The battery went dead in my 01 Z06 which was running perfectly and when I got it charged back up, the car spun over but would not crank and the display on the dash was reading "No Comm". By asking some people and reading some books I learned that the car has lost communication with the computer and will need to be reprogrammed. Can this be done any other way than taking it to the dealership or do I just have to eat the money and take it to them?

 

I don't know but here is a bump for you! I hope it gets resolved!

Let us know what happens so if anyone else has this problem it can be fixed or avoided!

Thanks,Matt

 

even a vette can have a batt. replaced without reprogramming. what made batt die? you say spun but didnt crank. did you test batt? did you do anything prior? make sure key is off. disconnect neg. term for 5 min. reconnect turn key on donot start for 1 min. turn off now try to start

 

I was doing some work under the hood and I left the door open long enough to kill the battery I guess. The only other thing I can think of is that I had the MAF unplugged the last time I cranked it to move it around the yard and I gave it a little too much throttle and it read that the MAF was unplugged and gave me a "Reduced Engine Power" display, which I have had happen to me before. Once the MAF was plugged back in and restarted on my other 01 C5, it cleared the display and operated normally so I wasn't thinking that had anything to do with it. I can put the key in the switch, turn it to the on position without starting it and the "No Comm" display immediately pops up. When I try to start the car it just spins over and over without firing up. It seems like it pumps fuel up to the engine because it fires and then shuts off immediately like it's just burning the fuel that was pressurized. I'm just exploring any options you guys might have before I go get abused at the dealership.

 

it starts it doesnt start. you were under hood [i'm not surprised] we have NO COM.

 

The car will NOT start. I had the airbox assembly off cleaning it and I started the car without the MAF plugged in. It's no big deal to idle the car around without the sensor plugged in but when I gave it a little too much throttle it showed me a reduced engine power display on the dash. After that is when I finished cleaning under the hood which in turn killed my battery (because the battery was bad). Once it was dead, it never started after that and the NO COMM come up on the dash display when I went into check the codes.

 

Can you get it to displat DTC codes ??? See C5 Tech tips on how to do this.

You say you were cleaning under the hood ... could you have gotten water or some other fluid in a connector? When you replaced the battery could you have hit any of the wiring to the PCM as it is located below the battery?

I'd look for a loose or shorted (water in it) connector. Especially if the Instrumentt Panel computer can't communicate with the PCM and cannot display DYC codes.

If it does dispaly codes, especially a P0602, then the PCM may need re-programming.

Good luck

 

Thanks for all the responses. Nothing so far has worked. I've done the manual re-learn by leaving the key on for 11 mins., off 30 seconds, for three consecutive times. Still no luck. I used no water or chemicals under the hood while cleaning so that eliminates this question. I did manage to collect the codes this time to maybe give someone any ideas of what to do next. Also, I noticed that my trunk release does not work on the dash or the keypad, which probably explains one or more codes. Again, this is a 2001 Z06, completely stock. These are the codes...

PCM No Comm.
TCS U1000 H C
BCM U1255 H
SDM U1000 H C
BO-RFA U1000 H C

 

You posted codes:

PCM No Comm.
TCS U1000 H C
BCM U1255 H
SDM U1000 H C
BO-RFA U1000 H C

The U in front shows that these are communication problems between the various computers (BCM, SDM, TCS, etc.) ... and the C means these are "Current" (right now) problems.

I am totally guessing here ... but I'd look at two possible issues ...

1) A ground wire has come loose. The computers (such as the PCM) can't get power because they can't get ground. Check under the hood in all the places you were working in and see if you might have knocked something loose.

2) somewhere in the wiring harness wires have gotten exposed and are grounding when they should not. Again look around where you were working and see if possibly there are exposed (bare) wires.

Beyond that, I'm outta ideas ... maybe someone else has other ideas ??

