Somorazach

I have a 2003 mustang gt and I was recently checking under the car and noticed that the passenger upstream oxygen sensor was dangling and unplugged and melting on the exhaust pipe. I jacked the car up replaced the oxygen sensor and could not figure out where to plug it into, and let me tell you I reached up over the bell housing of the tranny to find the plug but I cannot find it, the other upstream is plugged in and working properly. After I jacked the car back down I went over to where my Freon reservoir is (or whatever you call it) and there's a square plug with a brass bolt right there next to it i unplugged it to free up some space so I could look for a plug for the o2 sensor. Still cannot find it. After about an hour I stopped searching and plugged everything back in. Including the square plug with the bolt. I go to start the car. It starts and runs for about 1 second then dies. Tried to start it again and does not start after trying a few more times it finally starts and runs fine. But when I turn the key off the gauges don't move and the odometer reads dashes no theft light is blinking. I put gas in cause it was low on gas and it starts up fine no problems but once the car shuts off the gauges stay where they are as if the car is on still then about 1 second later they go down all except the battery gauge and the odo reads dashes again. Now this is when the key is out and the car is off. I let it sit for at least 20 minutes and the odo reads dashes still. I'm afraid it's gonna kill my battery so I unplug the battery and let it sit. Plug it back in and still does the same. Now keep in mind it isn't a pats problem cause my car does start. I've checked all fuzes grounds and wires and nothing is unplugged. Please help!!!!!

08'MustangDude

The odometer reading dashes means it has no communication with PCM, or a bad cluster.

If these are anything like some of the newer cars, the O2 sensors are wired directly to the ECU, and
any shorts will damage it. SO, if it was dangling there, and melted, power to the sensor harness could
have shorted to the exhaust, and damaged the ECU, or blew a fuse at the very least. I know you
said you checked them all.... In the CCRM as well?

So, basically, a cluster with all "-" means that it does not "see" the ECU.I let off the fuel pedal, all the gauges go to rest, and I get dashes in the odometer
display. As soon as I apply the fuel pedal, it wakes up... The dongle is interfering
with communications to the ECM at random, which is weird...

You definitely have a comms problem between the cluster and ECU.

Somorazach

hmm well when i checked the 02 sensor it wasn't even plugged into anything so I searched for the plug that it goes to and I could not for the life of me find where it plugs into. I can't get past second gear now as well it acts like it wants to die if I shift into third and I just replaced the iac as well and it revs really weird if I touch the gas it will go above about 2000 rpms and then back down to 1500 stay there for 3 seconds and then go to abo it 700 then up to 8 or 9. I'm very frustrated with the car and it's my first gt