Dreaded Misfire P0300

[DankjeeP]

I have 134 miles on the clock, and have been getting misfire code since day one. Taking it in to dealer on Monday.

Sponsored

 

[Discount Dave]

what did you buy and whats build date?

 

[ShadowsPapa]

P0300 is the multiple cylinder misfire. What year is your truck?
There are multiple TSBs (Technical Service Bulletins) for the issue.
Apparently there's one for 2021 3.6 that instructs the tech to replace the spark plugs. That's what they did on my wife's 2021 Grand Cherokee and the misfire went away.
Not sure what vehicles it applies to so can't say if it's Grand Cherokee only or applies to the JT as well. In any case hers has been fine since they did that.
Would love to know the detail - if it's ignition related or otherwise. In the Grand Cherokee case my tools said "ignition misfire".

 

[DankjeeP]

P0300 is the multiple cylinder misfire. What year is your truck?
There are multiple TSBs (Technical Service Bulletins) for the issue.
Apparently there's one for 2021 3.6 that instructs the tech to replace the spark plugs. That's what they did on my wife's 2021 Grand Cherokee and the misfire went away.
Not sure what vehicles it applies to so can't say if it's Grand Cherokee only or applies to the JT as well. In any case hers has been fine since they did that.
Would love to know the detail - if it's ignition related or otherwise. In the Grand Cherokee case my tools said "ignition misfire".

It is a '21 JTR. Just picked it up on 1-22. Seemed sluggish getting on the freeway as I was leaving the dealer, but I didn't think to check the CEL as it was fine the rest of the way home. (1 hour freeway) Took out for a drive next day and noticed same going up a hill from a stop. CEL flashed several times. Got home and read P0300. Drove to office yesterday and noticed it again getting on freeway. Seems fine driving around town, just under more throttle (TPS?) Anyway, hopefully it is resolved on Monday. Would hate to have a lemon

 

[DankjeeP]

what did you buy and whats build date?

Rubicon. Where do I find the build date?

 

[Mr._Bill]

Rubicon. Where do I find the build date?

It's on a sticker in the driver doorway. Upper left is month and year of completion, lower right is month, day, and hour assembly was started.

 

[ShadowsPapa]

Month and year upper left in this photo, MDH is month, day and hour, in lower right in this photo. You have to turn your head sideways, or lay the truck on its side - your choice - to see the sticker right-side-up.

 

[DankjeeP]

Month and year upper left in this photo, MDH is month, day and hour, in lower right in this photo. You have to turn your head sideways, or lay the truck on its side - your choice - to see the sticker right-side-up.

Built 12-20
MDH 122915

I opted to NOT lay the truck on it's side :0

 

[JeepCares]

I have 134 miles on the clock, and have been getting misfire code since day one. Taking it in to dealer on Monday.

How did your dealer appointment go, DankjeeP? Have your concerns been resolved? If not, send us a private message so we can dig in further.

Kate
Jeep Cares

 

[DankjeeP]

How did your dealer appointment go, DankjeeP? Have your concerns been resolved? If not, send us a private message so we can dig in further.

Kate
Jeep Cares

The appointment is on 2-1. I'll be sure to post up the results after. Thanks for checking.

 

[Knolow]

I am having same issues. From what I understand it’s actually the valve cover gasket seal that’s leaking oil onto the O2 sensor Bank 1. Tell your dealer this, changing spark plugs will not fix this.

 

[ShadowsPapa]

I am having same issues. From what I understand it’s actually the valve cover gasket seal that’s leaking oil onto the O2 sensor Bank 1. Tell your dealer this, changing spark plugs will not fix this.

Sorry, You can't say "you have a miss, this is what it will be" - that won't fly because it may be something totally different.
The dealer tech will know if it's ignition or other when they do their scanning. The detailed report will let them know.
In our case, the report I ran showed ignition issue. You won't see that as an owner without using a tool to get that detail - the dealer will.
If it's sensor related, they'll SEE it, and the report will tell them.
Where did you get the idea that a misfire is always going to be oil on the O2 sensor? Changing spark plugs won't fix it? Really? IT sure did in our case - but then, I won't tell people that it will fix EVERY misfire just like you can't say that it won't fix it and it's always going to be oil on the O2 sensors.

