I've got a scanner, now I need help diagnosing

Hello,
So continuing saga of trying to replace the coolant temperature sensor on my truck..
After replacing the sensor and getting everything together it was running hard and stalling out like it was previously.. I pulled codes with a cheap scanner and they came back with a cylinder misfire and coolant temp sensor low voltage issue..the community told me I needed a better scanner to get more accurate diagnostics..
I got an

$379 Autel mx808 S, 2025 US Ver. of MaxiCOM MK808S/ MK808Z, Bidirectional 11OS as MX900 MK900 MK900BT, 3000+ Active Test, 28+ Service, OE All System OBDII Diagnostic Tool, FCA Autoauth

Autel mx808, which provides live data on most if not all sensors..
The pictures I took are enclosed.. but the coolant temp sensor was coming back with an initial temp of ~46C that rose to ~70C.. not sure if that means it is functional.. also a cylinder 4 misfire..
I am hoping that someone can guide me through diagnosing the truck and figuring out what the issue is.
Thank you for your time.

 

First of all change your units to standard intead of metric, click the gear icon at the top of the screen, go to unit and select inperial.
If you want to change individual units while looking at data click the down arrow next to the data pid you want to change and click the scale icon.

 

I mean, personally I don't have an issue reading centigrade, but thank you for the advice.

 

For those of us that can't do conversions in our head

 

My first guess, knowing NOTHING about anything is that your two issues are probably unrelated. A scan tool is a great diagnostic asset, but it's only part of the equation (and yes, I know, this means spending more money - it's not necessary, but it does help. A lot!). The other part is service information. I use AllData myself, but you can use Mitchells and a couple of others. Most have a 'DIY' option where you can subscribe to individual vehicles for a set fee. I think I pay around $70/vehicle/5 years access at AllData. There you can look up all the specs on the part, review locations for hard-to-find items (esp. connectors), access schematics, and a LOT more

That aside, the easiest way is to let the vehicle sit for 24 hours and then hook up the scan tool. It should read at/near ambient temp (in Fahrenheit or Celsius! ) and then get the truck up to operating temperature where it should read just a bit below boiling. My truck is usually around 195-197 in normal driving. Remember that a circuit high/low code doesn't mean the sensor is borked; there could be a wiring issue between the sensor and the ECU. Having access to the schematic will make this a lot easier as you can go right to the ECU and verify wiring integrity, and then work out from there.

The 304 code could be a bad plug, coil, or fuel injector. Pick one of the two issues and tackle it, then move on to the other.

 

Im going to suspect a common ground / common main connector thats bad if everything has been replaced and those codes keep getting thrown.

 

I've never messed with truck's wiring harness.. is this something difficult to repair? I have experience in electrical work..mostly computer hardware but some home wiring as well, have a multimeter, etc.

 

If you understand basic electrical theory, it's not difficult at all, but you will need the schematics and ground locations. A corroded ground is an excellent candidate for the culprit in normal circumstances, but given that you're getting an 'input low' error vice an 'input high', I'm more inclined to think short circuit vice open circuit.

 

Well, you're in a country that does not use centigrade and you're asking for advice. Wouldn't it be helpful to ask the question in units your audience can understand? Maybe not, since you haven't responded to Dm93's request...

 

46C is 115F and 70C is 158F

 

Not to get too pedantic, but scientists and engineers in the US definitely use C.

 

Yeah, and once again, your audience on this forum is not scientists or engineers. So I guess you deliberately wanted to create an issue?

 

If the engine has sat overnight the coolant temp should read within about 5 degrees of ambient temp, if it doesn't there's a problem.
Operating temp should be 180-200.

 

please display the temperature in kelvins. When you disconnected your battery did you put the terminals back on tight

 

Really? If it's such a challenge to do simple arithmetic, why not just ignore the thread and not add a bunch of useless chaff when other folks are actually trying to help.

 

I didn't mean to start a war about which measurement system is better

 

Hmm... I'd check to see if you have the appropriate amount of coolant, if not maybe you have air in the system and that's what your sensor is picking up. But the bigger question is, where is the coolant going and why do I have a misfire on cylinder 4. Maybe a head gasket is blown burning the coolant in that cylinder, I'd pull that spark plug out and check to see if that cylinder looks clean or wet. An easy check is to see if you have a milky residue on the oil cap or the radiator cap, a mixture of oil, coolant, and exhaust gases is a good indication of coolant mixing with the oil. I hope this isn't your issue, but I figure I'd give my 2 cents, hopefully, it helps.

 

Sooo.. the weather finally got a little better and was able to get some time in this afternoon. I cleared the codes last time, hooked up the scanner and checked the coolant temperature sensor which came back within 1.5F of the ambient temp.. turned the truck on and watched the temp go up in real time.. planned to do work so didn't run it too long.. pulled codes and only 4th cylinder misfire came back.. no coolant sensor low voltage.. checked the oil and coolant.. looked normal.. pulled the 4th coil and it was soaking in oil!
I also noticed there is oil around the edges of the valve cover.. do I just need to replace the inner and outer valve cover gaskets, spark plugs, and soaked coils??

 

Thats the source of your misfire, replace the coil the spark plugs and spark plug tube seals and valve cover gasket.

 

I assume I should/need to drain the oil first?