Throttle Body Sensor Issues

[MOPAR78]

I’ve changed the TB twice, once with an original TB and then with the new one. Oddly when it does that, the water temperature on the dash readout goes flat line. I read that the temperature sensor may cause the TB sensor issue. I changed that and I have a new ECM. I noticed this morning that the errors only appear when the outside temperature is 39* or lower. When it’s 40* or higher, no issues at all. That’s odd. The next thing I’m going to try is to reinstall the thermostat due to the fact that it takes forever to warm up for obvious reasons. I’m hoping that this will work. And yes, I have a fuel sensor to replace, it only reads when the tank is full and fails when it drops a few gallons.

 

[Fast69Mopar]

I’ve changed the TB twice, once with an original TB and then with the new one. Oddly when it does that, the water temperature on the dash readout goes flat line. I read that the temperature sensor may cause the TB sensor issue. I changed that and I have a new ECM. I noticed this morning that the errors only appear when the outside temperature is 39* or lower. When it’s 40* or higher, no issues at all. That’s odd. The next thing I’m going to try is to reinstall the thermostat due to the fact that it takes forever to warm up for obvious reasons. I’m hoping that this will work. And yes, I have a fuel sensor to replace, it only reads when the tank is full and fails when it drops a few gallons.

View attachment 561543View attachment 561544

What year is this truck?

If you look at the wiring diagram you will see that all of the engine sensors run off of a 5V supply from the PCM. There are many engine sensors that receive their 5V supply from the same circuit. What that means is if a sensor fails or is failing it has the potential to take down the 5V circuit. It may not be a direct short to B+ power or a direct short to ground either. A sensor can fail and bring down the voltage just a little or a lot on the 5V supply.

The way that I would diagnose this issue is by looking at the wiring diagram for the throttle body and then following the 5V supply circuit to see what other sensors are on the same circuit. I then start to unplug each sensor one by one while monitoring the 5V supply circuit with my DVOM. If you come across a sensor that changes the voltage on the circuit then you know you have found a sensor that is contributing to the concern.

Continue to disconnect each sensor on the 5V supply circuit to verify that each one does not alter the 5V circuit when connected.

Our engine sensors are a 3-wire setup.

5V
Ground
Return

The PCM supply's the 5V to the sensor on one pin, another pin is grounded and the 3rd pin is the return to the PCM. 5V's goes in to the sensor and through the circuitry of the sensor and it alterns the voltage and then the return circuit carries the sensors voltage back to the PCM. It's a very simple setup and it works very well. Each sensor has a voltage range that it operates inside and the PCM uses the voltages to operate the engine. When a sensor returns the wrong voltage or something outside of that range the PCM sees that and sets a corresponding DTC and turns on the MIL.

 

[MOPAR78]

What year is this truck?

If you look at the wiring diagram you will see that all of the engine sensors run off of a 5V supply from the PCM. There are many engine sensors that receive their 5V supply from the same circuit. What that means is if a sensor fails or is failing it has the potential to take down the 5V circuit. It may not be a direct short to B+ power or a direct short to ground either. A sensor can fail and bring down the voltage just a little or a lot on the 5V supply.

The way that I would diagnose this issue is by looking at the wiring diagram for the throttle body and then following the 5V supply circuit to see what other sensors are on the same circuit. I then start to unplug each sensor one by one while monitoring the 5V supply circuit with my DVOM. If you come across a sensor that changes the voltage on the circuit then you know you have found a sensor that is contributing to the concern.

Continue to disconnect each sensor on the 5V supply circuit to verify that each one does not alter the 5V circuit when connected.

Our engine sensors are a 3-wire setup.

5V
Ground
Return

The PCM supply's the 5V to the sensor on one pin, another pin is grounded and the 3rd pin is the return to the PCM. 5V's goes in to the sensor and through the circuitry of the sensor and it alterns the voltage and then the return circuit carries the sensors voltage back to the PCM. It's a very simple setup and it works very well. Each sensor has a voltage range that it operates inside and the PCM uses the voltages to operate the engine. When a sensor returns the wrong voltage or something outside of that range the PCM sees that and sets a corresponding DTC and turns on the MIL.

Rams is a 2014. Demon LB is a2024. I was a 31 Echo in the Army years ago . I have good knowledge about schematics. Thanks for the advice and information about this. I appreciate it!! Very helpful information!