P0135 / P0155 Codes

[waldo25]

Hi everyone, new here.
I’ve been dealing with these codes for a few months now and cannot figure it out. Below are the parts already replaced. Recently it’s started to shake a little when idling as if there’s a misfire. Press the gas and it won’t accelerate. If I press it harder I hear a loud pop and then it accelerates.

-Spark plugs (8)
-Ignition coil packs (8)
-O2 sensors (4)
-All fuses and relays work
-No air leaks
-Cold Air intake filter

 

[StockishS197]

What O2 sensor brand and are you sure you got the right upstream O2s? The downstream and upstream O2s are different.

Any other recent work or events that lead up to the codes? Having codes on both upstream O2s are suspect.

 

[86GT351]

What spark plugs did you use and what is the GAP on them?

 

[DieHarder]

Did you change anything before symptoms showed up? If so, what was it?

Are the coil packs OEM?

 

[waldo25]

I started throwing parts at it, soon as the issue happened. Issues started with original coil packs. I have after market performance ones now. I’ve always used Motorcraft spark plugs. O2 sensors I tried BOSCH & MOTORCRAFT.

 

[StockishS197]

I started throwing parts at it, soon as the issue happened. Issues started with original coil packs. I have after market performance ones now. I’ve always used Motorcraft spark plugs. O2 sensors I tried BOSCH & MOTORCRAFT.

For the avoidance of doubt, when you replaced the O2s, you are sure you bought UPSTREAM O2s and placed them in the first correct bungs ahead of the catalytic converters right (driver side upstream O2 is in the manifold, passenger side O2 is on the midpipe just after the ball and socket connector)?

Also don’t use Bosch O2s in these cars. They cause issues with slow heating.

 

[waldo25]

For the avoidance of doubt, when you replaced the O2s, you are sure you bought UPSTREAM O2s and placed them in the first correct bungs ahead of the catalytic converters right (driver side upstream O2 is in the manifold, passenger side O2 is on the midpipe just after the ball and socket connector)?

Also don’t use Bosch O2s in these cars. They cause issues with slow heating.

Yes, i actually took it to my mechanic that’s always worked on my car to replace them. The Motorcraft ones are currently on and issue persists. Parts were labeled and everything.

 

[waldo25]

Update - My mechanic believes it’s the computer module by the fuse box in the engine bay. I have started experiencing backfires now, to the point where I need to pull over and wait it out for a few minutes. Mechanic says he has checked for air leaks, all connectors, canister valve and everything is good.

 

[86GT351]

I started throwing parts at it, soon as the issue happened. Issues started with original coil packs. I have after market performance ones now. I’ve always used Motorcraft spark plugs. O2 sensors I tried BOSCH & MOTORCRAFT.

Are the spark plugs gapped properly? They are NOT gapped from the factory. I have seen it too many times here at the dealer when a car comes in after someone else replaced the spark plugs and just took them out of the box and installed without checking the gap!

 

[waldo25]

Are the spark plugs gapped properly? They are NOT gapped from the factory. I have seen it too many times here at the dealer when a car comes in after someone else replaced the spark plugs and just took them out of the box and installed without checking the gap!

I’ll ask him to check that. Not too knowledgeable like that. But I change my spark plugs and never gapped myself, my tune up is coming up so maybe it’ll fix something. I figured Motorcraft would be trustworthy lol all these years I’ve gotten their spark plugs and never gapped

 

[86GT351]

I’ll ask him to check that. Not too knowledgeable like that. But I change my spark plugs and never gapped myself, my tune up is coming up so maybe it’ll fix something. I figured Motorcraft would be trustworthy lol all these years I’ve gotten their spark plugs and never gapped

Motorcraft is fine. My point is too many people/mechanics take them out of the box and install without checking Gap these days.

 

[07 Boss]

I don't know if this will help. Back in the day Ford used to list two different part numbers for the front and rear sensors. But now if you go to ford they list one part number for all four sensors. I was having some issues with my sensors until I went and looked up the original NGK part numbers for the front. Since getting the original NGK sensors in there I haven't had any issues.

But what strikes me as weird is that it is a heater circuit malfunction as opposed to a stuck rich or lean code. That is usually something that pops up when you relocate the sensors with like headers.

 

[waldo25]

I don't know if this will help. Back in the day Ford used to list two different part numbers for the front and rear sensors. But now if you go to ford they list one part number for all four sensors. I was having some issues with my sensors until I went and looked up the original NGK part numbers for the front. Since getting the original NGK sensors in there I haven't had any issues.

But what strikes me as weird is that it is a heater circuit malfunction as opposed to a stuck rich or lean code. That is usually something that pops up when you relocate the sensors with like headers.

Yes, my mechanic is stumped and can’t figure it out. The only thing he can’t point at is the ECU under the engine, next to the fuse box. I changed out the evap canister because that’s the other code and still won’t clear. Mechanic is saying the computer is not registering the O2 seonsors or the canister. He’s volt tested all the sensors and canister, there’s voltage.

 

[waldo25]

Tune up was done today. All spark plugs (gapped to specs), Evap Canister, Oil change, new air filter, new belt and checked for any loose fittings. Cleared the codes. After a 5 mile drive, they came back on. Only thing left is the ECU as the mechanic suggested. Anything I need to lookout for when replacing ECU? Whether it’s used from another Mustang or new?

 

[Eman]

Your codes are for the O2 HEATER circuit, do the O2 sensors have voltage for the heater circuit and ground? Shouldn't cause a performance problem once heated up. What's the fuel pressure? Ford ECU's are usually pretty good.

 

[Juice]

Mode 6 data should display O2 heater current draw. I can look at that with my phone.

I would try unplugging one of the upstream sensors to see what additional codes pop up.

 

[waldo25]

Sorry for the late update. Have not had time to mess with the Mustang until today. I don’t have the “Mode 6” on my scanner. Attached are some pictures of the values I got while idling and driving. New code is for misfire on cylinder 3. Checked spark plug and coil plug. Switched it out for another cylinder and still on. Came on after a cold start at highway speeds.

 

[Eman]

Does it have a misfire you can feel? Misfire can be an injector also. Did you physically check voltage and ground with a multimeter at the O2 sensor?

 

[waldo25]

When that cylinder misfire came on yes, but not since. Revs to go down sometimes at idling after driving for a bit and right before the backfire and loss of power starts. Once I pull off to the side and let it sit for a while it all goes away