The cause varies - it's not the same cause for every single vehicle with a misfire.
Yours may be an oil leak, it may be something else for the next person.
So really - telling people to tell their dealer "don't change spark plugs, it won't fix it!" ?

The dealership will know if it's O2 sensor related or it's ignition related because they'll see this like I did - I ran tests, several, over time, and caught it in the act.

First Service Freeze Frame:
___________________
Fault code: P0303
PCM Mileage since MIL On: 0.00 miles
PCM Odometer: 950.27 miles
Open Loop - Bank 1: No
Closed Loop - Bank 1: Yes
Open Loop due to Driving Conditions - Bank 1: No
Open Loop with DTC - Bank 1: No
Closed Loop with DTC - Bank 1: No
Open Loop - Bank 2: No
Closed Loop - Bank 2: No
Open Loop due to Driving Conditions - Bank 2: No
Open Loop with DTC - Bank 2: No
Closed Loop with DTC - Bank 2: No
Engine load: 30.20 %
Freeze Frame Engine Coolant Temp: 66.00 Deg.C
Intake Air Temperature: 215.00 Deg.C
Ambient Air Temperature: 12.00 Deg.C
Short Term Fuel Trim - Bank 1: 12.49 %
Long Term Fuel Trim - Bank 1: -3.13 %
Short Term Fuel Trim - Bank 2: 9.37 %
Long Term Fuel Trim - Bank 2: -7.04 %
MAP Voltage: 1.96 V
MAP: 46 kPa
Atmospheric pressure: 97 kPa
Engine RPM: 875.00 rpm
Vehicle speed: 0 MPH
Throttle Position Sensor 1 Percent: 12.94 %
Battery voltage: 14.58 V
Fuel level: 95.69 %
Purge Solenoid Current: 0.00 mA
Purge Duty Cycle: 0.00 %
Idle Air Control (IAC) Current: 0.00 mA
Idle Air Control (IAC) Duty Cycle: 0.00 %
EGR Flow: 0.00 g/s
Current Adaptive Cell ID: 24
Spark advance: -2.00 Deg
AC Clutch: Disengaged
EGR Gassed Flowing: No
Power Steering High Pressure: No
AC Switch: Off
PRNDL in Gear: No
Brake switch: Pressed
Low Ethanol PWR Enrich Flag: No
Low Ethanol Therm Management Flag: No
Ethanol Gas For Sure: No
Ethanol Mode: No
Ethanol - 0% Blend Direction: No
Ethanol - 85% Blend Direction: No
Ethanol - Open Loop Fuelling: No
Ethanol Fine Tune Complete Previous: No
Ethanol Fuel Volume Changed: No
Ethanol Low Fuel: No
Ethanol Trigger On Fuel Volume Fault: No
Ethanol Trigger During Learn: No
Ethanol Learn: Disabled
Ethanol Course Update Ready to Learn: No
Ethanol Course Update: Not completed
Ethanol Fine Tune: Not completed
Actual Torque: 0.84 Nm
Potential Torque: 78.16 Nm
Target throttle position: 2.56 V
Electronic Throttle Control (ETC) Motor Directional Duty Cycle: -20.67 %DC
Electronic Throttle Control (ETC) Motor Duty Cycle: 20.67 %DC
Throttle position sensor 1: 2.58 V
Throttle position sensor 2: 17.42 V
Accelerator pedal sensor 10.44 V
Accelerator pedal sensor 20.22 V
Accelerator pedal position: 0.00 %
Brake switch 1: Released
Brake switch 2: Released
H-Bridge Circuit: Enabled
Ignition Run/Start Switch: On
Throttle Flow Adaptive: 0.13 g/s
Throttle Flow Multiplicative Adaptive: 2.00
PHI Adaptation Value: 0.00
Calculated MAP: 46.59 kPa
Ethanol Percent: 0.00 %
Turbo Boost Timer: 0.00 ms
Throttle Inlet Pressure: 0.00 kPa
Throttle Inlet Pressure Voltage: 320.34 V
Turbo Airport Mass Flow: 3.45 g/s
Turbo PRatio: 1.00
Turbo Torque Count: 0
Turbo Speed: 65535 rpm
Turbo Wastegate Duty Cycle: 200.01 %DC
Time since Run/Start: 45 sec
___________________

 

[Knolow]

Sorry, You can't say "you have a miss, this is what it will be" - that won't fly because it may be something totally different.
The dealer tech will know if it's ignition or other when they do their scanning. The detailed report will let them know.
In our case, the report I ran showed ignition issue. You won't see that as an owner without using a tool to get that detail - the dealer will.
If it's sensor related, they'll SEE it, and the report will tell them.
Where did you get the idea that a misfire is always going to be oil on the O2 sensor? Changing spark plugs won't fix it? Really? IT sure did in our case - but then, I won't tell people that it will fix EVERY misfire just like you can't say that it won't fix it and it's always going to be oil on the O2 sensors.

