LSGUN

Ok so this past labor day I drive my vette about 3 hours away to visit my friend in the military and the car ran great no issues what so ever, and when I go to leave the car cranks but would not start after doing some research and troubleshooting we narrowed it down to a faulty TAC module and PCM that I have just recently replaced and after some fiddling around we managed to get the car started but the car wouldn't idle because the used 98 pcm I bought for it had a pretty radical tune on it for a big cam my engine is stock so I thought no problem I registered the PCM onto my friends HP tuners and downloaded a factory 98 ls1 pcm tune for some reason it took 4 credits (2 for the PCM registration) and (2 for the factory tune software ) so here I am 200 dollars worth of tuning a 250 dollar TAC module and 115 dollars worth of secondhand PCM later and I have a nice long list of problems that make me a happy corvette owner once again

Here are the codes I pulled off of the car

PCM No Communication (was communicating before we tried to tune it)

Traction Control Codes
- C1241 HC Magna steer Circuit Malfunction
- C1276 HC Delivered Torque Signal CKT Malfunction
- U1255 HC Generic Loss of Communication

Body Control Module Codes
- U1255 HC Serial Data Line Malfunction

SDM No Communication

Radio Codes
- U1064 H Loss of Communication with BCM
- U1096 H Loss of Communication with IPC
- U1016 H Loss of Communication with PCM

HVAC Codes
- U1064 H Loss of Communication with BCM
- U1096 H Loss of Communication with IPC
- U1160 H Loss of Communication with LDCM
- U1255 H Serial Data Line Malfunction
- B0333 HC Outside Air Temp Sensor Open
- B0361 H Left Actuator Feedback Short to Ground
- B0363 HC Left Actuator Feedback Open
- B0441 HC Left Actuator Out of Range

SCM Codes
- U1255 H Serial Data Line Malfunction
- U1064 H Loss of Communication with BCM
- U1016 H Loss of Communication with PCM

RFA Codes
- U1096 H Loss of Communication with IPC
- U1064 H Loss of Communication with BCM
- U1000 HC Loss of Communication Undetermined

Bill Curlee

Well,, the 97 and 98 PCM dont need any credits to tune. I think your troubleshooting went haywire.

All those NO COMM and U series DTCs tell a story. SOMETHING is wrong with your serial data buss.

Look to the LEFT of the BCM and find the two thin STAR Serial data connectors. Find the one with FOUR wires and pip the top odd of it.

Clear ALL the DTCs and see if you have comms back.

You can pop the top off the other STAR connector and jumper the PCM and BCM together and the engine should run with proper comms between the BCM & PCM is necessary. You dont need the other serial data line to get home in an emergency.

Get the serial data issue resolved. Something is shorted or corrupted on that line causing the rest to fail communicating.

Of all the modules listed, I suspect the seat control module before all the others.

Bill

Bill

LSGUN

Thank you so much for the advice Bill I will check into that tomorrow and let you know what I find out

LSGUN

So I topped off my cars battery over the night and the charger stated that the battery was fully charged this morning, put the battery in the car and volt meter on the cluster was only reading 11 volts tomorrow I will remove the battery and have it tested because my friend told me that low voltage can cause really weird electrical problems like the ones I am having. I also disconnected the STAR serial data connectors beside the BCM and got a lot more No Comm codes like Bill explained but no start however I mistakenly pulled both STAR connectors Tomorrow after I have the battery tested I will pull only the one STAR connector with the 4 wires like Bill told me lol and see where that takes me

LSGUN

Ok so I topped off my battery and load tested it and it was a bad battery autozone replaced it free of charge under warranty so the good news is that I now have a fresh battery and I was hoping that it would get me a little closer to solving my electrical woes so I put the new batt in my car topped off and still no communication with the PCM why couldn't this happen in the summer its 20 degrees out and I have no garage lol also I would like to point out that this brand new battery fully topped off 100 percent still had my volt gauge reading 11.7 volts is that normal? its been so long since my car worked I forgot haha

Bill Curlee

100% Get that fixed first. If it were me, I would measure the voltage on all the PCM and BCM fuses to make sure that there getting FULL voltage when the ignition switch is in RUN.

If the ignition switch isnt providing full voltage, the PCM may not be functioning properly.

