Question: I have a 2001 Jeep Grand Cherokee with the 4.0-liter six-cylinder and about 120,000 miles. I keep getting a catalytic converter code P0420. I heard there may be a way to fix it by spacing the O2 sensor away from the cat and changing the reading.

Answer: That's a new one for me, and I cannot see it having any effect on preventing a P0420 DTC, but it is illegal. P0420 indicates the catalytic converter has lost its efficiency in reducing harmful emissions. Although there are possible causes other than a failed cat causing the code, the majority of the time, converter replacement is the one and only fix. The powertrain control module evaluates the primary O2 sensor reading (before the cat) and the secondary sensor reading (downstream) to determine if the converter is doing its job. When the two readings get close to being the same, the PCM stores DTC P0420 and turns on the check engine light. I know catalytic converters can be expensive -- some are in the $1500 range. I've seen folks just keep on driving, and sell the truck when their state inspection comes up for renewal. There's no other way around replacement.


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