MUSTANG o2 Sensor PLEASE HELP

[Carter9]

Hey guys. I have a 2009 Ford mustang GT. Every year since ownership I’ve gotten an o2 sensor code whether lean or rich or circuit and I replace it every year and every year it’s gone off. but not this year. Since august 23 I haven’t been able to get it inspected. As of now, it’s the p0153, slow response in o2 sensor circuit. I’ve replaced all sensors with the basic ones (cheap ones from autozone). I’ve replaced the catalytic converter. Tried everything. Some people say to get the ford o2 sensors instead of the cheap ones. Some people think it’s a fuel rail sensor. Some people think it’s a wiring issue or fuses. I really need to help to get it fixed and inspected. Im wondering if anyone else has had thing problem. It’s an 09 GT if that helps. Any response would help. Thank you.

 

[AHaze]

Is it always a P0153? That would be the driver's side so you can eliminate anything that isn't specific to that side like the fuel rail pressure sensor.
You can swap the upstream sensors side to side and see if the code follows to the other bank. If so, there's your answer. If not, wiring/connectors is where I would look next.

 

[Carter9]

it hasn’t always been but that’s the code that that is the only one on right now. I’ll either switch sides like you said or get a new o2 sensor for the drivers side. I’m gonna have ford run a diagnostic this weekend, I feel like it’s the easiest option so I can get to the bottom of it. Thanks

 

[MrBhp]

Ford might be as useful as the previous "help" you've had so far. You really should swap the sensors side to side before spending another dime.

 

[Juice]

You replaced sensor, code stayed, probably not the sensor.
Pull the sparkplugs on the problem side, post pic of plugs. While you have 4 plugs out, wouldnt hurt to pull other side plugs and do a compression test.

 

[07 Boss]

I used to get random O2 codes before I switched them back out to the NGK ones. Always seemed to have issues with bosch and even the ford replacements. I believe Ford uses the same part number for front and rear sensors but they used to be different. I don't know if that made a difference but the NGK ones have separate numbers for the front and rear.

 

[Carter9]

Okay so I switched the o2 sensors. So if it is the sensor, the code will reappear but in a different location??

 

[AHaze]

Okay so I switched the o2 sensors. So if it is the sensor, the code will reappear but in a different location??

If you swapped them left to right and the sensor is bad, you should get a P0133 which is the same slow response code but for bank 1, sensor 1 instead of bank 2, sensor 1.

 

[Squiggle05GT]

I've been dealing with an ongoing issue related to the Bank 1 Sensor 1 O2 sensor (upstream, passenger side) on my 2005 Mustang GT. I keep getting a P0135 code, which I believe is causing the engine to run rich. On cold starts, the car runs rough for about a minute, then smooths out, but the exhaust smells heavily of unburned fuel — almost like straight gas.

So far, I've replaced that specific sensor twice — once with a Bosch, and then with a TRQ sensor from American Muscle — but the code keeps coming back. I even replaced the PCM based on a shop's diagnosis, and that's where things really went south.

I ordered a PCM from ProTech Auto Systems and spent nearly $1,000, but after installing it, the car ran significantly worse — it felt like it was about to shut off. I ended up returning it and getting a refund, but the whole ordeal was a huge waste of time and money. Based on that experience, (I definitely don't recommend ProTech Auto Systems to anyone looking for a PCM replacement.)

To give some context, I initially took the car to a local shop for diagnostics, and they were the ones who misdiagnosed the issue as a faulty PCM. Looking back, they were way off. Now I'm considering taking it to MAK Performance to finally get a proper fix, because this is the only O2 sensor giving me problems — the others are fine. I had them all replaced when I took the car in to install BBK shorty headers.
At this point, I'm planning to try an NTK O₂ sensor, since I've read that Ford ECUs are very picky and often don't work well with Bosch, TRQ, or other aftermarket sensors. Hopefully, that'll finally resolve the issue once and for all.

 

[AHaze]

I've been dealing with an ongoing issue related to the Bank 1 Sensor 1 O2 sensor (upstream, passenger side) on my 2005 Mustang GT. I keep getting a P0135 code, which I believe is causing the engine to run rich. On cold starts, the car runs rough for about a minute, then smooths out, but the exhaust smells heavily of unburned fuel — almost like straight gas.

