DTC codes p0420/p0320 on a new Mustang GT

[Andyjamo1961]

Hi

I've got a new UK RHD March 16 reg Mustang GT manual reg AJ16GTO

I have a couple of DTC codes that keep popping up the car has done 5200 miles and recently the engine management light has come on three or four times. On investigation the code 0420 shows catalyst efficiency below Threshold bank 1 (only once it came up 0320 Bank 2)

I have a JLT Cold Air induction with the engine tuned to accept the mass air / 93 octane and an MRT Resonator delete H pipe from new and all runs beautifully, the codes started appearing about 500 miles ago.

Even after I put the stock air box back on with the stock tune and the engine light still came on showing code 0420, thinking it might be an exhaust leak I even had the exhaust bolts all re tightened and the light came on again on a gentle cruise but after a reset I drove for another 100 miles without problem.

Before I take it to the dealership What do you guys think

Cheers Andy

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[jasonstang]

That's weird. Could be a bad downstream o2 sensor.

 

[Andyjamo1961]

Does anyone think that the JLT tune might damage the cat long term?

 

[Andyjamo1961]

Could an O2 sensor fail that new, & wouldn't it just keep showing the code right after being reset if it had failed or possibly it could be an intermittent fault

 

[jasonstang]

Could an O2 sensor fail that new, & wouldn't it just keep showing the code right after being reset if it had failed or possibly it could be an intermittent fault

The only way to find out is hook a sensor to the exhaust pipe to actually look at the exhaust gas.
It's either failed or coated in carbon due to the tune.
Although I have had cat failed in 5000 miles on an RX-8 due to excessive idling from the previous owner.

 

[Andyjamo1961]

The only way to find out is hook a sensor to the exhaust pipe to actually look at the exhaust gas.
It's either failed or coated in carbon due to the tune.
Although I have had cat failed in 5000 miles on an RX-8 due to excessive idling from the previous owner.

I'll put the CAI back to stock then wait for the next DTC code before getting the dealer to check it, will they be be able to detect that the JLT has been on and the tune has been changed. Not wanting any argumement over the warranty

 

[Chameleon]

Sounds like a tune issue. Good luck.

 

[redline727]

I'll put the CAI back to stock then wait for the next DTC code before getting the dealer to check it, will they be be able to detect that the JLT has been on and the tune has been changed. Not wanting any argumement over the warranty

I believe they are able to see when the last flash was performed, they wont know why or for what or how many times, just the last time it was done. At that point it will be obvious they didnt flash it under warranty for any reason based on service history. So I am sure they may ask you. I could be wrong but this is what I have been told.

 

[Wvmike]

If they look for it, they will be able to tell it has been flashed. They may or may not look for it. It depends on your dealer. If you put it back to stock, they may not look for it since you haven't had a major failure.

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