2006 Chevy Cobalt with electrical communication issues (TCM, ECM, BCM) Pt. 2

via YouTube Capture

[spikedspike]

MYSTERY %$#&**%$ SOLVED!!

Cobalt owners with following symptoms: while driving, the dreaded “ding ding” sound followed by security light coming on dash, gauges go wonky (speedo, fuel and rpms bounce to zero and back) Power Steering light may come on, sometimes jerky auto transmission shifting, sometimes loss of Power Steering and/or car going into Limp Mode.

My daughter has had her 2008 Cobalt Coupe for less than a year, we bought it used with about 110K miles on it. I have been troubleshooting trying to fix this issue since around the time she got it, like many of you, to no avail. I have spent hours researching on the internet (thank you to all of you Cobalt Warriors who have been hounding this too, with all your great info) as well as inspecting, cleaning contacts, looking for possible reasons for an electrical short - as many have found the fault codes almost always show loss of communication codes, but are unable to find the problem.

This may not be the only reason this happens, but I’m fairly certain this is why it was happening to my daughter’s car. Please check the following on your car to see if it has the same thing:

1) Inspect Oil Pressure Sending Unit for oily residue on outside (I know, you’re saying “what? why?”)
2) Inspect Connectors to modules, lower PCM especially, but TCM and upper PCM too, for any brownish oil residue on connectors or on the modules themselves – where pins are and around inside edges of modules, right where the connectors attach.

I believe what is happening, and bear with me…is that the Engine Oil Pressure Sensor begins to leak (fail)…and then oil from your engine is expelled under very light pressure out the Engine Oil Pressure Sensor …where it doesn’t fall below by gravity like you would expect…it travels like an alien species along the sensor wire and wire harness, even uphill, and around harness bends, until it makes its way to the module…in my case, the PCM. I believe it is the oil in the connectors making contact with the pins or the module itself to create an intermittent and temporary short, which makes you experience all the crazy Cobalt symptoms described above.

I finally came across the solution after Googling “oil in PCM”, and found other people who found oil in their PCM…These cars were not Cobalts or even GM cars, which one would normally discount as not being applicable. But if you read their threads below, you will see that they maintain that oil can travel from a leaking Engine Oil Pressure Sensor or a leaking Power Steering sensor, along harness wires to reach the PCM…they have similar experiences with the their cars’ gauges going haywire and transmissions not working correctly. See these threads:

Dodge Neon: Read Moderator Chris Barrett’s solution (he also noted it usually happens with weather proof (sealed) connectors..Maybe it is the suction created by the end connector seal to cause the oil to run along the wire:


Dodge Durango: read Getpaidct solution (albeit due to Power Steering sensor, but must use same technology):


Note: If your Engine Oil Pressure Sensor looks suspect and is oily, you may not yet notice any oil in the PCM module, connector area…I didn’t the first time I inspected it…I originally cleaned the connector and module/pins with CRC electrical contact cleaner spray, which seemed to help the problem go away for a few months. But the second time I inspected the connection, there was oil in there…I couldn’t figure out how oil was getting in there, as the contact spray should have completely evaporated, and it was just a wire harness ending with a plastic connector (with female connectors for pins) and the module, which was sealed in aluminum, with just copper pins sticking out of the module.

TO FIX: disconnect positive and negative battery terminals. Replace leaking Engine Oil Pressure Sensor, located on the engine block, down low, facing the right center of the front bumper (car needs to be raised to gain access from below) . Remove PCM and TCM module connectors. Remove outer black plastic cover of connectors. Generously spray harness wires near connector and both sides of connectors, where wires go into connector and the outer female leads with Isopropyl alcohol, something to cut through and clean off the oil. Use compressed air to blow out any remaining alcohol from both sides of the connector. Also clean pins and connector area on modules the same way. When confident everything is completely dry, re-attach connectors to modules. Before connecting battery, touch both negative and positive battery leads together for at least 15 seconds, to clear any residual stored codes. Re-attach positive battery lead, then negative lead. Hopefully your Cobalt electric gremlin has been exorcised forever, like mine!