Good luck,

 

My guess is that somehow your PCM has been corrupted and will at the very minimum need to be re-flashed by the dealership. You may have to have your car towed in and they can connect to it and attempt to restore the operating system to your PCM. If that does not work you will need a new PCM.

 

The "No Comm" message is very odd to get at the time you are getting it. When you turn the key on without cranking exactly what does the IPC do? Does all the gauges sweep up and back? Does the DIC display the standard "CORVETTE BY CHEVROLET" before it displays the "No Comm" message? Does pressing the DIC buttons change the DIC display?

Exactly what did you do when the battery was dead? Did you jump start the car or charge the battery with a charger? I'm betting that somewhere in that process electrical system was hit with reverse polarity, either with jumper cables hooked up backwards or a charger hooked up backwards.

I appears you may have a serious problem with the PCM and possibly the IPC. Nothing on a C5 should need reprogramming just because the battery went dead. They may forget their learned fuel settings and my not run the best for the first little bit until they relearn the mixtures and stuff but nothing should keep the car from starting.

 

The NO COMM message means that the IPC computer can't talk with the PCM. The PCM may in fact be OK, they just aren't talking. If the problem was a PCM failure you'd get a P0601 and/or a P0602 and/or other codes. It definately sounds like a wiring issue ... either the PCM is getting no power, or, given the fact the IPC is showing comm failures with other computers like the BCM (DTC Uxxxx codes) there is a problem with the data bus.

Check FUSES .... on my car Fuse #16 and #23 in the engine compartment fuse block controls power to the PCM ... check your Owner's Manual and see if a fuse has blown ... maybe it is as simple as that ?? Let's hope so ...

 

I believe that is not correct. If I'm reading the post correctly he is getting the "No Comm" message right when he turns the key on. That was why I was asking exactly what did the IPC do when the key was turned on. When the IPC is powered up it is programmed to sweep all the gauges and display "CORVETTE BY CHEVROLET" message. The IPC will do this if it is in the car or powered up out of the car. Even if powered out of the car the IPC will do the above then display "REDUCED ENGINE POWER", it will not display a "No Comm" message. So if I read the post correctly he is getting the "No Comm" message at a odd time. Different firmware in the IPC may display different things, but I'm speaking from experience with a 2001 Z06 IPC. Hopefully he will verify exactly what he is seeing soon. I agree that when checking codes the "10 PCM NO COMM" means the IPC can't talk to the PCM on the class 2 serial data buss, that is correct. Which in this case does not seem to be a wiring issue because the IPC has class 2 communications with other modules so the IPC is properly connected to the class 2 star buss connector which means if it was a wiring issue it would have to be between the PCM and star buss connector with is only about 2 foot run on these cars, not likely a problem in this case. The received codes U1000 and U1255 both mean that the modules displaying those either of those two codes, has not received at least 1 needed critical operating parameter over the class 2 serial data buss within the last 5 seconds. I take all these U codes as each of those modules is saying "I have not received the data I need from the PCM in the last 5 seconds". If you notice, most all U codes are current, meaning it is an on going communications problem, and we know there is a on going communications problem with the PCM since the IPC can not communicate with the PCM to retrieve stored codes over the class 2 serial data buss. Therefore I'm leaning towards a PCM problem, not a wiring problem.

Near the end of post #4 he states the engine does fire for just a second, which sounds like it is firing on the enrichment fuel the PCM will spray pre start. So it sounds like the PCM is working somewhat, enough to drive the ignition and pre enrich the engine, but is sounds like it may have logical problems which is keeping it from running the engine.

Since all this started right after a dead battery, it is likely the electrical system was hit with reverse polarity by either jumper cables or battery charger.

The fuse idea is very good. I would check every fuse in both fuse boxes.

 

The PCM may have already set a P0601 and/or P0602, or any other code. But now we can't talk to the PCM, so at this point we have no idea what codes the PCM has or has not stored. So until the PCM will talk to us again we have to use other clues to figure out what is causing the problem.

