Just got warning p0118 after doing a bunch of work.

I found threads on p0117 but that is for the same code but "low".

Do I just need to replace the sensor by the thermostat?

 

Just found this

The engine coolant temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The powertrain control module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit.

When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P0117 sets.

If the PCM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.


Looks like its all points to the ect, I will replace that.

 

Do you know what the engine temperature actually is when this occurs? One of my other trucks says engine too cool when it is at 195. Really crazy. If you knew waht temp was it may save changing a part that may not be bad. At least you would know for sure first.

 

The gauge in the truck is going on randomly and the temp is right where it is supposed to be.

I know I connected it back correctly but I will have to pull the alternator and check it out I guess.

 

I just changed the sensor and I am still getting the code.

My temp gauge will work for a few minutes when you first start the truck and then drops down to nothing.

Regardless I am still getting the p0118 code, any ideas?

 

Looking at schematic, the sensor grounds itself. It goes through two connectors C127 and C133 and then directly to the gauge. Has to be a badd connection at one of the connectors, at the gauge, or the gauge itself. The sensor that provides input to PCM is not self grounded and connects to A4 and A16. Two sensors, two temp inputs. Gauge is separate from PCM which is where code is coming from.....seems like the problem is illogical.

The gauge and the MIL do not show to be related. One should not cause the other. I'll keep looking.....

 

Does the 99 still have two temp sensors? Thought that changed for 98?

 

It just seems weird they are some what related and both went out at the same time.
The other thing to remember is that the temp gauge works when the truck first comes on so its not a bad connection.


Thanks for helping

 

Only one I saw was just to the passenger side of the thermostat, that is what I replaced.

 

Two wire connector?

I think resistance goes down, as temp goes up. Follow the harness for the temp sensor around, see where it goes, and if you have any shorts anywhere.