If this is not the answer for your Cobalt troubles, check for possible wire breaks on the G105 ground bolted on the outer transmission, which is located on the top side of the transmission facing the front bumper. There was a moderator on CarGurus who found a stress break on his G105 grounded wires, which was causing the same symptoms and was resolved when the grounded wires were fixed appropriately. The picture of his ground did not include a larger ground strap, which my daughter’s car had, that looks original. My guess is that GM added the extra strap to the 2008 model, after finding the weakness or stress failure of the ground in the 2007 and earlier models. Some Cobalt owners have said their troubles were fixed after the dealer found a break in a wire underneath the car, and I’m guessing this is where it was, as I was not able to find any other possible wires to check, outside of the wires going through the firewall to the engine compartment.

Also, one of the first things I did, and still have, was to ground the TCM to the car body left strut, like many people have recommended, although it didn’t solve my problems like it did for others. My daughter’s car also had the ignition recall fix, the power steering motor recall fix, and then we had the Power Steering module/column replaced, which the dealer said was the problem for all the above symptoms, but it fixed it for only a few days before returning. I spent a good 4 hours troubleshooting after it started acting up again and I finally got this solution!!

[vincehair]

for any1 w/same issues, its a ground wire problem at the engine bolck and/or a bad/corroded fuse on the bcm fuse block located right side of console

[berniecormier]

Hello, I’m having the same thing going on with my 2007 Cobalt ls…so what did you end up changing?I’ve been thinking about replacing my ecm.

[devantemitchem]

I have a 2010 Chevy cobalt I’m having close to the same problem I have put in a new pcm it’s nun of the gauges work and there’s no crank not even turning over I checked all the fuses they are getting power no crank just clicks what should I do next and there’s no check engine light on

[martyomaya]

Ive got a 2007..i juss learned how to deal with it and learn how to drive it... Shits payed for..hehehehe

[HauahYqjaia]

Mi cobal tiene el problema que las agujas o testigos de combustible, revoluciones y velocímetro suben y bajan la dirección se coloca dura y cuando hace los cambios suena

[austinkraemer]

I have a 07 Chevy cobalt as supercharged lately when I come to a stop the power steering light comes on and my Gage's go to 0 after couple seconds it resets what could this be

[brianarrington]

My car has had this problem since 40k miles. It now has over 70k miles. Ill be driving down the interstate and the power steering will go out. This isnt safe, but when I called GM they said "tough luck". Report your problem to NHTSA at 18883273246 if they receive enough complaints GM will be forced to issue a recall.

[Mrs.NiceGirl]

I have the same problems. But mine jumped nearly 1500 miles in two days of only driving for 30 minutes each

[robt]

This is a follow up video to my first one found here:


This is all meant to tie into all the electric problems we encountered with our 06 cobalt and how we got them fixed.

Click the link below to read up on what lead to this problem and how we got it fixed properly.

Remember don't be affairs to ask questions. Scanners only tell you there is a problem and not necessarily what the root cause of the problem. Find a mechanic who is willing to take the proper time and troubleshoot. Throwing parts at problems is not the way to fix issues like this.

[shawnbrooks]

G105 Transmission Ground Location:

Old connection:

(1)New connection:

(2)TCM Additional Ground:


(3)EXH Fuse Location: (supplies voltage to HO² sensors, MAP, cam sensors)
If it keeps blowing check for short around oil filter, rear O2 sensor, etc.

I re-grounded the G105 transmission ground (1) and then I removed the TCM ground (2), issue appears to be fixed.
The car was still shifting hard and would immediately throw the P0443, P0102, P0030 codes which was due to a blown EXH 10a fuse (3). As soon as the fuse was replaced, everything ran like butter. I'm assuming the fuse blew because of the previously bad G105 transmission ground since its all related.

[robt]

Part 1 when the trouble started can be found here:


...Along with the link to the forums on what happen from start to finish and how it got fixed.