2004 Ford Mustang GT serpentine belt diagram

Maintenance/Repairs
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I am not familiar with the term “block test”. The CHT or coolant sensors are tested in a way similar to any other temp sensor. It should have a particular voltage at a particular temp. . A test of this circuit will also require testing the input voltage from the PCM and testing the wires for shorts and opens. Since it is an intermittent problem, it might be difficult. I can give you some values for my '99 4.6 l. but I can’t say if they will be the same for your car. At 68 F, 37 K ohms; at 104 F, 16 K ohm; at 194 F, 2.75 k ohm. The voltage between Vref and sig return should be 4-6 volts with the TP sensor disconnected and the Key on, engine off.

Are you sure the coolant level is correct? Have someone tap on the temp sensors and watch the gauge to see if it changes. Wiggle the temp sensor wires and see if the temp gauge changes. Wiggle the connectors in the temp sensor circuits and see if the temp gauge changes. If you are going into the Fail-safe cooing mode, I believe that a DTC will be set.

Let’s get back to another piece of information. I am almost certain that you have a two-speed fan. It should come on low, and then high as the engine warms up. It should be on high with the AC on. Verify that the fan is working properly.

www.crownvic.net has a lot of knowledge of 4.6L motors. Try also www.flatratetech.com

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Oh, I did finally check the fan and it is two speed. It first came on low when the temperature started climbing to the normal range. When it got to the full normal range the fan kicked in to high so it is good.
A block test, as it was explained to me was simply connecting the car to their computer and starting the engine. Once it reaches normal operating temperature a diagnostics signal is sent to the computer which says perform a self test and return the results. Everything passed with no problems found. They tell me the dealer has a better test that they can run which should isolate the problem and tell me exactly what the computer is seeing that causes it to shut the engine down.

I did as you suggested and got no fluctuation out of the temperature guage but have not had the time to perform the electrical test.

I am going to do a compression test with all of the spark plugs removed to see if there is any differences between cylinders this weekend so I’ll wait until then to do the electrical testing as well.

Thanks for the references I looked through them and found a welth of information.