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Chris (aka-Moose)
Chris (aka-Moose), Auto Technician
Category: Toyota
Satisfied Customers: 868
Experience:  16 years of experience
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I have a P0118 fault code on my 2006 tundra, but i have

Customer Question

i have a P0118 fault code on my 2006 tundra, but i have checked the senor and the reading is correct also with the senor disconnected the reading is -40 and jumped-out 284 degf I do not have a check engine light the only indication there was an issue the temp gauge is showing a low temperature
JA: Does the light stay on, or does it blink?
Customer: which light... the check engine did not come on
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I have checked the temp reading in the ECM with the sensor connector disconnected and jumped out and the reading are good but the temp gauge is incorrect
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Toyota Mechanic about your situation and then connect you two.
Submitted: 8 months ago.
Category: Toyota
Expert:  david craig replied 8 months ago.

Hi I'm Dave,here
P0118 - Engine Coolant Temperature Circuit High Input
Possible causes - Low engine coolant level
- Engine Coolant Temperature (ECT) sensor harness is open or shorted
- Engine Coolant Temperature (ECT) sensor electrical circuit poor connection
- Faulty Engine Coolant Temperature (ECT) sensor
- Faulty engine coolant thermostat P0118 Description The Engine Coolant Temperature (ECT) sensor is used to detect the engine coolant temperature. The sensor modifies a voltage signal from the Engine Control Module. The modified signal returns to the ECM as the engine coolant temperature input. The sensor uses a thermistor which is sensitive to the change in temperature.

Customer: replied 8 months ago.
Dave, I have checked these possible causes.....I am puzzled by this .....when I connect my OBD-II scanner the temp reading value in the ECM is correct but the temp gauge is reading a very low temp even when the engine is at 180 degf
Expert:  david craig replied 8 months ago.

ok, let me check. there might be 2 sensors. 1 for the gauge and i for the computer.

Expert:  david craig replied 8 months ago.

4.0 or 4.7?

Customer: replied 8 months ago.
4.7
Expert:  david craig replied 8 months ago.

ok it only has 1 sensor. have you tried replacing the thermostat?

Customer: replied 8 months ago.
I replaced the thermostat
Customer: replied 8 months ago.
according to my ODB scanner the engine temp is actually 184 degf when running
Expert:  david craig replied 8 months ago.

what degree thermostat did you put in.

Customer: replied 8 months ago.
180
Customer: replied 8 months ago.
that was OEM part
Expert:  david craig replied 8 months ago.

what temp reading is the gauge showing at the middle hash mark?

Customer: replied 8 months ago.
no it is showing at 5 o'clock ...normally it would show at 3 o'clock thats how I noticed something was wrong
Expert:  david craig replied 8 months ago.

but is there is degree mark at 3 o'clock? like 180 or 210?

Customer: replied 8 months ago.
no is just "C" at the bottom and "H" at top
Expert:  david craig replied 8 months ago.

ok. well if it aint too much of a pain. put some heat on the sensor and see what the gauge does.

Expert:  david craig replied 8 months ago.

and if you have a digital temp gun, compare the temp where the sensor go into the engine and the gauge or the scan tool

Customer: replied 8 months ago.
i heated some water to 180 degf and placed the sensor in water the ECM reading is 179.1 but the gauge is between 5 & 6 o'clock
Expert:  david craig replied 8 months ago.

lets do a wiggle test of the wiring to the sensor and see if the gauge jumps...also make sure the sensors connector has a good ground

Customer: replied 8 months ago.
done that I have wiggled every wire and harness under the hood
Expert:  david craig replied 8 months ago.

how about the ground for the connector? it should read no more than 0.2 ohms

Customer: replied 8 months ago.
connector has good ground .1 ohms and the supply is 5.1 VDC
Expert:  david craig replied 8 months ago.

in my opinion it has to be the instrument cluster then. you can also try a 195 degree thermostat to bring it to 3 o'clock

Customer: replied 8 months ago.
does the temp gauge get its signal from the ECM or directly from the sensor
Expert:  david craig replied 8 months ago.

directly from the ecm

Expert:  david craig replied 8 months ago.

Here is what the circuit does. The (PCM) provides a 5 volt reference and a ground to the sensor. The PCM monitors voltage drop to determine coolant temperature. If the ECT reads less than freezing temp when engine has been running for more than a few minutes, the PCM determines a circuit fault and sets this code. Or if the PCM determines the sensor resistance is out of specs, this code is set.

Customer: replied 8 months ago.
I sure it is VDC do you know the voltage range of the gauge.
As a side note I am surprised that the PCM sees this fault and does not turn on the check engine light
Expert:  david craig replied 8 months ago.

dont know the voltage range my friend. and its only supposed to set a code. now if there was a fault with the ect and thermostat operation it would turn on the light

Customer: replied 8 months ago.
39;If the ECT reads less than freezing temp when engine has been running for more than a few minutes, the PCM determines a circuit fault and sets this code", but the PCM is not seeing a freezing temp according to my scanner....when the engine starts I have a temp of 89 degf today.
Expert:  david craig replied 8 months ago.

im thinking it means less than what it should read

Customer: replied 8 months ago.
89 is well above freezing if thats what triggers the fault......I believe I read that the fault is generated when the voltage is below .15 and above 4.91 for some time on start up......which would not be the case if the PCM has a value of 89......it makes no since to have the P0118 fault code
Expert:  david craig replied 8 months ago.

looks like you're going to half to pull the instrument cluster and do a continuity test between the gauge and the ecm. point to point then to ground