Got this off the interweb
The causes for this DTC may include: Check for loose or corroded connectors or terminals, which is often the case
Broken wires or missing insulation may be causing a short directly to ground
The sensor may have failed
A catback exhaust system without EGT provisions installed
It's possible, although not probable, that the computer has failed
Repairs
Raise the vehicle and locate the sensor. Its between the exhaust manifold and the converter or, in the case of a diesel, before the Diesel Particulate Filter (DPF). It looks different from the oxygen sensors in that is just a plug with two wires. A vehicle with a turbo will have the sensor next to the turbo exhaust input. Check the connectors for any abnormality such as corrosion or loose terminals. Follow the pigtail up to its connector and check that one as well. Look for signs of missing insulation or bare wires that may be shorting to ground. Disconnect the upward connector and remove the EGT sensor. Check the resistance with an ohmmeter. Probe both terminals in the connector. A good EGT will have about 150 ohms. If there is very little resistance -- below 50 ohms replace the sensor. Use a hair dryer or heat gun and heat the sensor while you watch the ohmmeter. The resistance should drop as the sensor is heated and rise as it cools. If not, replace it. If all was good to this point, turn the key on and measure the voltage at the engine side of the pigtail. There should be 5 volts at the connector. If not replace the computer.
Read more at:
http://www.obd-codes.com/p0546
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