Thermostat Replacement and DTC Codes P0113 and P0420 | Ford Explorer Forums - Serious Explorations

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Thermostat Replacement and DTC Codes P0113 and P0420


August 29, 2001
Reaction score
City, State
rockland, ny
Year, Model & Trim Level
1996 XLT
I replaced the thermostat in my 96 explorer and after a 1 mile drive the Check Engine Light came on. Auto Zone pulled the DTC codes, P0113 and P0420.

Wondering if I installed the thermostat the wrong way to cause the codes. Does someone have a picture how the thermostat should be inserted?

P0113 - Intake Air Temperature (IAT) Circuit High Input
P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

I don't see anything having to do with coolant issues -- did you hook everything back up right?


I installed my thermostat backwards one time on my Mounty. It ended up running ice cold no matter how long I drove it. You should install the thermostat with the spring side facing the engine block. I'd check the wiring to the IAT sensor first.

On my 5.0, the IAT is built into the MAF housing. If yours is the same way, inspect the wires on the inside for damage.

I'd repair the IAT problem first, and then clear the codes. If the P0420 code comes back by itself, I'd say that it's another unrelated issue.

Disconnect your battery to reset the codes and see if they come back if they don't your good if not you have a problem somewheres.
P0420 is either your 02 sensor on the passanger (behind the cat) bad or your cat going bad.