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So, I recently bought this 2011 HHR 2.2L LT. Found I have a P0172 code with engine light. I inspected and also cleaned the MAF sensor, but someone here mentioned the flex pipe may be cracked. Well, something was cracked alright. But it was the exhaust manifold instead. Good thing I went to check it out. Now my other issue I have is my catalytic converter too. Owner said mechanic accidentally welded the upstream o2 sensor so they made another hole and welded another o2 sensor in there. And if I’m seeing right, their are 3 sensors connected onto the cat converter. But of course only 2 are plugged in. The downstream sensor looks like it hasn’t been tampered with. But in all honesty, is it worth messing with this or should I get a new cat converter and start over? I know now I need a new exhaust manifold
Well, I don't think it has anything to do with the code but i would steer clear of someone that calls himself a mechanic that made that mess. Are the 2 sensors before or after the cat?
If they are before the cat that hole he blew through the closest one could cause P0172. I wonder why he didn't just put a bolt in the bung.
The design of O2 sensors actually allows a flow of air from the top where the wires are to the exhaust flow. A big hole like that could let too much air in.
So, I recently bought this 2011 HHR 2.2L LT. Found I have a P0172 code with engine light. I inspected and also cleaned the MAF sensor, but someone here mentioned the flex pipe may be cracked. Well, something was cracked alright. But it was the exhaust manifold instead. Good thing I went to check it out. Now my other issue I have is my catalytic converter too. Owner said mechanic accidentally welded the upstream o2 sensor so they made another hole and welded another o2 sensor in there. And if I’m seeing right, their are 3 sensors connected onto the cat converter. But of course only 2 are plugged in. The downstream sensor looks like it hasn’t been tampered with. But in all honesty, is it worth messing with this or should I get a new cat converter and start over? I know now I need a new exhaust manifold
Your code P0172 is for a rich condition not lean which is P0171. Check your fuel pressure. The sensor that is next to the one they installed is just a plug for the bung.
Those guys that did that work need to improve vastly to become mediocre mechanics.
Read the names of the P0172 & P0171 again. Don't leave the word "TRIM" out when you read it.
When a trim is rich that means the computer thinks the AF is lean. Thus unmetered air looks like the AF is lean so the computer enriches the mixture.
Right. Now that I look at that again it would seem the old sensor is leaking right next to it's replacement and that one looks like it was installed with two seal washers or something funny.
I would always do a quick FP check with either of those codes.
How is the car behaving at startup and when warmed up?
A FlexFuel Ecotec cold-starts assuming an ethanol % stored in the ECU is in the tank, because the #1 O2 sensor is needed to verify that the a/f is correct, but the O2 sensor doesn’t work until it heats up. This is called “open loop” operation. Once warm enough, “closed loop” begins; the ECM starts reading signals from the O2 sensor and adjusting/correcting the fuel mixture. This is called “fuel trim.”
The P0172 means the ECM thinks the fuel trim needed to reduce a rich condition to a correct mix is excessive.
Here is my P0172 story in a nutshell:
My 2011 2.2 started will difficulty and made black smoke and sputtered and smelled like fuel at cold start, obviously way too rich. After just a couple of minutes when it only had just begun to warm up, it corrected itself and ran fine. It threw a P0172.
In my case, the ECM erroneously thought it had over 50% ethanol in the tank when it just had plain ol’ E10. The fuel sampled at 11%. This is a fairly rare but documented problem in GM FlexFuel cars and trucks in which for some reason unknown, the ECM gets confused. There is a TSB on it. Per that TSB, I had the dealer reset the ethanol % to zero, an it cured the problem instantly, and it never happened again. The car eventually set itself to 10% or so.
Clearing the codes or disconnecting the battery will NOT reset the stored ethanol %.
No one seems to know exactly why this happens, but there seems to be a long lists of conditions that may be preset when it does:
Frequent short trips
Leak in the fuel or evap line
Recent refueling
Onset of cold weather
Exhaust leak before the #1 O2 sensor
Failing to turn off the car when fueling
Contaminated fuel, or fuel compatibility issues not yet fully understood
You seem to have at least one exhaust leak before the O2 sensor(s?). Do any other items on the list fit your situation?
Last edited by PulpFriction; Jun 30, 2022 at 09:18 AM.
How is the car behaving at startup and when warmed up?
A FlexFuel Ecotec cold-starts assuming an ethanol % stored in the ECU is in the tank, because the #1 O2 sensor is needed to verify that the a/f is correct, but the O2 sensor doesn’t work until it heats up. This is called “open loop” operation. Once warm enough, “closed loop” begins; the ECM starts reading signals from the O2 sensor and adjusting/correcting the fuel mixture. This is called “fuel trim.”
The P0172 means the ECM thinks the fuel trim needed to reduce a rich condition to a correct mix is excessive.
Here is my P0172 story in a nutshell:
My 2011 2.2 started will difficulty and made black smoke and sputtered and smelled like fuel at cold start, obviously way too rich. After just a couple of minutes when it only had just begun to warm up, it corrected itself and ran fine. It threw a P0172.
In my case, the ECM erroneously thought it had over 50% ethanol in the tank when it just had plain ol’ E10. The fuel sampled at 11%. This is a fairly rare but documented problem in GM FlexFuel cars and trucks in which for some reason unknown, the ECM gets confused. There is a TSB on it. Per that TSB, I had the dealer reset the ethanol % to zero, an it cured the problem instantly, and it never happened again. The car eventually set itself to 10% or so.
Clearing the codes or disconnecting the battery will NOT reset the ethanol %.
No one seems to know exactly why this happens, but there seems to be a long lists of conditions that may be preset when it does:
Frequent short trips
Leak in the fuel or evap line
Recent refueling
Onset of cold weather
Exhaust leak before the #1 O2 sensor
Failing to turn off the car when fueling
Contaminated fuel, or fuel compatibility issues not yet fully understood
You seem to have couple of exhaust leaks before the O2 sensor. Do any other items on the list fit your situation?
Currently the car starts up just fine. Even after warmup. No issues I’ve seen there. Aside from the crack I have in the exhaust manifold, that’s all I’ve seen. I did notice a while back when we had a freeze down here in Texas, I had an issue at startup. Took me 2-3 cranks until it turned and started up.
Right. Now that I look at that again it would seem the old sensor is leaking right next to it's replacement and that one looks like it was installed with two seal washers or something funny.
I would always do a quick FP check with either of those codes.
And I just bought a fuel tester so this will be my next thing to check. I’ll follow up with what results I get out of it.
