I gave you your plausible causes, start there as they don’t cost anything!

 

Thanks, Oldblue! I believe I misunderstood your original statement bolded above to mean all 4 "sensor connectors" weren't connected to the hubs, but I believe you were saying the problem wasn't related/connected to the hubs being defective. Let me know if I'm off base here and my apologies for missing that important detail. Below are the things I've checked so far regarding the ABS/Traction Control messages. The ABS, Traction Control and Brake lights are all constantly on at startup and while driving; they never go off. If you see something I've missed, please let me know. Thanks again!

1. Replaced faulty battery. Was really hoping after 2-3 short driving sessions, this would have magically fixed it.
2. Checked fuses in engine fuse box. Based on the diagram under the fuse box cover, I believe I have checked them all by pulling them out and testing visually and with a continuity test on my multimeter. I will go through these again just to make sure I didn't miss anything.
3. Tightened the 4 engine fuse box bolts tighter to ensure they are making a good connection. Don't want to strip them so stopped when I thought they felt about right.
4. Tightened the battery ground and the ground wire right next to the engine fuse box.
5. Visually checked what I think are the ABS wires going to the front right and front left wheel hubs. Found where the passenger one and driver side were coming from inside and going out the wheel well to the hub so pretty sure those are the correct ones and they both looked intact.
6. Disconnected and reconnected the front right and front left ABS wiring connectors at the wheel hubs. Testing continuity on the ABS plug ground wires in the wheel hub connector to another ground point in the engine bay, and they both read the same. At that point I didn't record the value sine the left front wasn't reporting an error code, but I will double check this again to see the values and see if they make sense. If they aren't getting a good connection to ground there, other ground points could be a good place to focus, I think.

 

Sounds to me like chasing rabbits, my experience with abs codes concluded the hubs had internal problems, replacing them resolved the codes. Can they all fail? Depends on their age and time sitting, the speed sensors could have internal issues.

 

Yeah I’m going to kick that ABS can down the road and deal with it last I guess. Chasing rabbits is no fun. Thanks for your help.

I completed the valve cover gasket, including all pain in the butt bolt grommets, replaced the spark plugs, and put new plug boots on since the pack of 4 boots was pretty cheap. I’m pretty happy with my progress. However, the pcv vent hose going from the valve cover to the air intake is cracked on both ends. I was able to get it back together pretty good but not sure how good that seal needs to be. Should I replace the hose or just let it ride? No codes( other than the abs issues) on first drive and seemed to run a bit smoother.

 

Replace the hose, unmetered air will cause engine issues.

 

That is very interesting to me. It seems the OEM thermostat failed in just 3 years? Were they identical in appearance back then also? If so, it makes me curious as to how two thermostats of identical design could open at different rates.

One awkward reality in the parts world is that sometimes, when an OEM rejects a parts shipment, they get sold into the replacement market. Sometimes, ORMs use statistical methods to inspect parts shipments. Sometimes the supplier simply reships rejected lots, hoping for a luckier sample in the testing process. True story. Does it still happen? I have no idea. Source - I worked for an automotive parts manufacturer.

Maybe thermostat manufacturing has improved in 15 years. Maybe it's gotten worse.

 

My OEM thermostat back then had the black rubber ring distorted and keeping the thermostat open. The aftermarket thermostat had the same rubber ring in the centre, the AC Delco 131-158 did not have the rubber ring

 

Ordered the hose replacement from Walmart for $19. Thanks!

Drained and filled the coolant yesterday, but only got maybe a little over 3 quarts out. Plus, the dang drain plug doesn't have a clear shot down so a bit of spraying and running off the sides happened. I'm guessing that is why the SS Coolant drain tutorial stated to remove the metal bracket holding that corner of the radiator so the radiator can be tilted to allow the coolant to drain straight into a container. I then filled it up to the top of the pressure cap and took it for a drive where it got up to around 200 degrees and then came back down a bit. When I parked on my sloped drive with the nose tilted up, I could have sworn I heard some gurgling water sound, so I wonder if that was the coolant coming back into some of the parts that were a bit empty and some air escaping? Maybe just hearing things. LOL I let it sit overnight with the nose up and will take a look at it later. Just because it's so easy and the premixed dexcool is so cheap, I might do another drain and fill after several driving cycles to get even more fresh coolant in there. Got below freezing last night so I'm glad I used the premixed 50/50 coolant instead of the water and concentrated dexcool. :)

Switching gears to the ABS/Traction Control/Brake lights always on the dash, can someone please confirm the ground points I should double check that the ABS/Traction System/Brake light combo could be related to? So far, I think I should check G111, G105 and G110; does that sound right? I'm using the awesome resource created by @donbrew at https://www.chevyhhr.net/forums/members/donbrew-13699/ to learn the ground locations and for guidance in finding them. Thanks, donbrew!

 

There is a link in my sig to FREE shop manuals. charm.li

 

Yes, I downloaded it and then found the LE8 ground/wiring diagrams for my 2010 HHR LS. Printed them off, mainly all the G100-199 points since I "think" those are the only ones that could impact the ABS/Traction Control/Brake lights being on. The plan is to check each of them before I mess with all wheel speed sensors or the ABS module itself. I looked at the ABS module and I wasn't able to easily figure out how to unplug it, since I wanted to do the standard unplug/plug back in again trick. I will look at the shop manuals for guidance on getting the wiring harness off the ABS module. Again, thanks for providing those as they are very helpful.