 

one more thing, is the "security" light flashing or is it on steady when the key is turned on?

 

I am getting almost the same codes with my issue

U1016
U1255
U1000
B2482
B2723
C1233


I get the Reduced Engine Power after the Corvette Display

And my PCM says NO COMM
I also get a SERVICE ENGINE SOON light and the Check Engine Light keeps clicking, along with the Fuel Pump Relay and I can hear the same type of clicking in both fuel pumps.

 

mi97vette,

You posted the following codes:

U1016 - Communication (Comm) problem with PCM
U1255 - Comm problem - missing parameter or sending module ID
U1000 - same as U1255
B2482 - Problem with back-up light circuit
B2723 - PASS-Key resistance incorrect (wrong key or bad key)
C1233 - RF Wheel Speed Circuit Open or Shorted

These codes will have either an H or a C after them ... H are History codes and the problem does not exist right now ... C are Current codes.

If the B2723 is Current, the key you are using to try and start the car has the wrong resistance accross the pellet compared to the resistance the correct pellet has.

If you have a spare key, try using that, especially if the B2723 is a Current code. At least 3 minutes must elapse after you inserted the bad key, ignition OFF (no key in it) before you try the other key (the delay is to make it painfully slow for a thief to try combinations of keys with different pellets in them).

If all the above are H codes (the Uxxx codes will undoubtedly be C's), I'd clear them from the system, and like I and SpeedyZ are recommending, check all fuses.

 

The codes I have listed are all current (c) codes did not want to list all the history codes.

I only have one key, would a bad key do all of this?

 

depends on what you mean by "all of this" .... For example the B2482 (back up lights) would have nothing to do with a bad key.

But, (and hopefully someone more knowledgeable than me will step in here .... LOL) a bad key will definately disable the car. I don't know if the NO COMM with the PCM is because of the bad key, or another issue, but if you clear the codes and are still getting a B2723 when trying to start it, then the key is definately an issue.

I don't know how familiar you are with PASS-Key .. so skip this if you already understand it ...

Look at your key. There is a black "pellet" imbedded in the metal part of the key. It has a contact area (little metal strips) on each side of it. When you insert the key and try to turn the key to the START position, two things happen:

1) The cuts in the metal key have to match the lock itself. Just like your front door key to your home, this is a "mechanical" way of insuring that the key matches the lock.

2) The BCM runs an electric current through the pellet ... the pellet is basically just a resistor. If the resistance level matches what the BCM expects, then the car will start. If the resistance level is incorrect, the car will not only not start, but the BCM will now "lock out" any more attempts to start for 3 minutes. The BCM is "smart" enough that while it is running the 3 minute timer, and you disconnect the battery hoping to reset the timer ... well it won't, the BCM will pick up the 3 minute clock once power is returned.

You might try taking something like a pencil eraser and "cleaning" the pellet contacts on both sides of the key. Possibly some dirt or other "gunk" is causing the resistance to be far enough out of range that the BCM doesn't recognize the key as valid.

If you've cleaned the pellet contacts, checked all the fuses, and looked over your wiring (you never mentioned if you'd done any work on the car prior to this problem ... check carefully around anywhere you worked for a loose ground cable or exposed/shorted wires) ... then I'm outta ideas ..... Anyone else wanna jump in here ???

 

Ok. When the ignition is off, security light flashes. Ignition on, no security light and gauges do sweep. This is the exact sequence...ignition on, corvette by chevrolet, service vehicle soon, reduced engine power, service traction system, service active handling. Also, to clarify what I meant, the ipc display doesn't immediately show No Comm. Only until I read codes does it give me that display. To my knowledge, noone including myself ever hooked cables or a start/charge device to the battery while in the car either correctly or reverse polarity. I desperately hope this gives some of you more info to help me. Also, worst case, where's the best place to get a pcm? One more question...do I need a specific pcm because we have other C5's here that are damaged that I could "borrow" from one of them but I'm sure model years have to be comparable.