?

related to my previous point, there are 4 voltage "types" sent to the PCM, they all have to be there in RUN for the PCM to be "happy"... you need to check those pins at the pcm connectors... carefully not to damage the pin connectors... further look at the pins themselves to ensure none are contaminated at either the cable or the connector.
 
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Tanka4ever

Tanka4ever

Member
Sorry for the delay. Emergency call to work.
Fuse block entirely disassembled and reassembled. All copper traces registered 0.000 on my dmm. Checked every fuse for continuity and resistance. 0.000. going to start checking pcm wires next. Do I disconnect each of the 3 plugs one at a time with the key in run to test them? Ground the ground pin of my dmm to battery ground and test the plugs?
My cluster does not have the DIC. My 05 does, this 03 only has the mileage and trip and the bottom, and the PRND321 display.
I had the wire groups off the PCM this morning. There was no contamination, no corrosion, no sign of broken pins. The rubber gaskets for each plug was intact.
Will be away for about an hour. Have to replace the battery in my 05. Currently using the battery from the 03. 🤷
 

budwich

Well-Known Member
you can have all the plugs at the pcm disconnected. you are just turning the key to "ON" and testing for power at the 5 pin locations. pins 19,20,21 on C1 connector and 17 ,18 on C3.

BUT DON"T HAVE THE KEY IN "ON" when removing or setting the cable plugs... even better disconnect power when doing any cable moves.
 

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Tanka4ever

Tanka4ever

Member
Okay. C1 pins have voltage where they're supposed to.
C3 has power on 17, not 18.
Looking to see where the 12v reference goes now but hard on a phone
 

budwich

Well-Known Member
OK... the pin 18 was a test... :smile: its generated by the pcm not going into the pcm.

Not sure where that leaves you at this point, but potentially an in trouble pcm.... maybe.
The next place to check things is at the BCM which has some similar voltage requirements. You should also check the ground pin in the appropriate connector.

One other check, is related to the check engine light... pin 7 on C1 should have some sort of voltage with key on.

You have not indicated how the truck got to where it is.
 
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Tanka4ever

Tanka4ever

Member
I have no info on how the truck got to its inoperable state. My FIL bought it this way, and I'm usually good with wiring. This one is proving me wrong.

I will check C1-7 in a second. I got to playing around seeing what modules I can read with the Launch. Well, I got into the SRS system. Current code U1000, history codes...
B0100 electronic front end sensor 1 malfunction
B0103 electronic front end sensor 2 malfunction
U1000
U1041 loss of electronic brake control module (ebcm) communication
U1064 loss of dash integration module (dim) communication

I'll post in a minute about C1-7
 

Mooseman

Moderator
I wonder if there is something on the comm bus that's buggering communications. Before condemning the PCM, you might want to pull the comb in the main comm bus connector and then jump only the OBD connector to the PCM with a jumper wire and then check the codes. Try clearing them, turn the ignition off then on and check again. That connector/comb is under the driver side dash. It's black with a white top (comb).

Found this thread which is very similar to yours. In this case, it was damaged wiring at the PCM. Has a lot of the troubleshooting steps for the network.

 
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Tanka4ever

Tanka4ever

Member
Mooseman, I pulled that comb out yesterday and inspected it, found nothing wrong visible to the eye, and reconnected it. What wires am I jumping inside that to connect obd to PCM? I think one of the wires is purple, as I traced it to the obd port.
 

budwich

Well-Known Member
C1-7 reads 11.5v. battery voltage is 12.4v.
that's good... that basically means that the check engine light would light IF the PCM would send it a ground to set the indicator which it appears that it can't at this point even for the "bulb check sequence".

As you are "traveling" now, it appears to be a potential data / comms bus problem. I would also check the BCM connectors and voltages. Related to this, can you communicate with the BCM (its id is 064?)?
 

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Mooseman

Moderator
Here you go. SP306, which is the secondary splice pack, is located under the carpet under the right rear seat.
 

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Tanka4ever

Tanka4ever

Member
Bud, I will get your voltages in a few days. Wife brought me home for the night. :laugh: As of right now, I have work tomorrow, two Dr appointments, one of which is going to drain me, and Tuesday is a down day for me, basically if I need to nap, I get to nap. New medicine they say. Eyeroll.

Mooseman. So two splice packs. One dash and one under the passenger rear (middle) seat. On the latter, do I disconnect that comb while on the front pack jumping dark green and purple? I think I'm reading the schematic correct, PCM dark green and purple for obd. Please correct me if I'm wrong.

And thank you both for your wisdoms, and your patience. :smile:
 

Mooseman

Moderator
I wouldn't bother with the rear splice unless you determine something from there that's killing the comms. That's the only reason I included it.

