I have an LS3/430, E38E PCM and 4L65e. It's in a 61 Chevy with custom PCM programming. Bench test on the PCM shows it pulling just over 5 amps. Scanner tool says "communication failure" so I cannot see codes or clear them.

I'll provide more details if necessary.

My question is, if battery dies and a high amp (200amps) jump start hooked to car to start it can that trash a PCM?

 

200AMP can fry ecm. I even burned up an EFI Live V2 on 200 amp by accident before.

 

Thanks. That's what I expected to hear.

 

Its not the 200 amp jumper/booster that kills the ECM, but the starter motor. When you key off the starter, this big heavy motor is still spinning and acts like a generator briefly putting out much more than 12 volts;its even reverse polarity! Normally a healthy battery absorbs this "DC motor inductive kickback" (Google it), but a very weak battery cannot. The proper way is to get enough charge into the primary battery so that it can absorb the inductive kickback from the starter motor.

 

That is very interesting. Thanks for the information.

 

Well, I got a backup PCM from a tuner here locally. He moved the OS/Build from my PCM to it. Took it to the car, and gave it a go. Didn't make any difference.

I think that the shop did something wrong with the wiring changes they were making.

 

Did your engine using the new PCM at least attempt to start? As in, fire up for 2-3 seconds and then die?

Rick

 

No. It does not attempt to start. At this point if we continue, I need to provide more details on the problem.

Reason for car in shop: Putting a cruise control on it that works like OEM units on an LS3. Needs to get gear information from the range sensor in the transmission (I've seen several different names for that sensor). When I wired up the unit, it would not work. So I hooked a USB cable to the unit, and to a laptop. Opened up a console and went into diags on the CC unit.

It showed when I turned it on, or off; showed if I pressed resume. But for Gear, it showed "no information".

So, to make a long story short, the thing that was attempted was to upgrade the 4L65E to the newer version. Turns out that even though I purchased it new in 2013 from Chevrolet dealer, it was the 2006 style of 4L65e. So they changed out the valve body, and sensors. I had to send the PCM and TCM to PSI Conversions to reprogram them with newer OS.

With those back, the shop needed to modify some wires at the TCM, and change the 15 pin plug at the transmission to a 17 pin plug, while changing some wire positions.

Early in this process the Optima battery went dead. Of course, when those get very low on charge, a normal charge will not charge them up. They put a hi amp unit on it to jump start it. I was in the driver seat. AT this point, before any wires were changed, it started fine. I did NOT look for an Engine light. Was happy it started. The Engine light in the Dakota Digital gauges is same color as all other lights in their digital gauge cluster, and so does not draw attention. You need to focus on the cluster. So the engine light might have been on, it may not have.

I put it on the lift, and they proceeded to change the wires at the trans connector. At this point the wires at the TCM had already been changed. After the connector wires were done, I started it up. Found no gear information still. And then I noticed the Engine light.

I had a code reader/canceller, and when I hooked it to it, it couldn't read codes. It said "No communication error". Backed it out, and they put their scanner on and saw same thing. They had another diag tool with about 16 different indicators on it (just lights). Hooked it to the ODBII port, and it indicated it had power, ground, Low pass, but no HI pass communications (I may be saying that wrong at this point. Going by memory).

He pulled the PCM and took it to the bench and put some probes on some pins and said it is drawing over 5 amps, which he never sees even if other things hooked to it. He felt the PCM was bad.

To further confuse things, we put the PCM back in the car, and at this point it won't even turn over. Checked with that 16 pin diag again, and now it shows both HI pass comm and Lo pass comm are down.

So at this point, took the PCM to a tuner up in Jax, and he had a backup one. He loaded the OS from my unit to his, and we tried that this afternoon. No go...same symptoms.

So, thinking wiring...but as I write this and think about it, it ran fine AFTER the TCM wires had been done (again, Engine light on...just didn't notice at first). So, if that ran before, it should still run after...one would think. The one thing that was happening was multiple jump starts.

