1997 C5 electrical issue
Thread Starter
3rd Gear
Joined: Aug 2021
Posts: 3
Likes: 1
From: Roswell NM
1997 C5 electrical issue
Hey guys I’m new here my name is Kyle and I have a few issues I was hoping to maybe get some solutions.
Reduced engine power, serv traction control, no fuel, low coolant, engine temp maxed out. New pcm new bcm I put a new ignition in it and did the security bypass with a diode that reads the same as the resistors on the key. Did the relearn process 3 11 minute intervals of the ignition. Security light goes off when I turn the key to on position. Checked and cleaned all the grounds in the engine bay, checked all the fuses for 12v, the only dtc code that I can find relevant to these issues is u1225 serial data buss. The car turns over but won’t start. If I press the gas to the floor I can get it to sputter for 10 seconds then it dies. I’ve read countless forms on each issue and I’m coming up with nothing. The only thing I can think is that I used the old key with the new ignition which might cause this but I’m not sure that’s why I’m here. Looking for alittle help from you guys.
Reduced engine power, serv traction control, no fuel, low coolant, engine temp maxed out. New pcm new bcm I put a new ignition in it and did the security bypass with a diode that reads the same as the resistors on the key. Did the relearn process 3 11 minute intervals of the ignition. Security light goes off when I turn the key to on position. Checked and cleaned all the grounds in the engine bay, checked all the fuses for 12v, the only dtc code that I can find relevant to these issues is u1225 serial data buss. The car turns over but won’t start. If I press the gas to the floor I can get it to sputter for 10 seconds then it dies. I’ve read countless forms on each issue and I’m coming up with nothing. The only thing I can think is that I used the old key with the new ignition which might cause this but I’m not sure that’s why I’m here. Looking for alittle help from you guys.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,597
Likes: 4,057
From: Cape Coral, Florida
First, welcome to the Forum !!…With all those DIC warnings and the fuel gauge stuck on E (tank full) and water temp maxed out (engine cold) are your power windows inop ??….sounds like a serial data bus issue!!…you do have a communication code set…if you have a DVOM and know how to use it we may be able to help you…short video but instead of using a scope you can use a DVOM !!…BTW, a lot of these issues are caused by poor connections of the connector that is inside the rubber boot between the driver door and A pillar…just shake that boot a few times and see if she starts and runs…what happens is one of the modules (maybe the left door module in this case) loses power or ground and that power or grounds back feeds onto the serial data line…all hell breaks loose then !!
Last edited by C5 Diag; Aug 24, 2021 at 11:57 PM.
Thread Starter
3rd Gear
Joined: Aug 2021
Posts: 3
Likes: 1
From: Roswell NM
Yes the windows on both driver and passenger side roll up and down and locks work, head lights turn on and flip up, radio works. I don’t believe I checked the seat to see if it was working. I will check that tomorrow with my multi meter, I read a form saying you can remove the top of the star connector in the passenger floor and the car should start but when I did nothing happened the car kept doing the same thing.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,597
Likes: 4,057
From: Cape Coral, Florida
The first thing I should have asked is were the new PCM and BCM programmed by someone ??…these 2 modules are NOT just plug and play !!…I shouldn’t assume they were !!…don’t know if you removed both combs off the 2 splice packs but if you did the BCM and PCM will not communicate with each other so the car will not start !!…do you mean U1255 ??…no such DTC as 1225 !!…if you know how to “back probe” a connector you will have to see if you have 12 volts or ground on the serial data wire (purple wire) at either the DLC (where you attach a scan tool too) or at the splice packs. The issue has to be active at the time you are checking with the DVOM…we can check for a short to ground on the serial data line by using the ohm meter function of the DVOM.
Last edited by C5 Diag; Aug 25, 2021 at 08:33 AM.
Thread Starter
3rd Gear
Joined: Aug 2021
Posts: 3
Likes: 1
From: Roswell NM
Yes it is u1255 and the pcm was programmed by a tuner and bcm I bought was new so I don’t believe it was programmed, I’ll take it to the Chevy dealer and have it programmed, thank you for the advise!