Bill

LSGUN

Thank you 8vette7 and Bill I will look into that this week and see what I can find out Also for what its worth I did check every single mini and maxi fuse in both fuse compartments over the weekend and the only one blown was the mini fuse for the horn lol. and Bill if its not too much trouble do you have any pictures of the STAR serial data buss connectors you could show me just so I am sure that I was unhooking the correct ones I think I found them I just want to be sure

dadaroo

Here is what the 2 look like:




Here the schematic for each. Pulling the cap off the 4 wire one will take the door and seat module out of the circuit.

LSGUN

sweet thanks yeah those are the connectors I pulled off I will try the 4 wire one tonight or tomorrow and let you know what I find out

LSGUN

Ok so its been a while since I last updated this thread but I sourced every chassis ground on my C5 yesterday and cleaned up each contact point and pin. One of the ground boxes thats near the coolant overflow tank was badly corroded so I cleaned it up like new and pulled up my codes as follows (I have the climate control unit and the radio pulled out of the car right now so I understandingly got no comm codes for those two)
PCM no comm.
TCS C1241 C Magna steer Circuit Malfunction
C1276 C Delivered Torque Signal CKT Malfunction
U1255 C Generic Loss of Comm.
BCM U1255 HC Serial Data Line Malfunction
SDM no comm.
RFA U1000 HC Loss of Communication Undetermined

I pulled the 4 wire serial data link connector out and tried it but still no good and heres something odd and I wasn't going to post this thread update until I had the batt fully charged because I might be wasting my time lol but I measured the volts on the battery when it was out of the car and not plugged in and it read 11.6 volts but when I hooked the battery up to the car and read it it only read 8.7 volts that I just don't understand so im guessing my car is drawing a lot of unnecessary electricity

Bill Curlee

Do your self a favor and take the fully charged battery and have it properly load tested. I'm afraid that it sounds like your battery is toast.

Nothing in the car is going to draw a good properly functioning battery down to that voltage except the starter cranking over the engine. With a good battery that will only drop it down to about 10.5 - 11 VDC on a cold start.



Bill

dadaroo

FYI

If the battery is

12.5 = 85% charged
12.4 = 65%
12.3 = 50%
12.2 = 35%
12.1 = drained

LSGUN

Just got home with the battery tested good and is fully charged still no comm. basically the same as yesterday :/ same codes as yesterday but now the left and right door control modules are not comm. either

Bill Curlee

For a module to register NO COMM, it:

- Has a damaged seral data wire
- Has insufficient or no power
- Has a poor or no ground
- The module has power & ground and is electrically bad inside

When you have MULTIPLE No Comms:

- Something on the serial data buss is shorted or causing noise so the modules can not communite
- The BCM is having issues and not able to communicate with all modules.

I know ive said it too many times but, make sure that your HOT in RUN & START powered fuses (supplied by the Ignition Switch) for the BCM are all at full battery voltage.

Bill

Bill

LSGUN

Will do thanks again for bearing with me guys ill check it out hopefully this weekend

dadaroo

I just helped a guy with PCM No Comm. It was a bad ground G106 on the right side of the engine block.

Everything else checked out OK from Bill's post above so he looked at the ground and problem fixed.

LSGUN

sorry its been a while since I have been able to mess with the vette im never giving up lol ill be sure to keep you all posted just wanted to let you all know im still alive lol I will definitely check the engine ground might have missed it before I did clean up a lot of grounds that had corrosion on them though they did not fix the problem it was still some good preventative maintenance.

LSGUN

Just got some time to work on the vette again and I do have one question regarding the seat and door control modules. My seats function as they should and so do my door locks and windows so would this rule out the possibility that a seat or door control module is corrupting the serial data bus communications with the BCM? Also when I turn the key to the on position the BCM makes a click noise for what ever thats worth to the investigation lol also would a bad PCM corrupt the serial data line just as a door control or seat control module would? Im going to go over voltage at various points in the system tomorrow and see if i can get myself back in the groove and start eliminating possible causes ill keep you all posted.

runner140*

Your baby has been sick for over 16 months? These are fun cars and shouldn't be in bed that long. Suggest you contact someone in your local Vette club in Maryland who can give you some hand on help.

LSGUN

Actually the car has been broken since September 1st 2014 😞 So I'd say it's been sick for about 26 months. My friend Shayne has a c5 and he's going to come over this weekend to help me work on it so I'm going to make a list and start narrowing things down again it's been so long since I had a chance to mess with it that I need to refresh myself starting with grounds I noticed last night that the ground strap on the engine looked a little corroded I do think it's strange though that my door controls and seat controls function perfectly but I have no communication codes for them and like I said I took the 4 wire star connector to the serial data line off and still had the same symptoms so should I rule out the seat and door control modules?