u0100

hello dir
my car cobalt read code u0100 what can i chenge for this problem
thanks

this fault code relates to a communication error (can bus). Lost Communication With ECM/PCM "A". what controller are you reading this fault from? are there any symptoms? is everything working ok?

can i chenge pcm

camn i chenge pcm

Lost communication with ECM/PCM. Check all grounds and connectors.

no problem when i Check all grounds and connectors

Ok. Yes you can change the PCM. There is most likely a strap securing it and 1 or 2 connectors that need to be disconnected.

bashar, have you gotten this working properly yet? Do you need more help with diagnostics?

have a 06 check cobalt had transmission problem wouldn't go foward so we pulled transmission sent it to a transmission shop to have rebulit, got transmission back started car and would go foward but, check engine light came on, pulled codes came back with codes u0100 u0101 u0140 u0121 all lost cummanatcation to all power control modules, and not really sure where to go from here can anyone help ???

you have a problem on the high speed lan,start by unplugging one module at a time until you get communication,the last one to be unplugged that communicates with the scan tool is the bad module.

thank you for your reply regarding your post on possible high speed lan, i guess am not familar with that if possible can you explain that please so i can try to direct my people on how to do this thank uou so much,

most GM vehicles from 2006 on have high and low speed lan,which is the rate of communication between modules,GM LAN communicates faster from one module to another,if you have a problem with one module it wont communicate with the rest of the modules or if there is a short to ground or short to power on the high speed LAN you will get no communication.I would start by unplugging each module one at a time until you have communication,start with the TCM,then the ECM,and so on,unplug the BCM last because its a gateway module and unpluging it first would disable all other modules.you also need a good scan tool to do this preferably a tech 2.here is a discription of high speed LAN,The data link connector (DLC) allows a scan tool to communicate with the high speed GMLAN serial data circuit. The serial data is transmitted on 2 twisted wires that allow speed up to 500 Kb/s. The twisted pair is terminated with two 120 ohms resistors, one is internal to the powertrain control module (PCM) or engine control module (ECM) depending on regular production option (RPO) and the other is internal to the electronic power steering module (EPS). The EPS is considered the DLC termination point of the link and the engine management controller is the other end of the link. The resistors are used to reduce noise on the High Speed GMLAN buss during normal vehicle operation. The high speed GMLAN is a differential bus. The high speed GMLAN serial data bus (+) and high speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level. The idle level, which is approximately 2.5 volts, is considered recessive transmitted data and is interpreted as a logic 1. Driving the lines to their extremes, adds one volt to the high speed GMLAN serial data bus (+) and subtracts one volt from the high speed GMLAN serial data bus (-) wire. This dominant state is interpreted as a logic 0. GMLAN network management supports selective start up and is based on virtual networks. A virtual network is a collection of signals started in response to a vehicle event. The starting of a virtual network signifies that a particular aspect of the vehicles functionality has been requested. A virtual network is supported by virtual devices, which represents a collection of signals owned by a single physical device. So, any physical device can have one or more virtual devices. The signal supervision is the process of determining whether an expected signal is being received or not. Failsofting is the ability to substitute a signal with a default value or a default algorithm, in the absence of a valid signal. Some messages are also interpreted as a heartbeat of a virtual device. If such a signal is lost, the application will set a no communication code against the respective virtual device. This code is mapped on the Tech 2 screen as a code against the physical device.

The car was hard to start,but when it did finally start it would stall out when put in gear. It finally started and my daughter got it home. I put the code reader on it and it says there is a link problem is this the OBC or is it a possible fuse somewhere?

ok well let me give you the 100 percent facts on what happen car was towed in, no foward, would go into reverse so we pulled trans had my sublet transmission rebulit it, got it back couple days later
installed trans connected battery check to make sure all wiring was installed check ground wire made sure was connected filled it with 8 qts of trans fluid went to crank it to check trans fluid level and no start just a click from starter so we were ok maybe battery lost charge from car being down few days charge battery, after awhile no start still so replace battery still did same thing, pulled starter now bench tested work fine, put it back in still no crank just ckick decided to order started install new starter same thing by this time started to check fuses and notice crank fuse was blown replaced with another one from fuse box blew that fuse got new fuse replaced them, still no crank just clicked called my rebuilter trany guy explain what was going on, told me to tow car to his shop so his guy can check i drop it off, get call couple hours later that starter cable from battery to starter was lying against fan assembly and that he connected and car starts to came pick it up and bring trans fluid to finish filling trans, so i get there they finshing filling trans with fluid and he take it for ride and say shifting rough and steering is hard and codes for u0100 u0121 u0140 u0101 come up and told me to leave and that he will check it out so next day i get a call from him that a needs a tcm so i go to local chevy dealership and pick it up take it to him and have him install it and still same problem well days gone by and he taken to some suppose gm speacilist and they are not able to figure it out, so on your best opoion base on the event of what happen can you lean on what problem came from and probaly is i told the trans guy to get car back so i can take it to dealership, i actullyed called them today and told service writer what was going on ask him to speak to his best tech and according o him they not sure either so they wanted me to take car tommarrow but maybe you can help so i called explain to them what issue they need to try to diagnosis thanks

Check your fuse first. If it's not your fuse, then the scanner may be defective.

I would check for a poor connection and terminal tension at the TCM connectors,I would also recheck all grounds,make sure none are loose or have a poor ground.I would also do a voltage drop on all grounds.recheck all the fuses also the fuse block inside the vehicle on the pass side console.(stupid question) when the TCM was installed was it programmed???also check for any pinched wires when the trans was installed.you might have another module bad,might not have been the TCM.I cant really help beyond this info,its to hard to diagnose this over the web,I would have to look at the car myself to see what happened.what ever fixes it post back with what you find.

as far as the hard starting goes.... did the check engine light come on on her way home ?
it sounds like a fuel pump issue, or maybe it was flooded.
How does it run now ?

wow i'am really thankful for your help, ends up when i purchase tcm from dealership i had ask parts guy if tcm had to be program and he told me no and after about a week of suffering with this car and seach web and listen to your advise i went to alldata to look into possiblly havin a bad bcm notice that tcm did have to be program once we did that fix problem, so i thank you so much, your the best !

I have checked the scanner with other vehicles and the scanner works.
I have checked all fuses and none are blown. I even replaced the CIG LGT fuse and BCM 3 fuse. I dont receive any voltage from pin 16. I also have an aftermarket radio which i may suspect to be the culprit. Any suggestions would be helpful.

Chances are the radio has caused the problem. The only thing you can do is follow pin 16 back to see if there is an open circuit.

check engine light is on.install scanner and im getting no communication error...checked fuses all ok. checked power and ground at DCL they are also OK. What next ?

The DLC has 2 ground circuts, make sure that they are ok.
Check the DLC with a test light and make sure that there is power (12 volts) there.

try the scanner in another car see if that is ok.

If they are ok then you may have an issue with the module that you are trying to communicate with.