Coolant Temperature Sensor Emission EFI RPM Ignition Advance

[nissanh]

The TWO wire Coolant sensor is a device to monitor the engine temperature and adjust other parameters to make the engine to run in its optimal performance.

This sensor controls the engine open-loop and close-loop cycle, Ignition Spark advance (happens only in closed-loop). It also controls the fuel injector pulse width (how long the injector is kept open 3 ms or 7 ms etc.,) which directly contributes to the gas mileage.

My 4Runner gas mileage has gone down significantly. It used to do 21 MPG on Highway and now it is down to 16 MPG. City is 10-12 MPG. I have replaced air-to-fuel ratio sensor (denso), cleaned MAF, Fresh spark plugs but no change.

I recently read about this coolant sensor and wanted to replace it as well. Went with OEM Toyota 89422-35010 (Check partsouq.com parts diagram before you order yours)

Also keep a new wire plug handy as it can be brittle and can break (mine didn't, but the tab broke off) 10737-11062

Prior to the replacement, 4runner has a noticeable vibration at idle. I can feel it all over the vehicle body.. it comes and goes every 4 to 5 seconds.

This is a demonstration purposes only:

Start on a cold day (so no need to remove coolant or it is under pressure).
Loosen and pull the upper hose clamp towards the radiator
Remove 6 x 10 mm bolts on timing belt cover

Using a 17 mm ring-wrench loosen the driver side fuel rail bolt (no need to remove it completely)
If necessary loosen the 12 mm bolt holding the fuel rail to the cylinder head.
Loosen and remove the passenger side (right side) fuel rail bolt on by-pass tube. May need some prying to release the 17 mm bolt(CAUTION: MAKE sure you are ready to catch the washer between the by-pass tube and the fuel rail).
ALSO Make sure you are not dropping the 17 mm bolt or the washer into the timing belt chamber!

Use a 19 mm deep socket to remove the coolant sensor. Coolant will NOT come out (keep the radiator cap closed). Keep an eye for the copper washer between the sensor and the cylinder head. Installation is the reverse. Do NOT over tight the sensor.

Things I've noted soon after the fix: The vibration at idle is completely gone! Engine barely vibrates at 670-690 RPM. Video - YouTube
Last picture is the removed sensor

 

[spartacus]

Thanks for the write up. I need to tackle this on mine.

 

[phattyduck]

An OBD-II scanner that can read live data (handheld or Scangauge II, etc.) will let you know if the engine temp values that the ECU is reading from the sensor are reasonable. At cold startup, the value should be the outside temperature (within reason) and once warm should be in the normal range (~190*F for most working 5VZ cooling systems). If that isn't true, the sensor could very well be the issue...

As you know the gauge on the dash is a different sensor (errr... sender) and doesn't give you much actual information.

-Charlie

 

[nissanh]

^^ Exactly. I measured the ohm reading which should be about 2000 to 2500 when cold and should drop to about 300 ohms when hot and I saw those readings in the old sensor, but upon removal I notice the internal of the sensor is not fully seated to the copper housing/protruded section of the sensor. Since the OEM sensor was $35 at partsouq, I went ahead and bought a new unit. I'll post a picture below of the old unit. The black casing which I believe should be a glue that sticks to the copper sensor but was loose and falling off.

 

[brillo_76]

Very interesting.. Thanks for sharing so if the obd temp reading are not close to actual temperature. Then best to very your ecu temperature sensor.

Just wanted to add the Toyota connector part number in case someone wanted to use the original connector
Toyota Part number 90980-11062 Genuine Toyota Housing, Connector F
However, this is just the connector where the OP has a pigtail aftermarket replacement which may be a better option.

Great job nissanh. Glad your rig is running a lot smoother with better MPG.