I might mention further about the plug at the trans: he had some difficulties wiring it up initially, and I went into the office to do some research, and when I came back out, he had it wired. I told him to work on another car (they have lots there to work on), and I will double check the wiring, and it was correct. I checked slowly and diligently.

So, at this point, I'm sitting here thinking, what the heck? Wires at trans are rights; I assume the TCM wires are right because it ran long enough to get on the lift.

I may post all of this into a more appropriate thread at this point. I do know that at this point, the manager of the shop plans to come in and trace every wire involved in the changes to be sure they are correct.

 

If a tuner can read the OS from your non-working PCM, then it is not completely fried.
When you say "does not start", exactly what do you mean?
Does it crank?
Does it fire an occasional cylinder?
Have you tried spraying starting fluid past the throttle body? If it then fires briefly we know you have a fueling issue.
Have you tried putting a spark plug test light between one sparkplug and its wire?
Even with a ECM its not that hard to pinpoint whether you have fuel or ignition problems. We assume you have compression.

 

My comment of "it does not attempt to start" means no, it does not crank. It does nothing. No doing, no crack.

 

I was thinking the same thing. And of course since trying the second PCM with same results, I don't think there is anything wrong with it at all.
...
[QUOTE=mrvedit;20255448Even with a ECM its not that hard to pinpoint whether you have fuel or ignition problems. We assume you have compression.[/QUOTE]

Given that it's not even turning over, then of course those things aren't in play.

What is confusing to me is that it started fine AFTER the TCM wiring was changed, and initially after the wiring at the wiring plug at the transmission. Unfortunately, I don't know if the Engine light was on before changing the wires at that connector. So with that info, it's a bit harder to blame the wiring.

 

Obviously you have custom wiring, but on a much newer car, I would check if the starter trigger goes through a Park/Neutral safety switch. I'm pretty sure the ECM could be unplugged and the car would still crank.
Also, the ignition switch could have failed at a confusing time.

 

You probably have a blown fuse somewhere. The no crank at all has nothing to do with the ECM, and probably the reason you have no communication with it. Check the vehicle fuses and the fuses in you EFI fuse box....

T,

 

There is a neutral safety switch. I'll check the wires to that. It'd be a good place to see if power is coming to it when I turn the ign switch.

We did check unplugging the ECM to see if it would start. The wiring to that is one of the things that changed and is a possible issue. No change to symptoms.

I did check fuses, except, I did NOT check fuses in the engine harness. I'll do that.

Thanks everyone for the input. I really appreciate it. I'll post back what I find on the fuses.

It seems to me that the engine not starting is a separate issue than the Engine light and disability to read codes. Although the Engine light itself, I suppose, could be related to it not starting/no crank.

 

Good news...I found a wire off of the neutral safety switch.

So, now on to the other issues: why the comm is down on the PCM. They were changing some wires in the ECM to accommodate the new cruise, so I think it has to do with that.

 

Make sure you have power at the OBD2 connector. Unless they moved the wires off the comm bus, it should communicate. If it communicates on the bench, the wiring problem is in your car.

T,

 

The tech at the shop has some kind of device that tests up to 16 things. Just tests if active.

When we saw the problem he hooked that up, and found power good, ground good, low side comm good, high side comm down. He took the PCM to a bench and hooked up some jumpers and those to a meter. He said the PCM was drawing just over 5 amps, and nothing was hooked up to it. He said that is unusually high, and he suggested problems in the PCM.

As you know from earlier in this thread, I took that PCM to a tuner who copied the OS to a spare unit. Hooked that to the car and same symptoms.

Interestingly, the night he did the bench test, after reinstalling the PCM, the car wouldn't turn over to start, He hooked that test device to the ODBII again and then it showered both high and low comm down. As also noted above the start issue was because of the wire off of the neutral safety switch.

If anyone interested in the upgrade wiring instructions that we're used for to the transmission upgrade, I'll link them.

 

I was going to upload a shirt video showing the test box x but can't upload mp4s and no way to convert it on phone.

It's s CAN test box. It shows CAN low not working at this moment