Dead vehicle after Clear DTC w/ V2

[FeetDry]

The 12200411 (LS1B) PCM was working fine. I'm chasing some DTC's. I plugged the V2 into the ODB2 port then used the V2 keypad to Diagnostics->Trouble Codes->Clear DTCs. The V2 was also plugged into the laptop, but the laptop was in sleep-mode. It took a longer-than-typical crank time to get it started. It would stumble when driven. After 20 seconds, it started to backfire under part throttle. I shut it down. Now it won't start. Clearing the DTC's has hosed the PCM.

I flashed a couple known good cals. It won't start. I did a complete (cal+OS, save CASE data) reflash from a couple known good tunes. It won't start. It is firing against the starter. I reflashed the complete cal+OS with clearing the CASE. It won't start. I have unburned fumes out the tailpipe. I have a couple cyls firing against the starter.

1) What did I do wrong?
I typically use a cheapie Actron to clear the DTC, emission, FF data.
I don't typically use the V2 to clear the DTCs.
I don't typically use the V2 keypad todo anything. (I use the V7.5 scan & tune app.)

2) Any suggestion as to why I can't bring the engine back to life?
I doubt something is broken. I pretty sure this is a PCM issue. (Why won't the reflash fix it?)

V2 info: BldrVer: 2.07.06 FirmVer: 2.07.52

[joecar]

What was laptop being powered by...?

What DTC's had you seen...?

[FeetDry]

Currently there are no DTCs.
I was chasing a random P300 (misfire). Which looks like cyl #1. (I don't think this is related to the no-start issue.)
The laptop was on battery power.

I took a look under the cap & rotor. Checked the fuses. Everything looks OK.
After rechecking the DTCs I tried to start it. It started right up. The problem has gone away.

I'm not sure of the cause.

[joecar]

Hmmm, now I'm very curious...

[Blacky]

That type of behavior may be caused when a reflash is finished and the countdown period is not allowed to complete. The reason for that is the PCM's RAM that is normally used to hold various run-time data is re-purposed by EFILive's boot loader program that reads or flashes the controller. If the engine is started without allowing the timer to complete then the RAM may not get reset back to its correct run-time state. That means most of the run-time data in the PCM will be random/corrupt data which could cause all manner of weird problems.

I'm not sure why that would start happening after a clear DTC operation. However, a clear DTC operation may cause the learned values like fuel trims and air flow to be reset. That may have been enough to trigger the initial "engine running badly" situation. A subsequent re-flash (or even just a read) without allowing the countdown to finish completely could have exacerbated the problem.

But I'm just guessing, I can't say that is the problem for sure. It may just be an intermittent fault in some other part or system.

Regards
Paul

[FeetDry]

I understand that failing to wait 15sec "sleep" period can mess things up. But in this case, I waited for the full 15sec timer to expire every time I flashed the cal and the OS+cal.

I originally posted because I thought I did something wrong. Something like, the PCM is hardware A and the V2 was set for hardware B. So the clear DTC operation cleared the wrong mem-space, which hosed the cal or OS. This guess doesn't explain why the cal & OS reflash didn't fix the issue.

I'm thinking the clear DTC operation should be an hardware/platform independent operation/command. So this guess is probably wrong.

[joecar]

Looks like the PCM got into a "strange state" and then reset itself...

clearing the DTC's won't clear the wrong mem-space (or any mem-space)... it is a command that the PCM interprets...

so I'm still curious if you can repeat it.