Yo Need Help with Equinox - Engine Underboost and P0420 Codes

Chevy Error Codes Forum
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I’ve got a Chevy Equinox I’m trying to fix. The vehicle is throwing engine underboost and P0420 codes. I followed the DTC (Diagnostic Trouble Code) and replaced the turbo, but even after that, both codes are still there. Both O2 sensors are fine, and their graphs look good. New turbo is installed, and there are no leaks in the pressurization system. Anyone have any idea what else could be causing this? Any help is appreciated!

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What year is the Equinox?

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Teal said:
What year is the Equinox?

It’s a 2024.

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If you’ve already replaced the turbo and confirmed no leaks, it might be worth checking the catalytic converter. P0420 is typically related to the cat, and if it’s clogged or damaged, it could be affecting both codes. Have you checked the backpressure in the exhaust?

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@Leith
I haven’t checked the backpressure yet, but that’s a good point. I’ll take a look at the catalytic converter and see if that could be causing the issue.

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For the underboost, it could also be a problem with the wastegate actuator. Sometimes they get stuck or aren’t adjusted properly, which would still throw underboost codes even with a new turbo.

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Drew said:
For the underboost, it could also be a problem with the wastegate actuator. Sometimes they get stuck or aren’t adjusted properly, which would still throw underboost codes even with a new turbo.

I didn’t check the wastegate. I’ll check that next and see if there’s any issue there. Thanks!

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You mentioned the O2 sensors are fine, but did you check the wiring? Sometimes the sensors themselves are good, but the wiring can have issues that throw the same codes.

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Kim said:
You mentioned the O2 sensors are fine, but did you check the wiring? Sometimes the sensors themselves are good, but the wiring can have issues that throw the same codes.

Good question, I’ll double-check the wiring for the O2 sensors. I haven’t inspected that yet.

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Another thing to check is the boost control solenoid. If it’s malfunctioning, it might not be regulating the boost correctly, causing the underboost code.

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Jai said:
Another thing to check is the boost control solenoid. If it’s malfunctioning, it might not be regulating the boost correctly, causing the underboost code.

I didn’t think of that. I’ll check the boost control solenoid next.