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Old 12-19-2014
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ECT Sensor and Check Engine Light

My son's 2003 Ranger Edge, 3.0L. AT, exhibits the following symptoms:

1. Temp gauge indicates engine is slow to heat, maxes out at 1/3 gauge scale
2. Check Engine light recently illuminated.
3. Autozone OBD reader reports P0125, P0172, and P0174
4. On initial cold startup, after several minutes, there is an audible "click" and radiator top hose begins to heat up.
5. There is only one wire coming out of the ECT sensor and entering a wire harness 8 inches away. The ECT sensor connector has holes for 2 wires.
6. The engine is a recent (1 month ago) replacement with about 60K miles. He has put several hundred problem-free miles on it since the replacement.
7. Weather has recently turned significantly colder.


My thoughts: Research of the OBD codes points to a coolant temp problem, probably the thermostat, less likely the ECT sensor. Based on the codes and other things I've read online, less likely causes include O2 sensor(s), Mass Airflow Sensor, and others.

I was about to change the thermostat on the guess that it is defective, opening at a lower than desired temperature. Based on the "click" I'm hearing, I'm fairly certain it's not stuck open. I was prepping to replace it with a 192 degree thermostat when I noticed the single wire coming from the ECT Sensor and decided to run this by you guys.

My question for you experts: Does anyone know whether there should be a second wire leading from the ECT Sensor? If not, am I on the right track with the thermostat?

Thanks in advance,

B
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Old 12-19-2014
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Update: Just replaced the thermostat. The old thermostat looked fairly new but was stamped "180F". I replaced it with a new 192F version. Permatex needs 24 hrs to dry so I won't know anything until this time tomorrow. Any predictions?
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Old 12-19-2014
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Yes, thermostat was incorrect, 192degF is the proper thermostat.

All fuel injected engines have an ECT(engine coolant temp) sensor, and ECT sender.
ECT sender is for the dash board gauge and has only 1 wire
ECT sensor is for the computer(PCM) it has 2 wires.

P0125 could be caused by the incorrect t-stat and the colder weather.

P0172 - Rich on Bank 1 (passenger side)
P0174 - Lean on Bank 2 (drivers side)

These do not make sense, recheck those numbers
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Old 12-23-2014
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Thanks Ron. You were correct re the thermostat.

As noted above, I replaced the old 180 degree thermostat with a new 192 degree thermostat. It corrected all symptoms. Engine now heats up very quickly (less than 5 minutes on the highway) and stabilizes at just below mid-scale. After about 50 miles of driving and 5-10 cold start cycles, the check engine light cleared.

I'm still puzzled about the P172 and P174 error codes. Could they be due to less-than-optimal combustion because the engine temp was 12 degrees lower than it should be?

Last edited by Bobby62; 12-23-2014 at 04:37 PM.
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Old 12-23-2014
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P0172 (rich on bank 1) means the computer has reduce the fuel injector's open time(pulse width) on that Bank as much as it can and the O2 sensor is still reporting too little Oxygen.
O2 sensors can only "see" oxygen, not fuel.

P0174 (lean on Bank 2) means computer has opened injectors as long as it can and O2 sensor is still reporting too much oxygen

This could be dirty MAF sensor, Mass Air Flow sensor sets the baseline the computer uses to calculate how much fuel to add to the air, if MAF is dirty it usually reports less air so baseline is skewed for less fuel than is actually needed so you get rich.

When a cylinder misfires it doesn't burn all the oxygen in the cylinder, this oxygen is dumped into the exhaust and O2 sees it as too much oxygen, lean.

A rich mix can foul a spark plug, coats it with carbon, this can cause random misfires.

So you get 172 and 174

Just guessing
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