Hello everyone!
While I haven't upgraded my TJ to a JK just yet, I have been working on my nieces jeep(2011 JK 2 door 42rle) She originally had a p1776 code. As a first step, I changed the fluid and filter and the code cleared for a while. She recently has been complaining about a loud noise recently and a bunch of codes popped up.
P0306
P0721
P1776
P1790
The 306 cylinder 6 misfire is probably unrelated. When I changed the oil and filter
The 0721 and 1776 I'm wondering if there is a bad connection or ground somewhere causing the issue. Has anyone had the same issues, or knows common grounds or connections to check and clean?

 

Could be seen as obvious, but I presume you are talking about having changed transmission fluid and filter given the related codes are transmission related. Are you certain that you got the proper amount back in? Did you follow procedure to check the fluid level once all back together?

So that others don't have to google, these are the codes above:

P0306 — Cylinder 6 Misfire Detected

What it means:
The engine computer is seeing misfires on cylinder #6.

Common causes:

• Bad spark plug or ignition coil (very common on JKs)
  
• Faulty fuel injector on cylinder 6
  
• Vacuum leak near that cylinder
  
• Low compression (valve or piston issue — less common but more serious)
  

Severity:
⚠️ Moderate → Can cause rough running and damage the catalytic converter if ignored.

P0721 — Output Speed Sensor Range/Performance

What it means:
The transmission’s output speed sensor is giving readings that don’t make sense.

Common causes:

• Failing output speed sensor
  
• Wiring or connector issue at the transmission
  
• Dirty or damaged sensor tone ring
  
• Occasionally triggered by transmission control issues
  

Severity:
⚠️ Moderate → Can cause odd shifting, limp mode, or speedometer issues.

P1776 — Solenoid Switch Valve Latched in Low

What it means:
The transmission’s solenoid switch valve is stuck in the “low” position. This is a very well-known issue on Chrysler/Jeep automatics.

Common causes:

• Worn or sticking solenoid pack
  
• Contaminated transmission fluid
  
• Internal valve body wear
  

Severity:
🚨 High → Often causes limp mode (stuck in 2nd gear).

P1790 — Fault Immediately After Shift

What it means:
The transmission detected a problem right after a gear change.

Common causes:

• Secondary code caused by P1776
  
• Failing solenoid pack
  
• Valve body problems
  
• Transmission slipping or pressure issues
  

Severity:
🚨 High → Usually appears alongside other transmission faults.

 

Have a 2010 wrangler with new reman engine I bought. Has misfires on cylinders 1,2 and 6, have replaced injectors coil plugs wires and all sensors. Also installed new injector harness , engine harness and pcm. New doses misfires for about 3 days and now misfires are back, and ocm is hot to touch any help would be appreciated.