P0733 on 2008-2013 Infiniti G37: Gear 3 Incorrect Ratio Causes and Fixes

What's Unique About the 2008-2013 Infiniti G37

The Infiniti G37 used a 5-speed automatic transmission in 2008 before switching to a 7-speed (Jatco RE7R01A, also called JR710E) from 2009-2013. This P0733 code is particularly notorious on the 7AT models. The issue is rarely a simple sensor or solenoid. More often than not, the problem lies within the integrated valve body and Transmission Control Module (TCM) assembly, a known weak point that can cause a variety of shifting problems. The TCM is submerged in hot transmission fluid, which is believed to contribute to its high failure rate. Owner forums like MyG37.com are filled with experiences of P0733, often accompanied by P0720, being resolved only by replacing this entire control unit.

Generation note: The 2008-2013 G37 is part of the V36 generation. However, the automatic transmission changed during this period. The 2008 model year used a 5-speed automatic, while 2009-2013 models used the 7-speed automatic (7AT). The 7AT is significantly more prone to the issues that cause a P0733 code, particularly valve body failure.

Symptoms You May Notice

• Check Engine Light is on
• Harsh, erratic, or delayed shifting, especially involving 3rd gear
• Transmission slipping (engine revs high but car doesn't accelerate properly)
• Vehicle enters 'limp mode,' often getting stuck in a single gear and unable to use manual/sport mode
• Noticeable loss of power and poor acceleration
• Inability to shift past a certain gear (e.g., 3rd gear)
• Whining or clunking noises from the transmission
• Decreased fuel economy

Most Likely Causes

1. Faulty Transmission Valve Body / TCM Assembly 🔴 High Probability The 7-speed automatic transmission (Jatco RE7R01A) used in 2009-2013 G37s has a well-documented history of valve body failures. The Transmission Control Module (TCM) is integrated into this assembly, and heat cycling from being submerged in hot fluid is thought to cause electronic failure. An Infiniti technician on a forum stated that when code P0720 is present, it's an 'off the bat valve body' replacement scenario.
   How to confirm: A professional technician will use a high-end scan tool to check for communication with the TCM and monitor solenoid performance and speed sensor data. If fluid level and condition are good, and especially if code P0720 (Output Speed Sensor Circuit) is also present, the valve body/TCM assembly is the primary suspect.
   Typical fix: Replace the entire transmission valve body assembly. 🎬 Watch this detailed walkthrough of the valve body removal and installation. It is typically sold as a pre-programmed, remanufactured unit that includes the TCM and all solenoids. Some owners purchase used units from low-mileage vehicles, but this carries risk.
   Est. part cost: $500 - $800 (Remanufactured/Used), $1500 - $2700 (OEM New)
2. Low or Dirty Transmission Fluid 🟡 Medium Probability These transmissions are sensitive to fluid level and condition. The 7AT does not have a traditional dipstick, making it difficult for owners to check. Overheating or high mileage can break down the fluid, reducing its hydraulic properties and potentially causing shifting errors or limp mode, especially under high load like going up a steep hill.
   How to confirm: A technician must lift the vehicle while it's level and running at a specific temperature to check the fluid level via the overflow plug on the transmission pan. 🎬 See how to properly check and fill your transmission fluid level. The fluid's color and smell will indicate its condition—it should be reddish and not smell burnt. A DIY procedure exists but is complex.
   Typical fix: Perform a transmission fluid drain-and-fill or a series of drain-and-fills. A full flush is sometimes debated on higher mileage vehicles. Use only the correct Infiniti Matic S ATF or a compatible equivalent.
   Est. part cost: $100 - $250
3. Internal Transmission Damage ⚪ Low Probability While less common than control system failure, prolonged driving with low fluid or a bad valve body can lead to overheating and wear on internal components like the 3rd gear clutch pack. In some rare cases, loose bolts on the valve body itself have been found to cause internal pressure leaks and incorrect gear ratio codes.
   How to confirm: This is a diagnosis of exclusion. If replacing the valve body and ensuring correct fluid level doesn't fix the issue, internal inspection is required. Metal shavings in the transmission pan are a strong indicator of mechanical failure.
   Typical fix: The transmission must be removed from the vehicle for a complete rebuild or replacement.
   Est. part cost: $2000 - $5000+

