Chasing engine codes in a 2011, base model HHR. Just looking for input to see if I'm going down the right path the address these 3;

P0102 (volume air flow low A circuit or A circuit low input). This car has 235k miles on it and I installed a new MAF sensor (which cleared a previous code) after cleaning and recleaning the original MAF : ). I also cleaned the throttle body (TB) and installed a new air filter (although the original was fine). I'm planning to replace the MAP sensor for this code. Does that make sense?



P0420 (Below threshold bank 1 Catalyst system)

P0171 (Bank 1 system too lean)

These 2 codes got me started on this car. When I started it up I could hear an exhaust leak and the inside of the car had a slight exhaust smell. Checked the exhaust system and it was a complete rusty disaster and there was a leak at that flex pipe. Took it to a muffler shop and had the entire exhaust system replaced. It's all nice and solid now but still getting these codes.

I was thinking of replacing the upstream 02 sensor. Then I thought, wait a minute there is no code identifying that as the (an) issue and I'm not a fan of just throwing parts at a problem.



I'd appreciate any thoughts you may have for my plans to replace the MAP sensor (looks original) and whether replacing one, or both, 02 sensors is a good idea since the cat is new.

 

Check the exhaust manifold under the heat shield it might be cracked. Usually the P0420 indicates a clogged catalytic converter.
check for air leaks before the MAF is the new MAF installed in the correct direction and sealed against the mounting flange?

 

To be more precise, P0171 doesn’t mean it’s running lean. It means that upon reaching close loop, the ECU is successfully compensating for a lean condition, but thinks that the necessary compensation is excessive.

Any sign of fuel or evap system leaks? Do you turn the car of when refueling? Have you refueled since you attacked these issues? Does the car make a lot of short trips? Do you ever fuel with E85? Is the battery fresh strong?

 

Cracked flex pipe.

 

That was replaced in post #1 Donbrew. I’m wondering if the catalytic converter was replaced or just welded to ?

 

That MAF sensor only goes in one way so the direction is good. I cranked down on the 2 screws pretty good but will double check.

 

No sign of evap system leaks at least there are no codes beyond the ones I listed. I always turn off the car when refueling. I have refueled since attacking the issues. Very few short trips. I do refuel with E85 on occasion. I just installed a new alternator and haven't checked on the battery since. Will check it this afternoon to see if it shows 12V at rest.

 

That entire exhaust system was replaced and that included the cat-con. I don't hear or smell any leaks but will put it up on ramps and check under there.

 

To check the exhaust manifold, remove the air filter box, remove the 3 bolts holding down the heat shield and you do this from above.


The heat shield

Biden crack

 

Okay I replaced the MAP sensor (that was easy), Cleaned the connectors for MAP and the MAF sensors. I also replaced the air intake hose ( it had seen better days and in the interest of properly flowing air, figured it couldn't hurt) and I changed plugs (don't laugh. I had no idea how old they were. The plugs I pulled looked great. Brown tips, nothing wet. I could've put them back in, lol). Cleared codes and went for a 30 mile test drive and no lights. However, that doesn't mean much. I've experienced, more than once, taking a drive that long and then the light comes on after a restart.

I still need to double check that the MAF sensor is screwed down tight. I'd have done it while I was replacing the MAP sensor but my torx set went missing. Will snag a set in the morning and do that quick check.