The car set for 4 months while I built the automatic transmission. Battery disconnected. Running fine before Tranny work. Installed rebuilt tranny and now the car will start and run intermittently. Started right up first time, ran for a few seconds, then died. All dash/electrical went black. Few secs dash came back on. Push green start switch, everything goes black. Open door with ign red light on, close door, horn beeps 3 times, hit green start button and it may/may not start and may run a minute or so, then dies and everything goes black. Dash comes back to life after a few seconds with green start switch. Hit switch, nothing. Pull the shifter back into reverse, green light comes on. Hit the switch, same thing. Going through all the processes, it may start at some point and run from a few seconds to a minute or so. It has even started on it's own a couple times. It will start sometimes without the green switch light on, but always dies. Installed new switch. Pulled the ECM and checked wiring connections. Pulled the Body Control Mod and have ordered the two relays on the back side of it. (always have foot on brake when trying to start.) First thought was loose ground in the tranny dept but seems ok. Second was switch,, New one. Next ECM and BCM. Not sure how to tell if it's them or not. New ECM?s are nearly $1000 and if it doesn't fix it, I'm out the bucks. Anyone else run into this issue.? Is there any where to send the ECM/BCM for testing? Also is there an ECM diagram whereas I can check to see if the ign, positive and ground are getting to the ECM? Thanks

 

No certain answer here, but I would replace the battery in the key fob. It's cheap enough to try.

 

Have you checked fuel pressure since sometimes it will stay running ??…just changing parts is not the right way to diagnose this as you may be building in problems for yourself with these parts…if you don’t have any electrical diagnostic experience it would be best to take the car to an electrical specialist…having a factory level or equivalent aftermarket scan tool will greatly help…have you checked the fuel pump ground which is on the outside of the left rear frame rail ??

 

The only part I've changed is a new push button starter switch. Been working on cars/Chevys since the late 50's. 1st Vette was a' 58 in 1964, after Nam a '63 then a '67 427, then 84 (junk). Presently have the 76 and 78. But this '05 has me stumped so far. I realize it's all computerized now, but, narrowing it down shouldn't be that hard. It is throwing a P0106 code. I've installed the OEM battery and changed the key fob battery. Fuel pressure doesn't fit the scenario because when it dies, all electrical components go black for about 10 seconds. Can't figure out why it ran perfect before setting 3 months.

I did read somewhere that if the ecm, is without power for an extended period of time, it will go to sleep and not wake up due to no power to keep the memory alive. This is why I wanted to find out if these things can be TESTED. So far I've not found a reliable source to have it checked?

 

A P0106 is a MAP DTC and yes the fuel injector “on time” will be altered which is not far off from fuel pressure and will make the car stumble and die…15 kPa is a little over 2 psi…to make sure your MAP sensor is not “skewed” the MAP/BARO with the Ignition ON should read 101kPa/ 29.9 inHg/ or 14.7 psi…if your scan tool can graph the MAP sensor reading I would do that while you ride around in the car…so the car dies for 10 seconds suddenly and then comes back to life ??…need a little more info…what is a “reliable source” that you are looking for ??…a shop ??…I know of an excellent diagnostic shop but they are 3 hours north of you outside Tulsa…BTW, the battery is what powers the ECM “keep alive” memory…all modules have an ignition feed or “wake up” signal and the KAM or keep alive memory…it’s a big difference between working on car for 50 years vs diagnosing them…2 different skill sets completely…also thinking maybe some intermittent communication issues…gotta test and not shotgun parts…are you using a “code reader” or a good scan tool that can read ALL modules ??

 

I fully realize working on cars/vettes 50 years and diagnosing these newer electronic vehicles is totally different,,,I'm not that stupid. And it's easy to say "take it to a qualified mechanic who has the tools that can find the problem and not "shotgun" parts". Well, there is such a thing of wanting to locate the problem myself just for the experience and knowledge, which is why I came here hoping someone might actually have a solution instead of berating me for trying to troubleshoot the problem myself.

Other than installing the battery that's called for, installing a new starter switch and buying two new relays that go on the back of the Bcm, I haven't spent that much money in my quest to figure this thing out.

​​​​​​​I've checked all my grounds, starter solenoid, battery connections, etc.

Latest update is that after replacing the relays on the back of the BCM (one being the starter relay) the car busted right off and ran for over a minute. It died and everything went black again. In a few seconds, the electrical reset and dash lights come back on. Hit the starter,,,,,everything goes black. So, I pull the NEW starter relay on the BCM and stick it back in, hit the ignition and it busts right off. Runs a few seconds and dies,,,everything goes black. Again, I pull the starter relay and reinsert it,,,,hit the ignition and it busts right off. Again, runs a few seconds, dies and everything goes black. EVERY TIME I pull the starter relay and reinsert it, the car starts, but after it dies in a few seconds, it will not start again and every time the ignition is pushed, everything goes black untill I re-insert the starter relay.

Again, all I did was pull and rebuild the tranny and install a new shifter cable. Again, the car sat for 3 months or so and the battery went dead. I don't feel like it's the ECM at this point.

Thank you C5 Diag so much for your information. I will check out all the information you contributed in your post. It's refreshing to get a solid lead for this problem. If it turns out to be as your post points to, then I've learned something. It's not about saving money by doing it myself, rather, for the knowledge obtained. Money is NOT an issue for me as far as getting a dealer to fix it. Again, I've been a mechanic, with diesel, automotive and aircraft most of my 78 yrs. I take it personal when I can't figure out a mechanical problem on an engine ( : .

And no one answered my question are the ECM's able to be bench tested and if so who?

 

To answer your question there are companies that bench test ECM’s like Flagship One (not recommended) and other companies but Google is your friend…I seriously doubt your ECM is bad…there are 2 relays…the RUN/CRANK Relay which you changed and the CRANK Relay…different inputs which will activate both of these…starting description below…I would go back and check all the connections you had disconnected during your transmission repair…when you say you “checked your grounds, battery connections” etc visually checking is not the best way…you have to test with either a DMM, test light or load light…let us know if you find a fix…there is no “silver bullet” here unfortunately…you never did say if you looked at that MAP sensor since a skewed MAP will cause the car not to run…if the car thinks it’s at 20,000 ft in altitude or 20,000 feet below sea level it’s not going to run right.