Working on a 04 envoy slt 4.2. 1 week ago it started hesitating when taking off and could feel a slight miss. This was when it warmed up, ran fine cold. Was driven 2 days like that then parked. Picked it up it was dead, charged battery started rate up. Sat for 1 day Now it won't start as in it does crank. I checked the starter relay and I'm not getting a ground out of the pcm. Tested neutral safety and thats working as well as the ignition switch. I also do not get a check engine light at all since it won't crank. The cluster also goes out in the start position. I'm thinking the pcm is bad but is there anything else I should check? It also won't communicate with my scanner and I check i do have power on pin 16. Any help would be great.
SOLVED! 04 envoy no crank
- Thread starter Mike 04 envoy
- Start date
Mooseman
Moderator
PCM failures are rare. Are you sure you tested the ignition switch properly? Check this out, which sounds similar to yours:
After that, we have these threads:
No Crank, Like Attempting To Start In Drive
No Start, Multiple U1000 codes, Class 2 Serial Communication Problem
So check for codes as well. Not all codes turn on the CEL, like U1000.
After that, we have these threads:
No Crank, Like Attempting To Start In Drive
No Start, Multiple U1000 codes, Class 2 Serial Communication Problem
So check for codes as well. Not all codes turn on the CEL, like U1000.
Thanks. I did test the ignition switch prior and all is working well there. I'm just not getting a starter ground signal at the pcm pin 48.
Mooseman
Moderator
There's a reason why the PCM is not happy and not sending the signal to the relay. Read the two threads I linked and go from there.
Thanks for the info. Went back and rechecked the powers out of the ing. Switch- all good. Retested starter relay input- power on 87,86. Put power to 30 and starter turns. No ground on 85 when ing in start.. Went to pin 48 at pcm no ground when ing in start. Checked and cleaned block and under hood grounds all looked good. Checked all fuses-good. I also get no check engine light on at all even with the key just in on position. I'm thinking the pcm is at fault but not sure if the pcm should be receiving a signal that its not? Any suggestions or further test you can suggest? Thanks for your help.
also want to point out if I jump the starter with the key on the envoy does not start, it just cranks.
Mooseman
Moderator
And you did say your scanner won't communicate with the PCM. Check the power inputs to it as well as grounds. You can find the schematics in the manuals in the link in my signature.
There is one ground point that is notorious for going bad is the one on the lower left side of the block. Check those out too.
There is one ground point that is notorious for going bad is the one on the lower left side of the block. Check those out too.
Thats correct. I have a basic scanner that can read live data and it won't connect. I just went out and rechecked the obd plug and power and grounds are there. Surprisingly all the grounds on the block looked good. I cleaned them anyway and with my power probe I probed the wires back aways and had a good ground signal.
Also want to note. I dont hear the fuel pump run with the key turned on and when I jumped the starter with the key on it just would crank and not start.
Mooseman
Moderator
Just to cover the basics, did you check all the fuses in the under-hood fuse box? Not just look but test with either a DMM or test light that both fuse posts carry power with the key on? try moving the fuses and relays as there have been instances of loose connectors inside the box. Lastly, pull the box itself and check the traces for any breaks. That too has been a regular occurrence lately as these trucks age.
I went across the tops with a test light I did not pull each one but ill try that . I believe this one came from the south as its not a rust bucket lol. Any chance I could get a link or a picture of what powers and grounds I should have at the pcm? This ones I've found on line I did check and they were there. Thanks for you help.
Suggest taking a few Static (Non-Jumper Assisted) Battery Voltage readings...Cold... and if possible, have the Battery Stress Tested at AutoZone looking for a Dead or Dying Cell.
These PCM-ECM use PWM (Pulse Width Modulation) to operate the Relays in the Under-Hood Fuse Box and are very sensitive to Sub-Optimal Power or Low Voltage Battery Conditions. Without a Baseline of 12.5 Volts DC... These systems can tend to misbehave.
It would NOT hurt to remove the Three PCM Connectors and Spray them out with CRC Electrical Solvent and once Bone Dry, then carefully re-attach them so that the Green Weather-Pack Silicone Grommets Do Not mis-align.
