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P121B CEL on 2016 cat

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#1
Hello everyone.
I got the P121B code three days ago.

I got it while driving the car at normal speeds. I was actually merging onto a highway when it came on. I don’t think my driving style has anything to do with the CEL.

After doing some research I see that the code is for a malfunction in one of the Active Exhaust valves.

I went to the dealer this morning to see if what remains on my 5 year/ 60,000 mile power train warranty would cover this ......... it does not.

While I was there, I asked some basic questions about this particular code and they seemed to have a different opinion than what I’ve read during my research. They kept telling me that code was a “communication code”. They explained it as being an electrical issue.

After I mentioned to them that I thought it was an issue with the active exhaust valves they told me that was not the case. They even said that some people disconnect the active exhaust valves and don’t get a CEL.......... I know for a fact that claim is not correct. i left the dealership and I’m going to fix it myself.

2 questions for you guys.

1- is the P121B code actually an issue with the Active Exhaust Valves? Or am I wrong?

2- which of the two exhaust valves does this code refer to? Driver or passenger side?

if anyone has any leads on a website with good pricing on Mopar parts Let me know.

I know Steve white is a popular one, looking for more choices.
 

Paladin06

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#2
I removed the springs and wired the valves open on my 2019 Redeye with no lights or codes for almost a year now. Phillips Performance has an easy fix for those 2015 thru 2018 cars.
 
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Thread Starter #3
I removed the springs and wired the valves open on my 2019 Redeye with no lights or codes for almost a year now. Phillips Performance has an easy fix for those 2015 thru 2018 cars.
Can you elaborate on how you wired the valves open?
I might try to do this and remove the springs like you did as a fix.
 

Paladin06

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#4
Can you elaborate on how you wired the valves open?
I might try to do this and remove the springs line to u did as a fix.
Is your car a 2019?
 
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Thread Starter #5

Paladin06

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#6
Can you elaborate on how you wired the valves open?
I might try to do this and remove the springs line to u did as a fix.
Unhook the battery.

Jack the researchers of the car. Chalk the front wheels. (Safety first)

Remove the 4 bolts securing the black valve cover. Careful it is spring loaded.

Moved the valve to the full open position.

Use 0.020 steel safety wire to keep the valve open and secured it open by wrapping the wire around the exhaust pipe.

Reinstall the cover without the spring.

Hook up the battery and start the car.

Good luck.
 

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#7
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Thread Starter #8
thank you for the write up.

i guess they have changed some things regarding the exhaust valves on the 2019s.

I’ll see what Phillips performance offers.
 

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#9
thank you for the write up.

i guess they have changed some things regarding the exhaust valves on the 2019s.

I’ll see what Phillips performance offers.
I think it’s really software not hardware.
 
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Thread Starter #10
i agree with you. Most likely it’s software based changes.



can anyone confirm that P121B is a code for the passenger side active exhaust valve?

the info I found on line (in the old forum) seems to point in that direction. I want to be sure.
 

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#11
Here’s what I found. Check the for sale thread here. Some guys sell them if they just race their cats.

That code is for active exhaust valve #2 , usually a sensor needs to be replaced. There was a TSB for this back in 2015 that had the dealer re-flash the PCM (#18-035-15).
 
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Thread Starter #12
I’ll check the for sale threads, I didn’t think of doing that, great suggestion.

Im assuming that exhaust valve #2 refers to the passenger side. i should be able to figure out which side is malfunctioning once I get under the car and have my girlfriend cycle the ignition switch.

I read about that TSB as well. Seems to me like the TSB was issued to address a host of issues (One being the exhaust valve code).

I won’t buy anything until I get under the car and look and see whats going on down there. It may be something physically wrong with the flap inside the exhaust pipe. In which case, a new exhaust valve won’t be necessary.

hopefully I‘ll have time to get under the car tomorrow.

thank you for your help and suggestions paladin
 

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#13
I’ll check the for sale threads, I didn’t think of doing that, great suggestion.

Im assuming that exhaust valve #2 refers to the passenger side. i should be able to figure out which side is malfunctioning once I get under the car and have my girlfriend cycle the ignition switch.

I read about that TSB as well. Seems to me like the TSB was issued to address a host of issues (One being the exhaust valve code).

I won’t buy anything until I get under the car and look and see whats going on down there. It may be something physically wrong with the flap inside the exhaust pipe. In which case, a new exhaust valve won’t be necessary.

hopefully I‘ll have time to get under the car tomorrow.

thank you for your help and suggestions paladin
Check with dealer to see if your car was ever recall flashed?
 

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