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Q: Car is in limp mode and making strange sound when beginning to rev.

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Hi. The Jeep's ETC light came on and then it went into limp mode. After shutting the car off for some time, limp mode is gone for a few, and it makes a weird, almost "coughing" sound when revved. It will do this a few times and then go back into limp mode and won't make the sound anymore. I have scanned it and I am getting a P0420 code. Is my throttle body bad, stuck, or what? Is it an O2 sensor issue? I am at a loss here....

My car has 120000 miles.
My car has an automatic transmission.

Hi there:

When the oxygen sensors have a reading that is similar to each other, it is an indication that the catalytic converter is not working as efficiently as it is intended. If the voltage of the downstream oxygen sensor decreases, and begins to fluctuate like the upstream oxygen sensor, it means that the oxygen levels are too high and the Power Control Module will then store the [P0420 trouble code[(https://www.yourmechanic.com/article/p0420-obd-ii-trouble-code-catalyst-system-efficiency-below-threshold-bank-1-by-jamahl-walker). However, faulty O2 sensors or damaged exhaust system components typically won’t trigger the limp mode to be activated; as that’s usually a transmission fault. If you’re hearing a weird noise, it’s likely you have a hole in the exhaust somewhere that is triggering this OBD-II trouble code.

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