Also... Take a few minutes with your DMM to Test your DLC Port via Pins 16 for Battery + and Pins 4 and 5 for Grounds (individually) and if you don't see B+ Battery Voltage as a DBOM (Dead Balls On Match) between each other... then check over the Center areas of the (3) PCM Connectors for any breaks in the Ground Wires.
Just know that whatever the Mystery is that is happening right now, it will probably come down to being something either very simple.... or something obvious that all of us would likely overlook in your situation. Take a Step Back and look over everything you've done so far ...and see if anything jumps out at you.
These PCM-ECM use PWM (Pulse Width Modulation) to operate the Relays in the Under-Hood Fuse Box and are very sensitive to Sub-Optimal Power or Low Voltage Battery Conditions. Without a Baseline of 12.5 Volts DC... These systems can tend to misbehave.
It would NOT hurt to remove the Three PCM Connectors and Spray them out with CRC Electrical Solvent and once Bone Dry, then carefully re-attach them so that the Green Weather-Pack Silicone Grommets Do Not mis-align.
Also... Take a few minutes with your DMM to Test your DLC Port via Pins 16 for Battery + and Pins 4 and 5 for Grounds (individually) and if you don't see B+ Battery Voltage as a DBOM (Dead Balls On Match) between each other... then check over the Center areas of the (3) PCM Connectors for any breaks in the Ground Wires.
Just know that whatever the Mystery is that is happening right now, it will probably come down to being something either very simple.... or something obvious that all of us would likely overlook in your situation. Take a Step Back and look over everything you've done so far ...and see if anything jumps out at you.
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One other "Bugga-Boo" that I might get criticized for bringing up or Harping On Once TOO Often... is Rodent Infestations that have Plagued (pun intended) our GMT360s and GMT800s for the last few years, due to having so many parked and dormant SUVs sitting around unattended during the early part of the Covid-19 Crisis.
These small Mammals (Mostly The Common North American Deer Mouse) manage to climb the Tires and work there way through the under-hood areas, nest building around the harnessing and chewing on Wiring and Harness Connectors to wear down their endlessly growing incisors.
You should look for any signs of Dried, Desiccated Feces and Urine on, around on even inside of the Fuse Box. Look for signs of Dark, Greasy smearing on the Fuse Panel areas that will indicate their presence. Mouse and Rat Urine is "The Perfect Electrolyte" useful for stimulating Galvanic Corrosion.
BUT DO NOT TOUCH OR BREATHE IN THIS STUFF.
And Beware These Rodents carry the dreaded Hanta Virus that makes Covid-19 look like the Sniffles! During any Clean Up Activities Wear 11Mil Nitrile Gloves and an N-95 Mask as the airborne Viral Loaded Dust Particles can get inhaled and cause a pulmonary illness that Kills nearly 40% of those unfortunate enough to get infected. The lucky survivors can often take years just to recover from the debilitating effects of this horrible disease.
These small Mammals (Mostly The Common North American Deer Mouse) manage to climb the Tires and work there way through the under-hood areas, nest building around the harnessing and chewing on Wiring and Harness Connectors to wear down their endlessly growing incisors.
You should look for any signs of Dried, Desiccated Feces and Urine on, around on even inside of the Fuse Box. Look for signs of Dark, Greasy smearing on the Fuse Panel areas that will indicate their presence. Mouse and Rat Urine is "The Perfect Electrolyte" useful for stimulating Galvanic Corrosion.
BUT DO NOT TOUCH OR BREATHE IN THIS STUFF.
And Beware These Rodents carry the dreaded Hanta Virus that makes Covid-19 look like the Sniffles! During any Clean Up Activities Wear 11Mil Nitrile Gloves and an N-95 Mask as the airborne Viral Loaded Dust Particles can get inhaled and cause a pulmonary illness that Kills nearly 40% of those unfortunate enough to get infected. The lucky survivors can often take years just to recover from the debilitating effects of this horrible disease.
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I do have One Last "Electrical" Suggestion... Take a few minutes to Unscrew the Four (Five?) Galvanized Steel Posts that Hold the Fuse Block to the Under Harness Main Wire Bundle Connectors... and examine what is under there for any Chewed Wiring.
