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Discussion Starter #1
Hello,

I have a 2009 Cobalt LS with 2.2L automatic transmission. The reverse lights don't come on when the car is in reverse. Bulbs and fuse are good. I've replaced the Neutral Safety switch (Park-Neutral-Position switch) with no luck. Rear parking and brake lights work fine. Ground at the rear harnesses are good too. There's no power at either rear harness on the green wire (which goes to the reverse light socket) when the car is in reverse. So I *assume* I need to physically trace the wires from front to back to see if there's a problem somewhere (I've read that this wire may run under the driver's seat).

I've read that the manual transmissions have a reverse light switch that plugs into the transmission and can be tested/replaced pretty easily, but it seems the automatic transmission has this reverse light function built into the PNP switch.

I know how to get to the harness that connects to the PNP switch, and I have an automotive circuit tester and a multimeter, but I'm not sure how to proceed.

I'm looking for a little advice about next steps. I'm not a mechanic or electrician, but with a little guidance, I'm hopeful I can get to the root of this one.

Thanks in advance for any help.
 

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Have you tried re-seating the connectors on the BCM?
 

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Discussion Starter #3
Thank you for the quick reply.

No, haven't tried that yet. This morning I tested for continuity from the rear socket to a few points along the wire running under the driver's seat and was able to confirm that I have continuity up to the point where the wire goes up under the dash. Then I tried to test for continuity from the connector that goes to the PNP switch and that was no good. I don't know if this is the same for my 2009, but I referenced a previous reply of yours on this board for a diagram of the PNP connector (https://www.yourcobalt.com/forums/1744010-post2.html). There was no continuity from Pin #4 (or any pin) to the reverse light wire. I'm not even sure that's a valid test though.

I'll give your suggestion a try. If you have any information on the location of the BCM that I should be checking, that would be helpful. Otherwise, I'll have a look around to find it.

The next thing I was going to try was to tap into the wire coming out of the PNP connector to see if there's voltage there when the car is in reverse. If you're suggestion doesn't work, would this be a good next-move?

Thanks again.
 

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BCM is on the passenger side of the center console. You can see a fuse icon on the plastic cover. Just pull the 2 blue gray connectors and re-seat them a few times.
 

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Discussion Starter #5
I tried re-seating both BCM connectors with no luck. I didn't do anything to them besides connect/disconnect them a couple times each. They visually looked fine - I don't see corrosion or anything, but I do have dielectric grease if you think that could help.

After re-seating the BCM connectors, I tried checking for voltage on the backup lamp supply wire coming off the PNP switch using the diagram I referenced in my previous post. Do you know if that diagram is the same for my 2009? I worked off the assumption that Pin #4 is the backup lamp supply for my car too.

The way I tested was:
*Pulled off the connector to the PNP switch and verified that the green colored wire was connected to Pin #4.
*Spliced/tapped a wire to the green wire and re-connected the connector to the switch.
*Put the car in reverse and used my circuit tester on the wire I tapped in.

The circuit tester didn't light up. Not sure what all this means as the PNP switch is new. Could wiring back to the fuse box be causing an issue? I'm not sure where the wire goes after it leaves the switch - the bundle it's in seems to turn back up towards the top of the car (fuse box?).

Thanks for you time and help so far.
 

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Discussion Starter #6
Figured out this morning that i get power to the backup lights if I either jiggle the shifter while in reverse or shift down to neutral and then back up to reverse. Going straight from park to reverse doesn't power the backup lights. I assume I need to adjust the PNP switch or linkage at the shifter? Any thoughts?
 

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Discussion Starter #7
I was able to (partially) solve my problem. My Neutral Safety Switch needed to be adjusted. I realized that putting the car in reverse did not turn the switch far enough to send voltage to the backup lights. To adjust it, I turned on the key and put the car in reverse. At this point, there was no power on Pin # 4 (backup lights). Next, I loosened the two bolts that mount the switch to the transmission and turned the body of the switch just enough to get voltage on Pin # 4 and then I tightened the mounting bolts. Now, the lights work as soon as I put the car in reverse.

The other part of my problem that I didn't completely solve was that the power from Pin # 4 was not making it all the way to the backup light sockets. There is a problem with the wiring somewhere between the switch and the sockets and I was only able to work around this by tapping into the wire at the switch and running a new piece of wire through the firewall and under the driver seat (where the wire continues on to the rear sockets). I don't know where the original wire goes after the switch before it makes it under the drivers seat and to the sockets. It's bundled with a bunch of other wires and snakes around somewhere under the hood.
 
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