P0135 is a failure in the O2 sensor heater circuit and while I don't know exactly how that relates the PCM strategy, it makes sense to me that this would cause extra enrichment or at least prolong the amount of time the car spends in open loop on a cold start.
If you aren't getting other O2 sensor codes then the ECU is happy with the actual AFR signal once it gets up to operating temp and I'd say it's highly unlikely the brand of O2 sensor is your issue. Far more likely is that you have a wiring problem. Much like the OP, you can simply swap your upstream sensors side to side and see if the code follows if you want to be sure.

 

[bambam 06]

I've been dealing with an ongoing issue related to the Bank 1 Sensor 1 O2 sensor (upstream, passenger side) on my 2005 Mustang GT. I keep getting a P0135 code, which I believe is causing the engine to run rich. On cold starts, the car runs rough for about a minute, then smooths out, but the exhaust smells heavily of unburned fuel — almost like straight gas.

So far, I've replaced that specific sensor twice — once with a Bosch, and then with a TRQ sensor from American Muscle — but the code keeps coming back. I even replaced the PCM based on a shop's diagnosis, and that's where things really went south.

I ordered a PCM from ProTech Auto Systems and spent nearly $1,000, but after installing it, the car ran significantly worse — it felt like it was about to shut off. I ended up returning it and getting a refund, but the whole ordeal was a huge waste of time and money. Based on that experience, (I definitely don't recommend ProTech Auto Systems to anyone looking for a PCM replacement.)

To give some context, I initially took the car to a local shop for diagnostics, and they were the ones who misdiagnosed the issue as a faulty PCM. Looking back, they were way off. Now I'm considering taking it to MAK Performance to finally get a proper fix, because this is the only O2 sensor giving me problems — the others are fine. I had them all replaced when I took the car in to install BBK shorty headers.
At this point, I'm planning to try an NTK O₂ sensor, since I've read that Ford ECUs are very picky and often don't work well with Bosch, TRQ, or other aftermarket sensors. Hopefully, that'll finally resolve the issue once and for all.

To give some context, I initially took the car to a local shop for diagnostics, and they were the ones who misdiagnosed the issue as a faulty PCM. Please, tell us where they are so the rest of us do not go to the trouble you went through.

 

[Squiggle05GT]

To give some context, I initially took the car to a local shop for diagnostics, and they were the ones who misdiagnosed the issue as a faulty PCM. Please, tell us where they are so the rest of us do not go to the trouble you went through.

Oh yeah, these guys down here in Miami — Perez Autoworks — were the ones I originally went to. I gave them the benefit of the doubt when they told me the issue was with my PCM. I trusted them at the time, and I think they quoted me around $300 for the diagnosis. But looking back, there were definitely some red flags that they weren't completely sure what they were doing with my car.

They kept bouncing between screens on a customer-facing computer in the waiting room, looking at a wiring diagram that I honestly wasn't even sure was for my exact model. I don't know much about wiring myself, but their uncertainty didn't inspire confidence. They told me the harness wires going to the PCM tested fine, but I don't think they ever checked the O₂ sensor harness at all.

At one point, they tried installing a different PCM — they claimed it was from a 2005 Mustang and that "it should work!" They attempted to program it using one of my keys with their scan tool, but the car wouldn't start at all. After about an hour of trial and error, they realized the PCM was actually from an F-250 or F-350, not a Mustang. At that point, I was just mentally checked out.

In the end, they told me my original PCM was bad and offered to order a used replacement for around $600, but I decided I'd rather source one myself. That led to my experience with ProTech Auto Systems, which I explained in my other post. I really did trust them with my money at the time, especially after seeing forum posts where people had used them successfully. But you saw how that turned out — a major disappointment.

Now, I plan on going to MAK Performance and hoping they can finally give me the solution I've been chasing for over a year. This is literally the last issue holding me back from getting my Mustang where I want it to be. I've already done a complete timing rebuild on the car myself, which I'm still proud of — especially since I tackled it on my own.