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This is my first time posting although I have read alot of great information on here. First, I am no mechanic by no means. I need some help with my Impala.

I have a 2008 Chevy Impala SS 5.3L V8 engine. I bought the car used and know it wasn't well taken care of.

Anyway, these are my issues.
1)I have a coolant leak. When it was pressure tested, there was steam coming out where the water pump is. I haven't had the water pump replaced yet, but have a new water pump, thermostat, and temperature sensor to see if it helps. I had a message which sense went away, Engine Hot/AC Off with the code PO128 hence the thermostat and temperature sensor.
Sometimes I have no heat and other times I got more than enough.
2) Broken Sway Bar which to my understanding is a common problem with this car. I had it welded as a temporary fix when I had a new cat put in because the PO420 code kept coming off and on. Last night, I got the code again so not sure what is going on there.
3) Tranny Problem Possible. Sometimes it will slip or shift hard. The tranny fluid smells burnt. The throttle body was cleaned and tightened up like it should have been in the beginning. It has helped the transmission some and has stopped the hard shift and slip to where it doesn't do it as often.
4) Service Traction Control, Brake Assist, and Stabitrak message with yellow ABS light with the
Code C0040-0F and Code C0040-00.
I have no idea what is causing this other than what I have already read on here. Wheel Speed Sensor which means new hub, broken wire, bad connection, etc. It seems like the wheel is locking up to keep the car from moving when at a dead stop. Then I might move about 2 inches and the car does it again. Then I could be driving then my Impala acts like there is nothing wrong at all, but I know better. It also feels like something is getting in a bind and won't let the wheel move. It sometimes makes a noise, but it isn't metal to metal This morning on my way home from work, it was a metal to metal sound. Sometimes the sound does not throw the messages. Other times it will. For this problem, not sure where to begin to make it right or if this is part of a bad transmission.
5) Oil Leak Possible. My oil is going somewhere or the motor is using it. Not sure which one it is.
6) AC and Heat Issue. The passenger side works just fine, but the driver's side sometimes works and other times it does not. For the time being, this is the least of my worries.

Any help would be greatly appreciated. If I posted in the wrong place, I apologise in advance as it is my first time posting.
 

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1 A) Coolant leak. Check for plastic elbows. The old 3.8 V6 is famous for leaking plastic coolant elbows and o-rings on the water pump. I have yet to have leaks so I have no experience with my LS4 in this area. The water pump is a likely culprit but be sure to check your hoses for leaks as well.

1 B) The intermittent heat is likely an air bubble in the cooling system. Be sure to bleed the cooling system. I park nose up on a steep rise or jack the nose way up in the air and fill the cooling system with the engine running and heat turned on full blast. These engines use Prestone Dexcool. Don't mix with the old silicate stuff. Just buy the 50:50 bottles of Dexcool at wally world. I would still park it nose up on a steep incline or jack the nose way up in the air when using a vacuum bleed and fill tool.

2 A) Broken sway bar. Replace with the Dorman 927-100 swaybar. Use the Moog poly end links and Energy suspension poly bushings. Look in the suspension sub-forum for the end link and bushing part numbers.
You may want to install the Addco rear swaybar with Moog Poly bushings and install strut tower tie bars as well. These aren't terribly difficult jobs in comparison to the front swaybar and they make a huge difference in the driving manners in curves.

2 B) P0420 is a Catalyst efficiency code. This may be O2 sensors or mixture issues. A lot of things affect your fuel air mixture.
This is a jumping off point. Depends on how far down the rabbithole you want to go.
I would log your O2 sensors to see how they are performing.
If they appear to be malfunctioning I would look over the wiring to make sure your parts changers actually plugged them in properly and routed the wires such that they don't burn on the exhaust.
If the O2 sensors appear to be operating then check your fuel trims and injector pulse widths.

3 Change your transmission fluid out with fresh Dexron VI and do the pan magnet TSB. I posted the transmission pan magnet TSB in the forum so you should be able to find it. Your 4T65E-HD may be on the way out but it's worth a shot to try and wring a little more life out of it. Likely the TCC and PCS solenoids are iron poisoned but you can get a little more life.

4 Traction control C0040-00 is a fault in the RF wheel speed sensor circuit. The wires breaking between the ABS sensors and body is common enough that a repair pigtail is available.
I would check the resistance of the wheel sensor... It should be between 800Ω and 2KΩ. IIRC the W body sensors are around 1.5KΩ.
Unplugged sensors will generate an AC waveform across the ABS sensor coil that you can view on a portable oscilloscope when you raise the tire and spin the wheel.

5 The LS4 uses oil.
Mine is worse with some brands than others and it eats more after I clear about 5K miles on a change. Switch brands of 5W30 and change the oil and filter before you get to 5,000 miles.
If you have a pan leak make sure you look up the LS4 oil consumption TSB. GM re-designed the pan gasket to shroud the oil spray from the AFM lifter return gallery.
Obviously look over the valve cover gaskets.

6 Check your blend temperature door motors.
 
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From my past experience working on transmissions it sounds like your clutch bands are burning up for some reason. Have you checked to see what the transmission fluid looks like currently? BTW make sure you read this if you end up having to make the decision between rebuilding a transmission or buying a replacement Transmissions 101 Blog
 

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The 4T65E burns up the Torque Converter Clutch and the clutch apply paks.
This happens from two failures.
1) The transmission fluid temperature is typically around 200°F because most of the W Body cars do not have a transmission cooler between the radiator and the transmission fluid return. 180°F is about as high as you want ATF to run for any length of time. 181°F and higher will cause longevity issues. The 9C1 9C3 Taxi/Police package cars have fluid cooler that can be fitted to the Base, LS, LT, LTZ, and SS models to lower the trans fluid temps. The mounting holes for the cooler are present in all of the Impala bodies.

2) The 150°F magnet GM put in the pans wasn't rated for the operating temp in a transmission. Magnets permanently loose field strength when they are heated past the max operating temps. This magnetic field degradation causes the electromagnetic control solenoids to have more affinity for the iron in the ATF than the magnet intended to clear the iron out of the ATF. Higher temp magnets are available from GM. The TSB calls for the magnet used on the Allison and Saturn spin-on transmission filters.
The iron on the control solenoids creates a ferrite bead that screws with the ability of the PCS (pressure control solenoid) to properly regulate transmission line pressure. This affects clutch engagements... the engagement rates depend on fluid pressures in the valve body to control the rate of engagement of the the clutches with fluid gated by the 1-2 & 3-4 and TCC control solenoids. The gate solenoids poisoned by iron exhibit delayed and choppy engagement.
The Torque Converter Clutch is controlled by the TCCS (torque converter clutch solenoid). This poisoned solenoid along with low less controllable line pressure from a poisoned PCS causes accelerated TCC wear and since there's a lot less friction material than the apply paks the TCC fails first. The failing/failed TCC sheds friction material and this friction material boogers up the valve body and plugs up the pickup strainer in the transmission pan starving the pump for fluid. This accelerates wear in the apply paks and the whole thing fails.
You can install a Magnefine inline magnetic filter in the fluid return and replace this filter every 500, 1K, 5K and then 10K miles to clean up the return from the cooler(s). I would highly recommend doing this after installing a rebuilt unit. It makes a good preventative before you have a failure to extend the lifespan of your transmission.
You should replace the original magnet following the GM 4T65E pan magnet TSB recommendations.
 
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