Automatic Transmission Control Module problems of the 2015 Infiniti Q50

While operating the vehicle, the transmission suffered an abrupt failure resulting in diagnostic trouble code (dtc) p0720 (output speed sensor circuit). Further diagnostic inspection revealed a complete internal failure of the integrated valve body assembly, which houses the transmission control module (tcm), solenoids, and output speed sensors. The failure caused an immediate loss of gear selection, restricting the transmission to 3rd gear ("limp mode"). Attempting to accelerate beyond 3rd gear causes violent vehicle shaking, severe hesitation, and an inability to maintain traffic speeds due to the tcm losing signal input from the speed sensors and solenoid circuits. This total valve body/tcm failure creates a critical safety hazard. Sudden restriction to 3rd gear without warning on highways or during turn movements leaves the vehicle unable to match surrounding traffic speeds, creating an immediate risk of a rear-end or side-impact collision. The vehicle has been strictly maintained according to manufacturer schedules. Because Nissan/Infiniti designed the tcm and speed sensors as an integrated unit inside the hydraulic valve body, a sensor failure requires replacing the entire valve body/tcm unit—a repair quoted at over $3,000, with complete transmission replacement exceeding that cost. This valve body/tcm failure mode is widely documented among Infiniti Q50 owners sharing the re7r01a 7-speed automatic transmission platform, indicating a widespread electronic and mechanical defect that threatens driver safety.

While driving my 2015 Infiniti Q50s, the transmission suddenly suffered a catastrophic electronic failure, causing the vehicle to immediately drop into "limp mode. " this resulted in a sudden and dangerous loss of acceleration while operating in traffic. A diagnostic scan revealed trouble codes p0500 and p0720 (output speed sensor circuit). However, following Infiniti's official technical service bulletin (TSB itb19-040), the actual failure was the transmission control module (tcm), which is permanently integrated into the transmission control valve body inside the transmission. Because the speed sensor cannot be replaced independently of the integrated module, I was forced to pay out-of-pocket to replace the entire transmission control valve body assembly and have a dealership program the new unit. This is a widely documented, premature failure on this vehicle platform that creates an immediate highway safety hazard when the vehicle drops power without warning.

Transmission valve body failed while driving which caused shifts to be limited. It could have caused an inability to shift at all, which is a safety issue. This issue has been inspected and confirmed by an independent shop. No warning signs were present before the failure. Furthermore, this issue is well known to Infiniti. It’s caused by breakdown of the transmission fluid overtime, causing a reduction in the cooling capacity of the fluid. But Infiniti says that the fluid should be lifetime. This overheating causes the tcm on the valve body to fail. If it failed while I was going at a highway speed I could have been injured.

Just over 1 week ago, I was leaving a parking lot and driving back to my home when my car wouldn't accelerate past about ~10-15 miles per hour and wasn't shifting gears. When I took my foot off the gas pedal, the gear just dropped immediately from above third to first gear and the car shook. I first noticed this when already out of the parking lot and pulling off from a median onto the road, with no engine light or other warnings. I quickly pulled into the turn lane where there wasn't traffic and turned the car off and back on. It was the same but luckily I was in eyes view of my apartment, so I drove under 10 mph and made it home. I took the vehicle to a transmission service center and the error code that came up on the computer was (p0500 - vehicle speed sensor a), which the service center said is an issue with the "valve body" inside the transmission, specifically the "tcm - transmission control module" that sits on top of the valve body. I contacted multiple Infiniti service centers and they all confirmed that the valve body for my vehicle (part# 31705-x133a) is back ordered by over a month and could be longer until they have it. They do not sell the transmission control module separately. The valve body was quoted to me for $2200 for the part alone. I attempted to install an aftermarket valve body and a new error code came up on the computer (po720 - output speed sensor circuit). I kept the original valve body and will hold onto it. Doing some more research, this appears to be a common issue with the Infiniti Q50 - [xxx] in addition to the reddit thread above, a quick google search for Infiniti error codes p0500 and po720 point to multiple sources indicating the same common experience and outcome. My vehicle has 110k miles and users in the reddit comments are also reporting the same issue with the tcm transmission control module occurring between 85k - 100k miles in all cases. Information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552(b)(6).

The valve body/tcm shorts out on the car unexpectedly and can happen at any time causing the car to be unable to go past third gear. This is an known problem with 2014-17 Infiniti Q50 & there is a service bulletin issued by Infiniti associated with this problem published in November 2019. This vehicle was inspected by Infiniti dealership and they confirmed the issue. There was no warning light or prior to this event. After the failure this codes popped up p0720. Repair was ~$3500.

The valve body/tcm. Yes the vehicle is available for inspection. The valve body/tcm shorts out on the car unexpectedly and can happen at any time causing the car to be unable to go pass third gear. This can occur on the freeway, or when trying to avoid an accident. This is an known problem with Infiniti’s & there is also an service bulletin associated with this problem. This vehicle has be inspected by the dealership and they confirmed the issue. There are no warning light or and thing prior to this event. After the failure this codes popped up p0720 & p0500. This occurred on Aug 13, 2022.