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1997 Jeep Grand Cherokee Base 4dr Laredo

1997 Jeep Grand Cherokee
Trim Info:
Rear Wheel Drive, 4 Door, Special Purpose Vehicles
16 mpg city / 21 mpg hwy
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January 6, 2013, 4:17 pm

Amber M

Question: Can a bad coolant temperature sensor cause a po420 code?

I have a 98 Jeep Grand Cherokee, and the Check Engine light came on today. I took it the the Advance for one of the code test. They just told me it was a po420 so i would need a new catalytic converter.
After doing research of my own I found that a bad coolant temperature sensor can also cause that code.

Since my coolant temperature sensor is bad would that be the reason for the po420 code? Or do i really need a new catalytic converter?

January 12, 2013, 9:20 am

Ron W
Expert Mechanic

Here is a link to information about that code.

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

If the temp sensor is bad, the vehicle may not be running at operating temp when the OBD Cat and O2 sensors monitors run so an incorrect code could be set.

It is not very likely, and your cat is probably dead, but since you need a sensor anyway, change the sensor, clear the codes and see if the code resets. If it does, the cat is the most likely failure. If it doesn't, you just saved $500.

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