Hi,
I have a 2017 Chevrolet Sonic LT, 1.8L 4-cyl (MFI DOHC) with 131,828 miles. I’ve owned it since about 54,000 miles (around 5 years). It’s currently throwing the following codes:
- P0597
- P0128 (appears 3 times on my scanner)
- P2181
- P0131
- P0171
- P0420
- The car has had P0420 (low catalyst efficiency) for a long time. More recently it has been idling rich, smelling like fuel, and running louder than normal. On my most recent drive it lost a lot of power, backfired on deceleration, and became extremely loud under acceleration (almost like a semi truck). It struggled to go over about 50 mph. Which I found strange because it wasn’t doing any of this on the drive up, we sat with the car on for about an hour waiting, but then when I merged onto the ramp to leave this all began very aggressively.
I just found that the upstream O₂ sensor extender had popped off, meaning the sensor was unplugged during that drive.
In terms of maintenance, I wasn’t perfect when I was younger, but over the last 2 years I’ve been consistent with oil changes and regular maintenance, and I’ve recently done suspension, brakes, and a cooling fan replacement (bearings failed). I have not had any major engine work done.
Parts I already have ready to install:
- Water pump
- Thermostat housing & coolant temperature sensor
- Upstream and downstream O₂ sensors
The heat and A/C are not working correctly, which makes me suspect a cooling system issue in addition to the fault codes.
My main question is:
Does this sound like a failing catalytic converter, or could the cooling system problems and O₂ sensor issues be causing these symptoms and the P0420? Or all a consequence of a failing water pump? I’m trying to avoid replacing the catalytic converter if something else is actually the root cause.
I know it’s probably all points to the fact that I just need a new catalytic converter but I guess I just want a couple people who know what they’re talking about to confirm it before I spend a bunch of money I’m watching a bunch of videos on how to do it lol.
I have videos of what it sounds like if anybody needs that it just won’t let me post them here.
Any guidance on what should be diagnosed or fixed first would be greatly appreciated.
Thank you,
Bailey
it just won’t let me post them here.
See the topic "READ THIS FIRST - Forum Guide" posted near the top of the main page for information on photos, videos, and much more.
The first 3 codes all refer to cooling system temperature and thermostat problems. If you're lucky the cause is just a bad thermostat.
P0131 indicates a problem with your upstream O2 sensor or its circuitry:
https://www.carparts.com/blog/p0131-o2-sensor-circuit-low-voltage-bank-1-sensor-1/
P0171 indicates a lean condition. (This may be related to the problem being flagged by P0131.):
https://www.obd-codes.com/p0171
If you are going to replace the O2 sensors hopefully you have purchased OEM parts from a trustworthy source. Aftermarket knockoffs have a high probability of not working properly and there are a lot of counterfeits around, particularly at eBay and Amazon.
There is nothing here indicating a water pump problem. Usually those would make noise or weep coolant if they're going bad. Is there play or roughness in the water pump bearing, or is it leaking? (It's also possible for the water pump impeller to come loose or corrode, but that is less common and you would be experiencing overheating problems if that were the case.)
P0420 is usually the catalytic converter but there can be other causes that should be checked out:
https://www.walkerexhaust.com/support/tech-tips/diagnosing-catalytic-converter-p0420-code.html
https://www.carparts.com/blog/p0420-code-catalyst-system-efficiency-below-threshold-bank-1-2-2/
You can use a back pressure gauge to check if the converter is clogged.
Since you have codes there should be freeze-frame data. You might want to check for that as well as live data for issues.
test the catalytic converter. https://www.youtube.com/watch?v=qJTmddbOxMkAny guidance on what should be diagnosed or fixed first