The cause varies - it's not the same cause for every single vehicle with a misfire.
Yours may be an oil leak, it may be something else for the next person.
So really - telling people to tell their dealer "don't change spark plugs, it won't fix it!" ?

The dealership will know if it's O2 sensor related or it's ignition related because they'll see this like I did - I ran tests, several, over time, and caught it in the act.

First Service Freeze Frame:
___________________
Fault code: P0303
PCM Mileage since MIL On: 0.00 miles
PCM Odometer: 950.27 miles
Open Loop - Bank 1: No
Closed Loop - Bank 1: Yes
Open Loop due to Driving Conditions - Bank 1: No
Open Loop with DTC - Bank 1: No
Closed Loop with DTC - Bank 1: No
Open Loop - Bank 2: No
Closed Loop - Bank 2: No
Open Loop due to Driving Conditions - Bank 2: No
Open Loop with DTC - Bank 2: No
Closed Loop with DTC - Bank 2: No
Engine load: 30.20 %
Freeze Frame Engine Coolant Temp: 66.00 Deg.C
Intake Air Temperature: 215.00 Deg.C
Ambient Air Temperature: 12.00 Deg.C
Short Term Fuel Trim - Bank 1: 12.49 %
Long Term Fuel Trim - Bank 1: -3.13 %
Short Term Fuel Trim - Bank 2: 9.37 %
Long Term Fuel Trim - Bank 2: -7.04 %
MAP Voltage: 1.96 V
MAP: 46 kPa
Atmospheric pressure: 97 kPa
Engine RPM: 875.00 rpm
Vehicle speed: 0 MPH
Throttle Position Sensor 1 Percent: 12.94 %
Battery voltage: 14.58 V
Fuel level: 95.69 %
Purge Solenoid Current: 0.00 mA
Purge Duty Cycle: 0.00 %
Idle Air Control (IAC) Current: 0.00 mA
Idle Air Control (IAC) Duty Cycle: 0.00 %
EGR Flow: 0.00 g/s
Current Adaptive Cell ID: 24
Spark advance: -2.00 Deg
AC Clutch: Disengaged
EGR Gassed Flowing: No
Power Steering High Pressure: No
AC Switch: Off
PRNDL in Gear: No
Brake switch: Pressed
Low Ethanol PWR Enrich Flag: No
Low Ethanol Therm Management Flag: No
Ethanol Gas For Sure: No
Ethanol Mode: No
Ethanol - 0% Blend Direction: No
Ethanol - 85% Blend Direction: No
Ethanol - Open Loop Fuelling: No
Ethanol Fine Tune Complete Previous: No
Ethanol Fuel Volume Changed: No
Ethanol Low Fuel: No
Ethanol Trigger On Fuel Volume Fault: No
Ethanol Trigger During Learn: No
Ethanol Learn: Disabled
Ethanol Course Update Ready to Learn: No
Ethanol Course Update: Not completed
Ethanol Fine Tune: Not completed
Actual Torque: 0.84 Nm
Potential Torque: 78.16 Nm
Target throttle position: 2.56 V
Electronic Throttle Control (ETC) Motor Directional Duty Cycle: -20.67 %DC
Electronic Throttle Control (ETC) Motor Duty Cycle: 20.67 %DC
Throttle position sensor 1: 2.58 V
Throttle position sensor 2: 17.42 V
Accelerator pedal sensor 10.44 V
Accelerator pedal sensor 20.22 V
Accelerator pedal position: 0.00 %
Brake switch 1: Released
Brake switch 2: Released
H-Bridge Circuit: Enabled
Ignition Run/Start Switch: On
Throttle Flow Adaptive: 0.13 g/s
Throttle Flow Multiplicative Adaptive: 2.00
PHI Adaptation Value: 0.00
Calculated MAP: 46.59 kPa
Ethanol Percent: 0.00 %
Turbo Boost Timer: 0.00 ms
Throttle Inlet Pressure: 0.00 kPa
Throttle Inlet Pressure Voltage: 320.34 V
Turbo Airport Mass Flow: 3.45 g/s
Turbo PRatio: 1.00
Turbo Torque Count: 0
Turbo Speed: 65535 rpm
Turbo Wastegate Duty Cycle: 200.01 %DC
Time since Run/Start: 45 sec
___________________

