I have felt compelled to tell others in this forum for a possible solution to 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’s solution (albeit for Power Steering, but I believe uses the same kind of pressure sensor):
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. Prior to us buying, my daughter’s car had the ignition recall fix and the power steering motor recall fix. Just a few weeks ago, we went to the dealer who said the Power Steering module/column needed 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 many hours troubleshooting after it started acting up again and I finally got this solution!!