And yes, correct for the wires.
 

christo829

Well-Known Member
One other quick question...this truck doesn't have any sort of aftermarket alarm/security system in it, does it? Just want to eliminate that possibility, and didn't see a mention earlier.

Good Luck!

Chris
 
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Tanka4ever

Tanka4ever

Member
Good morning gents. No update to provide yet, as it's raining out this morning and I'm doing this on the street.
Bud first. I misspoke about wire locations. I said those wires were on the rear pack under the carpet, but I know it's the main one at the dash. I think it's supposed to stop raining this afternoon. I will tie them together and attempt to read via OBD2.

Chris, I have the entire dash torn completely apart. The only aftermarket thing I see is an overhead DVD player and the wiring to make it play through the radio by means of intercepting the radio antenna on one frequency. I have completely disconnected it, thinking it might have had something to do with it. I see no evidence of any aftermarket remote start or alarm system.

Will report my findings as soon as I get them.
 
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Tanka4ever

Tanka4ever

Member
Update: no comm with PCM using the jumper wire between dark green and purple. No comm with PCM using the wire between light green and purple. Checked continuity of purple wire from the pack to the obd port, 0.000 resistance. So... Toasty PCM? New question arises, can I swap out the original pcm with one that is close to the specs of the current one, try the jumper, and try to read? Or does it have to be programmed first?
 

budwich

Well-Known Member
how good are you with "back probing" at the connectors without "injurying" them?
there are other voltges generated / switched at the PCM to somewhat indicate if there are internal issues. The example that I indicated earlier was one of those pins (12v reference).

You still have not look or posted anything about the BCM... that is kind of the main module for the vehicle. IF it isn't getting its stuff, it is not likely to allow other modules to do much.... although not being able to talk to the pcm is concerning... but could be a data bus issue with a babbler tying up things.

Others will tell you about another PCM... I think you can plug it in, it just may not run your vehicle but certainly you should be able to comms with it. Related the PCM, you checked your lighter fuse right? what lights are on your reader? battery at pin 16 on the connector?

correcting...

I "mispoke" about the DLC connection and now see it going thru the splice pack.

Disconnect your battery (no power on the system), take a resistance measurement at your DLC connector on pin 2 to a KNOWN ground. It should read something although with the multiples of the splice pack / bus configuration, it might not help / indicate anything with the result.

NOTE: your purple to drk green jumper should have been a direct connection to the PCM. IF you do the resistance test that I described with ONLY that jumpered / wired, that will tell you if the data path is terminated on something in the PCM.
 
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Tanka4ever

Tanka4ever

Member
New update. Tried to read with reader again, noticed I had no interior lights. Or radio. Power windows don't work. Power locks don't work. Power seat doesn't work. Trying to solve one problem and getting more. 😠 going to swap with similar PCM and BCM to see what I get.
 

budwich

Well-Known Member
chase that "rabbit", hope it ain't a "rat". Playing with splice packs can be a bad thing... :smile:
 

TJBaker57

Well-Known Member
What exactly do you have for a 'code reader'??

I would use a generic cheap Bluetooth adapter that allows you to speak directly to the network and/or simply eavesdrop on the traffic. This would allow one to see what modules are active and which are missing.
 
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Tanka4ever

Tanka4ever

Member
I tried an ELM327, didn't communicate. I tried an Innova Bluetooth module, didn't communicate. I've only got this far using a Launch CRP129X.
 
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Tanka4ever

Tanka4ever

Member
Bud, found the loss of body functions... Forgot to replace the 125A fuse when I reinstalled the fuse block. 🤦‍♂️ it's been a long few days.
 

budwich

Well-Known Member
no problem... glad you didn't get a "rat". I would suggest you do the resistance test on the dark green wire (pulled from the splice pack). That will measure back towards the PCM and in essence check how it is terminated.... leave the pcm connected but no battery power.
 

Mooseman

Moderator
And just so you know, with the splice pack's comb out, the modules won't be able to talk to each other so most things won't work.

If you do determine the PCM as being toast, you can swap in another one from a same year TB or Envoy with the same gearing (for speedo accuracy). All it needs is a security relearn.
 

TJBaker57

Well-Known Member
I tried an ELM327, didn't communicate. I tried an Innova Bluetooth module, didn't communicate. I've only got this far using a Launch CRP129X.

Sorry to keep hammering at this but didn't communicate how? With Torque App or another app?? If Torque...does it establish a protocol connection? Since the Launch device connects to ABS and another node that would indicate at least partial network functionality.
 

TJBaker57

Well-Known Member
Just noticed something...the Launch device has a battery of its own. Is there a chance that there is a problem with the vehicle data link port power or ground?? Maybe the launch is the only device that connects because maybe it doesn't require vehicle power???

Just spitballing here
 

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