thank you for taking the time to clarify this. You seem to have a tone in your response, I am highlighting this as I am not trying to mislead anyone. People should know when they read something to take it light heartedly especially that I am simply applying my 2 cents to a public forum not a science journal. I had similar issues changed my spark plugs and it came back 9 months later. I got my Jeep when they were released and have along time dealing with this issue back early 2019. With all this said you do have a point not everyfix applies blanket style so for the original intent I’m just trying to help as my dealer blamed sparks let me go thinking it was fixed but sure enough I kept dealing with loss of auto start/stop then misfires again.

 

[ShadowsPapa]

thank you for taking the time to clarify this. You seem to have a tone in your response, I am highlighting this as I am not trying to mislead anyone. People should know when they read something to take it light heartedly especially that I am simply applying my 2 cents to a public forum not a science journal. I had similar issues changed my spark plugs and it came back 9 months later. I got my Jeep when they were released and have along time dealing with this issue back early 2019. With all this said you do have a point not everyfix applies blanket style so for the original intent I’m just trying to help as my dealer blamed sparks let me go thinking it was fixed but sure enough I kept dealing with loss of auto start/stop then misfires again.

You may have had a dealer that's, well, less than willing to actually investigate and troubleshoot. Not that it's easier in the last 30 years, it's not, but still......... they have tools.
The spark plug TSB I don't have a copy of, I need to ask the dealer for it, but from my understanding it's something FCA tells them is a possible cause of ignition-related misfires. Normally the system will be able to differentiate the cause of the misfire - so it should state ignition, whatever.
I have to wonder if you aren't in the club with others who have mystery multiple misfires and they end up replacing everything but the rear axle seals or front u-joints to try to solve it, to no avail. Some get a PCM flash - there, that should fix it - and luckily for SOME it does, for others - nope, it's BAAAACK! Ugh. So they go back in and rockers are replaced, phasers are replaced, shift lever is replaced (kiddding, but you see my point - let's throw parts at it and see if anything helps)
I'm thankful my JT has not yet had any misfires - at least nothing you could feel, hear or otherwise sense, and the MIL has never even flickered (or is it CEL? MIL is Malfunction Indicator Light, the term Jeep used in the 90s, but it appears to be Check Engine Light....... odd because MIL is more fitting when it comes on and it's not actually an engine issue) Anyway, my JT has been fine in that way.
Then along comes my wife's Jeep - a 2021 Grand Cherokee. I've read many of the "misfire" related posts here, done a lot of digging and research and when she reported her Jeep was jumpy and I went out and started it and felt it, I had that "oh, sxxx" feeling........
I ran diagnostics, drove it, printed the report and went to the dealer with it. Of course getting onto the bypass I had to nail it to merge into commute traffic and suddenly instead of the thing bucking, it smoothed out and was fine the final 12 miles or so. Damn.
Like taking a kid to the doctor.
They said they tried and tried and finally did get it to misfire a couple of times - but didn't get it to keep doing it. They dug through every FCA TSB and communication they had, the only thing that fit close at all was the spark plug TSB. They performed that (I don't envy them, taking the intake off and other fun stuff to get to spark plugs I can change i 10 minutes in my cars and my other Jeep) It's been fine since.
O2 sensors - the "MIL" or "CEL" came on with my other Jeep - I plugged in and ran Torque on it and it indicated bank 2 sensor 1 O2 sensor heating circuit troubles. Mine was outside of the TSB issued for that issue so I figured it was real. (certain build dates were supposed to get a PCM flash to cure the false alarm - mine was outside of that build date range)
I figured what the heck, reset the thing- got rid of the code, the CEL went off, and that was like 3 months ago - it's been fine since. So obviously, their TSB dates were wrong and mine should have been included in the PCM flash.

 

[DankjeeP]

Here's to hoping it is as "simple" on my Jeep

Sponsored