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Old 01-22-2013, 03:22 PM   #7
Focus Rookie
Join Date: Jan 2013
Fan#: 108520
Location: Portland, OR
What I Drive: 2003 Blue ZX3

Posts: 19
FF Reputation: 1 rycodge Good Standing Member
Buy-Sell-Trade Rating: (0)
I'm getting stumped once again.

I replaced my thermostat and it appears my original thermostat was working correctly. Car exhibited the same symptoms (low temp readings from the CHT sensor).

Next, I thought, "I must have a bad CHT sensor". I buy a replacement and go through all of the fun involved removing the alternator and remove the old sensor. I decide to test the old and new sensor.

I tested each CHT sensor's resistance readings in
1) a cold cup of water
2) a warm cup of water (~100 degrees F)
3) an almost boiling cup of water (close to 190 degrees F).

Readings from both CHT sensors responded well and were nearly identical. Each reading was within 100 ohms which is expected. I'm about to put my alternator back on and return my car to a running condition tonight. I am not expecting any improved results.

I'm going to make sure that I check a few of the grounds for the wiring harnesses. I can't seem to figure out WHY my focus's ECU is telling me that the Engine Temp is only around 100-130 degrees F if my CHT is behaving as expected. The only logical reason would be a voltage drop in the sensor feed?

Any one have any ideas on this one?
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