Chevy Cobalt Forum banner

Status
Not open for further replies.
1 - 18 of 18 Posts

·
Registered
Joined
·
34 Posts
Discussion Starter #1
I'm still having intermittent gauge problems with DIC indicating things like Low Fuel and Power Steering. This all started about 2 weeks after the power steering motor was replaced in the recall. Also transmission hard shifting is usually one of the problems that come with this.
About 3 months ago I removed every connection to the ECM, BCM, TCM and Fuse block, cleaned with electronic connector cleaner and applied dielectric grease, then reconnected. Everything seemed to clear up except hard shifting. I took it into Chevrolet for diagnostics. Car had almost 40000 miles on it.
Problems was diagnosed to be the internal transmission harness had high resistance. When they removed the harness they told me it looked like something has smashed a section of the harness. After replacing the harness the transmission shifted normally and no more intermittent problems... for about 3 months, then everything started again. This has been going on now for about 20k miles. Sometimes turning off the car and restarting it will correct everything including hard shifting and sometimes the hard shifting is still there until an extended time before restarting. I've read that the ignition switch in the steering column, not ignition cylinder, can cause this if it is becoming intermittent in applying 5Volts to the computer buss. I've bought an AC Delco ignition switch but have been hesitant to replace it for fear that the anti-theft system will need to be reset with a Tech-2 scanner.

Can someone let me know if I can change the ignition switch without requiring a trip to the dealer after replacement on the back of a wrecker?
 

·
Super Moderator
Joined
·
11,821 Posts
Disconnect Your battery, change the switch and re-connect, then you should have no problem with the "TDM". If you still have hard shift problems after this, try cleaning the ground terminal (G105) on your engine or at least making sure it is tight.

Low fuel is probably a seperate problem. GM has a solvent you add to a full gas tank that cleans the sending unit and clears the intermittents that cause your low fuel indication to come on.
 

·
Registered
Joined
·
34 Posts
Discussion Starter #3
Thanks Coby7. Is G105 on the front drivers side of the engine?
I'm going to change the switch this weekend if nothing more pressing comes up. :)
 

·
Super Moderator
Joined
·
11,821 Posts

 

·
Registered
Joined
·
34 Posts
Discussion Starter #6
I found instructions for replacing the lock cylinder on AutoZones website but could not find instructions for replacing the switch itself. I assume to replace the switch I have to remove the lock cylinder, then remove the switch. Is there any additional dis-assembly required beyond the lock cylinder before I can access the switch?
 

·
Super Moderator
Joined
·
11,821 Posts
I will look it up when I get home. Seems to me you don't have to pull the cylinder. It just sits on the end held in with two screws.
 

·
Super Moderator
Joined
·
11,821 Posts
Here is the how to from the GM service manual that I just downloaded. READ THE LAST PART


---------- Post added at 10:30 PM ---------- Previous post was at 10:11 PM ----------

30-Minute Immobilizer Relearn
This 30-minute relearn procedure will relearn the start enable password between the theft deterrent module (TDM) and the engine control module (ECM).

With a master vehicle key, turn ON the ignition, with the engine OFF.
Observe the security indicator. After approximately 10 minutes, the telltale will turn OFF.
Turn OFF the ignition, and wait 5 seconds.
Repeat steps 1-3 two more times for a total of 3 cycles or 30 minutes.
Important: The vehicle learns the password on the ignition switch transition from OFF to RUN. You must turn the ignition OFF before attempting to start the vehicle.

With a master vehicle key, start the vehicle. The vehicle has now learned the key transponder information and/or the ECM has now learned the fuel continue password.
If additional keys are required to be learned, refer to Adding Keys .
With a scan tool, clear any DTCs.
 

·
Registered
Joined
·
34 Posts
Discussion Starter #9
Is the master vehicle key something that only dealers have or is it one of the keys that came with the car?
 

·
Super Moderator
Joined
·
11,821 Posts
Yes, that is all the keys programmed that you normally use to start your car.
 

·
Registered
Joined
·
34 Posts
Discussion Starter #12
I changed the switch Saturday. So far, it's good. I didn't work on the ground. Wanted to do one thing at a time so I would know which repair fixed the intermittent problems.
Thanks for the help.
 

·
Super Moderator
Joined
·
11,821 Posts
How did it go with the relearn or was it necessary?
 

·
Registered
Joined
·
34 Posts
Discussion Starter #14
I didn't have to do the relearn. It wasn't too difficult to change the switch.
The bad news is that it didn't help. Still intermittent. I'm going to clean the ground connection tomorrow.
 

·
Registered
Joined
·
34 Posts
Cleaned the ground on the left side of the engine and still didn't help. Today it set a P2127 code. My code reader shows "P2127 throttle/Pedal Position Sensor/Switch "E" Circuit Low.
Does this mean the sensor is bad or something else causing it? Any ideas where to start troubleshooting this?
 

·
Super Moderator
Joined
·
11,821 Posts
Valid Cobalt code. If P2127 is set alone with no other codes, this does not mean your APP sensor is at fault. The sensor comprises of two rheostats with +5 reference volts on one side and a .2 volt low level reference on the other sides with the center wipers being your position sense controls. P2127 means that your ECM has detected for more than 20 seconds that on of the low reference of one of the sensors is less than .13 volts.

So my guess is a low reference voltage wire is touching ground somewhere between the sensor and the ECM.

But more info is needed for a more precise diagnostic. Info from yellow box is in next drawing for better understanding.


 

·
Premium Member
Joined
·
3,700 Posts
I fixed a similar problem by cleaning G101. Right under the coolant resevoir on my 07 L61. Copper ground under coolant... genius. Not possitive thats your issue. But a semi easy cleaning, with no need to probe connectors. Only p.i.t.a is I needed to lift the underhood fuse block enough to clear the mounting stud they share. You can look under the coolant reservoir with a flashlightto see if the ground is corroded first. Not saying its a perfect fix, since the e.p.s has its own ground. But it is bussed through other modules. And my issue has not returned since the cleaning about 4 months ago.
 

·
Registered
Joined
·
34 Posts
Discussion Starter #18
Think I may have found the problem with the P2127 code. The car had been wrecked and repaired before I bought it. After I started having the intermittent problems and started investigating I found that the top ECM connector backshell was broken and one side of the latch was missing. Only the bottom latch holds the connector onto the ECM. Yesterday I was going to re-seat that connector and when I removed the cover over the ECM I saw that the latch had backed out and was not holding the connector securely. I had not been able to get the code to clear by disconnecting the battery, but after pushing the latch back down, I reconnected the battery again and that problem was resolved. That connector may be what has been causing the intermittent problems for the last 15K miles. I would like to replace the backshell but it looks like the connector may have to be replaced to get a new backshell. I'm going to try a temporary solution to hold the top of the connector in place for an extended period to see if that fixes the problem. I will be a very happy camper if that works!!!!
 
1 - 18 of 18 Posts
Status
Not open for further replies.
Top