2009 Mazda5 (5 Speed Auto) P0720 Fixed

crownjewel

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Mazda 5
I just thought I'd share this because I found conflicting information out there and a few dropped threads. My vehicle: 2009 Mazda 5 Sport (5 Speed Auto) with 122K miles. A few weeks ago while accelerating on the street I experienced hesitation in the transmission, then the AT light turned on for a second then turned off, then a CEL. The transmission shifted normally after that, the speedometer worked fine, and everything continued to work as usual. The CEL read as P0720 Output Shaft Sensor Circuit. I used the code reader to clear the code, but within a few days I experienced the same thing and CEL turned on again with the same code. Despite the dealer diagrams it was confusing to tell exactly where the the sensor nearest the output shaft was.

From my research, I found that the Mazda 3 and Mazda 5 with 5 Speed Auto Transmissions have a total of 3 speed sensors:
One FN0121550 (located underneath the intake airbox), and two FN1221551A (one is located under the battery, the other is located under the car, towards the back of the transmission. To make matters more confusing, Mazda does not label their sensors with their corresponding use, example: Generator Pulse Sensor and Turbine Speed Sensor.

I first replaced FN0121550 under the intake air box, but the car threw CEL P0720 once again. I then replaced FN1221551A located under the battery, but the car registered the same P0720 again within 2 days. The final fix was replacing the second FN1221551A located under the car, rear of the transmission and NEAR THE OUTPUT SHAFT. The output shaft is clear as day once you're underneath the car.

Anyway, I hope this helps someone. All sensors were OEM purchased from Mazda, each was between $90-$100 retail. Aftermarket versions can be found for about half.

Edited 9/5/17
After one week of replacing all three speed sensors with brand new OEM units as explained above, the car once again threw P0720 CEL. The last ditch effort before taking the car to a dealer was to replace the Transmission Control Module (TCM) myself. The TCM is much more expensive (near $500.00) than the speed sensors, but easy to do so I gave it a shot. It's located underneath the battery. Once the battery and battery tray are removed, you'll need to remove a black bracket that has a weight on one end. It's held on with two bolts (17mm, I believe). The TCM itself is held on with three 10mm bolts, and they are not the easiest to get to. You'll also need to some pliers to squeeze and remove a wire loom fixture attached to the top of one of those 10mm fasteners. My old TCM was part# L39C189E1C. My new unit was brand new OEM purchased from the dealer (verified correct replacement part# with my VIN#), new part number is L39C189E1E. It's been over 1 week since this has been installed and no more problems. I'll edit once again if any other problems occur.

Edited 10/3/22
TCM had not been relocated and is still in the original location, just maintaining regular transmission fluid changes since the original date of my post, and the transmission is still working great.
 
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How many miles do you have on your 5. I also have a 09 GT and currently trying g to fix an issue with probably MAF sensor. I have abt. 92k miles. Is it common on the 5 for all these sensors to need replacement around this time?
 
How many miles do you have on your 5. I also have a 09 GT and currently trying g to fix an issue with probably MAF sensor. I have abt. 92k miles. Is it common on the 5 for all these sensors to need replacement around this time?


I have around 122k miles at the moment. Apparently all three of my original speed sensors were working fine since I replaced all three of them and each, one by one, and the CEL returned after each one was replaced. Since the recurring P0720 CEL stopped once I replaced the TCM, I'm positive this (TCM) is what was malfunctioning in the first place. I tried to save money by replacing things in order of least expensive to the most expensive, but that didn't work in this case.
 
Thanks for the detailed info @crownjewel . I'm experiencing the exact same scenario (P0720 codes, etc.). I've replaced 2 of the 3 speed sensors and am still experiencing the issue. The only one I haven't changed is the FN1221551A under the battery. I'm going to go ahead and get my TCM "repaired"/"remanufactured" as I don't want to pay for a brand new unit. Will re-post to let everyone know what happens.
 
Thanks for the detailed info @crownjewel . I'm experiencing the exact same scenario (P0720 codes, etc.). I've replaced 2 of the 3 speed sensors and am still experiencing the issue. The only one I haven't changed is the FN1221551A under the battery. I'm going to go ahead and get my TCM "repaired"/"remanufactured" as I don't want to pay for a brand new unit. Will re-post to let everyone know what happens.
You're welcome. It's been almost 5 years and 45k additional miles since my post and that brand new OEM TCM resolved all of my transmission issues. I hope it works out for you.
 
Eastern100 - Thought I would jump in here. I decided to buy a new TCM module (around $500) about 2 months ago. It came pre-programmed (plug and play). I zip-tied it to my brake lines to get it up in some fresh air. After installing it all my shift issues disappeared. I have a 2007 Mazda 3 hatchback with 96K miles. I had replaced all 3 of the speed sensors but the fried TCM was definitely what was causing the shifting problem. Good luck.
 
Thank you for your reply. It seems like everyone is trying to replace their sensors and their fluid, etc, I’ve heard 2 TCM stories in a row with great results. Im just wondering if a used one would give the same positive result instead of a $500 new one.
 
I hear what your saying - I came really close to going down the path of getting a remanufactured TCM because of the cost of a new one. When I began looking for a used TCM I couldn't find anything except remanufactured (you send yours in and they send you a remanufactured unit back). I think it comes down to how much of risk are you willing to take. More than likely a remanufactured TCM would work fine. I just decided to take the hit and reduce the risk somewhat.
 
I got my TCM fixed for the 2008 mazda5, this really works as it fixed hard shifting / solenoid errors issue for good. I would absolutely recommend going this way.
 
Hey, did you have to get the TCM programmed at the dealer or was it just plug and play?

Thanks.
Hello. The TCM was purchased brand new from the Mazda dealership. It was an all new unit and no programming was done at the dealership as far as I'm aware. No transmission issues have occurred ever since I replaced it.
 
I would highly recommend a refurbished TCM. Mazda uses very lousy soldering from the factory and places it on the transmission. One of the hottest parts of the car. Believe it or not the refurbished are fully taken apart and soldered much better and solid. Also it would be a good idea to relocate the replacement along the firewall with zip ties to keep the massive heat away from it.
 
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