Hello and thanks for your help! 2002 Z06...Recently purchased, so I'm not real familiar with the car, but I went to crank the other day and got...reduced engine power, low fuel, etc. Checked codes and first was No communication with PCM! Cranks but will not fire. Only thing I have found AND it did not help is I had left G302 ground rear passenger door post off (reconnected but did not help). I've searched post and tested grounds, fuses, disconnected pcm and bcm, waited 30 minutes and reconnected, changed pcm...still no communication, did a rain dance...thought it might help!
EFILIVE scan will not connect. Gas gauge reads empty and temp is maxed out when key is turned on. Security light is always flashing, until key inserted and turned on...is this normal? I think there is a column lock bypass installed, but not sure of make.
Any ideas? Would be greatly appreciated!
Thanks, Jimmy

 

The last identical issue I worked on the PCM ground was loose. If I remember it is G106 on the right side of the engine and a little hard to see. Could also be the connector there needs to be cleaned. May have to pull the battery to get to it.

Could also be it is not getting power. Not at home to tell you what fuses to check but use your owners manual in the interim and I will validate which ones they are.

Pretty sure if you only have No Comm on the PCM it is power or ground unless the PCM went south on you.

Security light indications seem normal to me.

Let me know what you find out.

 

Found this on my laptop.

PCM +12V power feeds from underhood fuse box (engine fuse box)
Fuse #23
Fuse #16
G106

 

Thank you dadaroo! Both fuses are good and 12 volts to them with key on. Trying to get to G106...that thing is hidden! Cleaned battery ground below box, as well. I will check for 5 volts at computer when I hook battery back.
Jimmy

 

With all those digital issues, you most likely have a corrupted serial data buss. My 02 Z does the exact same thing when my serial data buss gets corrupted.

There are TWO thin connectors to the LEFT of the BCM... Find the one with FOUR wires and pop the top off of the connector and see if the car will start and run. You will loose COMMS with the SCM, LDCM & RDCM but everything else should be back to normal.

If that doesn't help, see if the BCM is or was wetted. Feel under the carpet... BCMs HATE water!!!

Bill

 

Thank you Bill. I had tried the serial buss from one of your post helping someone else with similar issues. I will try again, though! I had thought it might be water issues, but no indications. Drains all seem to be open, although I could have missed one. I did miss the two grounds at each side of radiator...cleaning them now, but honestly they look good. No obvious corrosion. I have disconnected the bcm again and will check...might open if nothing else looks wrong.
Jimmy

 

Something is cause a serial buss issue.. Im SURE about that. If you have corrosion inside the BCM from a past wetting,, could cause an issue.





Be careful The BCM is ESD Sensitive and if you static ZAP it,, its as good as DEAD!


Bill

 

Gentleman...I have checked the 2 fuses and cleaned the G106, absolutely no water damage in bcm, disconnected serial data buss...nothing! Still all the codes and no communication with pcm! Other ideas please?
Thanks, Jimmy

 

Time to break out the OHM Meter and check the serial data lines to make sure each module has continuity to the STAR CONNECTOR.

Here is the serial data buss schematic:



Have you looked under the battery and insured that you have NOT had a battery acid leak on the PCM wires? It happens.

Bill

 

Thanks for schematic...I had looked through manual quickly for it but missed it. I'll check in the morning!
Battery is fine, no acid leak. Even tried another battery today. I am baffled! I'm not great with electronics...but generally can chase down the issue. But, this thing is crazy! I even checked ignition switch, just to be sure.
The one thing that baffled me...when I checked the PCM pins from switch when "ON", I think one was pin #19 in C1...it was reading 24 volts! Maybe I boobed, but the 2 pins that were always "HOT" read 12.6 or so...battery voltage. Think there is anything to that?
Truely grateful for the help!!!
Jimmy

 

Nothing in the electrial system can read 24 VDC Maybe it was 2.4 or .24 but,,,, NOT 24

Better read those pins again. 12.4 is fine.

 

Well...I didn't think there was any chance of locating my electrical gremlin by myself, so I ask my son to come help after work. He is blessed with gobs of common sense! Well, after over an hour, he was ready to pull his hair out! We checked grounds, continutity, key on, key off, etc. What was throwing us was we were getting 12 vdc at underhood fuse box with key "ON" @ pin 16, with fuse pulled, but put fuse back in and it went away! Same for several other fuses powered with key on. So, he pulled switch and we started testing again. Continutity checked fine on large pink power wire, but voltage dropped when fuses was in place. After 10 minutes or so of fiddling with ignition switch...there was 12 vdc with fuse in! We hurriedly put wires and components back in place and it fired right up!!! Our initial thoughts were, the switch must be suspect...after several cycles on/off we were content the switch lay at the root of the problem. Then...I go to put windows up and call it an evening...NOTHING! Drivers door window switch would not power the windows. I figured I'd left the serial buss bar unconnected, but not...it was together. Then my son tried the passenger window switch and up it went. Great! I go to grabbing at the boot between frame and door and sure enough windows start working! Wiggle it...they stop...wiggle, they start! I had checked this before!!! It was one of the first things I'd looked at because of a post by Bill Curlee on a similar situation. So now I'm really baffled! I'll pull door connecter out today and see what it looks like...BUT, is it the issue or the ignition switch or some other gremlin I still have not located! Time will tell...

 

Lurking

 

LOL! The only way to be POSITIVE that you have a good connection between the MALE and FEMALE pins in any connector is to get a spare male pin (same size and thickness as the male pin in the plug) and see if there is physical resistance when inserting and removing the male pin into and out of the female pin.

If there is little or NO insertion/retraction resistance, the female pin is too loose (spread apart) and needs to be fixed or replaced..

BC

 

The same test needs to be done to the two connectors that connect to the ignition switch.



BC

 

I just love it when BIll talks dirty...