No crank no start no tail lights power steering message - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 4 (permalink) Old 03-04-2018, 06:27 AM Thread Starter
Join Date: Mar 2018
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No crank no start no tail lights power steering message

After much studying on the internet and reading hundreds of posts and watching dozens of videos and reading pages of wiring diagrams... my sons 2006 Chevy cobalt ss 2.4 liter is finally fixed. I have read pages of people saying everything for these issues is everything from adding a wire to the tcm case to a dirty fuse to burnt modules... guess what? It can be any of them or all of them. I would like to tell you what I found and how I found it.
My son called me one day to say his car wonít shift and had the power steering message. I towed the car to my garage and got started. First thing I did was check for codes and found the p2105 no communication with tcm. It also had a u 0001 no communication with power steering. I began by testing pins in the dlc and had all good powers and grounds. Next I disconnected the battery and ohm tested pins 6 and 14... there should be 60 ohm. If you find 120 you have a broken wire or a burnt module. I found 120. I googled a video of a guy testing an hhr data circuit and it was a good guide for the cobalt. I tested at each module for the ohms and was able to get 64 ohms by bypassing the ebcm. After going to a junk yard I was able to install a used brake module and the data ohms came down to 64.. remember I said we need 60 though so i was back looking for a poor connection. The car still wouldnít start unless I shut the head lights off. I found a remote start had been installed after market and the connections where causing a short to ground that was lowering power to the bcm. I removed that and fixed wires. At that point the car would start again but still wouldnt shift and I had the power steering message. I tried adding the tcm ground.. nothing. The tcm ground is a Chevy tsb that can prevent you from arcing the tcm during jump starts and can help some issues. But really all you are doing is covering for a poor ground. If you remove the connector from the tcm there is a large pin on one side use an ohm meter and test for a good ground from that pin to ground.. if you find it is not good the ground is located on the strut tower right behind the fuse box under the hood. Clean it or replace the loop. I also tested all the powers in this connector and found a lower voltage on the pin 31. I checked power at the fuse and found it was low. I replaced the bcm at this point. The bcm needs to be programmed. You can do the 30 minute key relearn to bypass the theft issue but you must reprogram to get the correct functions. Now all the powers and grounds were good. But I still had that 64 ohms. At this time I noticed a few things... the trunk pop didnít work and the tail lights didnít work. Also my son was always complaining about his speakers making noise. After studying wire diagrams I removed the seats and rugs and chased wires. Every thing looked good at first but after opening up the tape there is a splice for the tail lights inside the harness. It is right around where the wires curve toward the back seat under the drivers seat. The splice pack corroded because the rug was soaked from his sun roof drain not working right and pouring water into his car. When I was fixing the wires and got the tail lights working I also noticed they had been arcing and damaged the speaker wires and the trunk pop wire. I also noticed the data wires going to the communication module in the rear deck lid and been damaged. After fixing all those wires everything Was back to working... my data lines ohms were at a perfect 60. I still had no communication with the tcm and the power steering message. The steering module looks for a speed input from the tcm. All the problems I found one of them must have shorted the tcm. I got a used one from the junk yard and again this is a module that you must program. After reprogramming the car works perfectly. Sorry I donít have pictures of all this but all of these things and videos are easily googled. I hope this post can help anyone facing any of these problems. Again the Chevy system is very sensitive to good connections use electric grease on all the connections you take apart and donít thing close enough is good enough... you need good grounds proper voltage and the exact ohms for it to function properly

---------- Post added at 05:27 AM ---------- Previous post was at 04:39 AM ----------

Sorry forgot to mention when he called me to say the problems he had he shut the car off and it wouldnít start again
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post #2 of 4 (permalink) Old 03-04-2018, 08:13 AM
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After repairing the harness did you re-install the old BCM to see if it was good?

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post #3 of 4 (permalink) Old 03-04-2018, 08:22 AM Thread Starter
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Originally Posted by Coby7 View Post
After repairing the harness did you re-install the old BCM to see if it was good?
I didnít. The bcm power seemed to be ok after the replacement. I believe it was 2 desperate conditions. Each thing I fixed or replaced seemed to correct some problem but not all.
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post #4 of 4 (permalink) Old 03-04-2018, 09:35 PM
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Good going Bamb waiting on updates.

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