If all looks good and you have NO BROKEN COPPER WIRE TRACES OR SIGNS OF MELTED OR BURNED (Plastic) OR DAMAGED COPPER BENDS... then just Plug them all right back in and carefully Tighten them all back down without using Too Much HONK... :>)
If all looks good and you have NO BROKEN COPPER WIRE TRACES OR SIGNS OF MELTED OR BURNED (Plastic) OR DAMAGED COPPER BENDS... then just Plug them all right back in and carefully Tighten them all back down without using Too Much HONK... :>)
You need to then go to the pcm and check for voltage and grounds at the associate connectors CAREFULLY, without damaging the connector pins. Then you need to do the same at the BCM. The fact that you can't talk to the PCM does not bode well.
I was just remembering another strange incident where THIS Dude's Kid stuck a Penny inside of the Cigarette Lighter Socket ...and that was that... Dead Short ... and to the very same Fuse that services the... Wait for it ... The DLC... 8^O
PS ... A Shorted Cigarette Lighter will do EXACTLY the Same Thing...
PS ... A Shorted Cigarette Lighter will do EXACTLY the Same Thing...
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I like what @budwich suggested for checking the PCM Harness at the Three Connectors... So Visit Post #4 in THIS Link for access to ALL of the P-10 PCM PIN-OUT Diagrams for the GMT360s.
gmtnation.com
The one thing to be mindful of is to use either an LED Lighted Probe or a DMM instead of using any Incandescent Lighted Probe. You'll want to Beware of accidentally LOADING any PCM Circuit with 12 Volts DC that is only meant to handle 5 Volts DC. They generally Do NOT like that "Extra Current Surge" and thusly... the PCM can become "Bricked".
Checking for Electrical Continuity with the DMM should be enough to roust out the problem because any Broken Wires will reveal themselves right away. These Diagrams are Pretty, Damned Handy to SAVE nearby for use again...from time to time... :>)
BCM pinout
Looking to pick up on the reverse lamp circuit at the BCM. I've found sources that indicate it may be a light green wire, but there are several of them back there. One of which is a com wire that didn't take kindly to having a test light on it... anyone have a pinout for the connectors or a...
gmtnation.com
The one thing to be mindful of is to use either an LED Lighted Probe or a DMM instead of using any Incandescent Lighted Probe. You'll want to Beware of accidentally LOADING any PCM Circuit with 12 Volts DC that is only meant to handle 5 Volts DC. They generally Do NOT like that "Extra Current Surge" and thusly... the PCM can become "Bricked".
Checking for Electrical Continuity with the DMM should be enough to roust out the problem because any Broken Wires will reveal themselves right away. These Diagrams are Pretty, Damned Handy to SAVE nearby for use again...from time to time... :>)
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Thanks for the info. ill check that as well as taking the fuse box apart tomorrow. Hopfully something shows the problem.I like what @budwich suggested for checking the PCM Harness at the Three Connectors... So Visit Post #4 in THIS Link for access to ALL of the P-10 PCM PIN-OUT Diagrams for the GMT360s.
BCM pinout
Looking to pick up on the reverse lamp circuit at the BCM. I've found sources that indicate it may be a light green wire, but there are several of them back there. One of which is a com wire that didn't take kindly to having a test light on it... anyone have a pinout for the connectors or a...
The one thing to be mindful of is to use either an LED Lighted Probe or a DMM instead of using any Incandescent Lighted Probe. You'll want to Beware of accidentally LOADING any PCM Circuit with 12 Volts DC that is only meant to handle 5 Volts DC. They generally Do NOT like that "Extra Current Surge" and thusly... the PCM can become "Bricked".
Checking for Electrical Continuity with the DMM should be enough to roust out the problem because any Broken Wires will reveal themselves right away. These Diagrams are Pretty, Damned Handy to SAVE nearby for use again...from time to time... :>)
Thanks for everyones thoughts just wanted to post that it turn out to be a bad pcm. Replaced it and it started rate up and has been running fine.
Mooseman
Moderator