Rare But Worth Checking

• Faulty Transmission Speed Sensors: The input or output speed sensors can fail, but it's less common than a full valve body failure. On the 7AT, the output speed sensor is physically part of the valve body assembly, so a P0720 code (Output Speed Sensor Circuit) almost always necessitates replacing the entire unit, as the fault is often in the TCM's interpretation of the signal, not just the sensor itself.
• Wiring Harness or Connector Issues: Damage to the wiring leading to the transmission or a corroded main connector can interrupt signals, mimicking a component failure. This is worth checking before replacing expensive parts, though it is not a commonly reported solution for this specific code on the G37.

Diagnosis Steps

1. Scan for all diagnostic trouble codes. Note any other codes, especially P0720 or other gear ratio codes (P073x).
2. Check the transmission fluid level and condition. This must be done by a professional or experienced DIYer as there is no dipstick. The vehicle must be level and the fluid at a specific temperature (around 104°F/40°C) to check via the overflow plug. The fluid must be clean, at the correct level, and not smell burnt.
3. If fluid is low or dirty, perform a fluid and filter change with Infiniti Matic S ATF and re-evaluate. One drain-and-fill replaces about 4-5 quarts.
4. Inspect the transmission's main electrical connector for corrosion or damage.
5. If the problem persists, especially if P0720 is present, the next logical step for a G37 is to replace the valve body/TCM assembly. This is the most probable cause.
6. If a new, properly programmed valve body does not resolve the issue, suspect internal mechanical failure (e.g., clutch packs, loose internal bolts), which would require removing and disassembling the transmission.

Parts You'll Likely Need

• Transmission Valve Body Assembly (with TCM) (OEM #31705-X987A) — This is the most common failure point on the 7-speed automatic transmission in the G37 that leads to code P0733. It includes the integrated TCM and solenoids. The part number 31705-X987A supersedes several previous versions like 31705-X629D and 31705-X458C.
  Trusted brands: Hitachi (OEM), Rostra, Various Remanufacturers (e.g., Five Star Transmissions)
  OEM price range: $1500 - $2700
  Aftermarket price range: $500 - $800
• Automatic Transmission Fluid (Infiniti Matic S) — Required anytime the transmission pan is dropped for service, such as a valve body replacement. A full drain and fill requires approximately 9-10 quarts.

Related Codes That Often Appear With This One

• P0720 — Stands for 'Output Speed Sensor Circuit Malfunction.' On the G37's 7AT, the output speed sensor is integrated with the valve body. An Infiniti technician on a forum noted that P0720 is an 'off the bat valve body' replacement scenario, and its presence with gear ratio codes like P0733 strongly indicates a failed TCM.
• P0732 — Stands for 'Gear 2 Incorrect Ratio.' It is common to see multiple incorrect gear ratio codes together, which further points to a central control problem (the TCM/Valve Body) rather than a specific gear's mechanical failure.
• U0101 — Stands for 'Lost Communication with TCM.' This code can appear after a failed valve body replacement if the new unit is faulty, not programmed correctly, or if there's a connector issue, indicating the car's main computer can no longer talk to the transmission controller.

Technical Service Bulletins (TSBs) & Recalls

• ITB10-075: Addressed hard downshifts and other shifting complaints with a TCM reprogram.
• ITB12-027d: An amendment to a previous TSB for 2009-2012 models to address shift responsiveness issues like harsh downshifts and hesitation by reprogramming the ECM and TCM.

Platform-Specific Known Issues

• The 7-speed automatic (7AT) transmission in 2009-2013 models had several Technical Service Bulletins (TSBs) issued for harsh shifting and drivability complaints, like ITB12-027d, which involved reprogramming the TCM to address harsh downshifts and hesitation. This points to a history of control-related issues with this transmission, even before outright failure.
• The integrated design of the TCM within the valve body, submerged in hot transmission fluid, is believed to contribute to its high failure rate due to heat-related stress on the electronics.

Mechanic-Grade Diagnostic Values

• Input and Output Speed Sensor Resistance — expected: 215-275 ohms at 68°F (20°C). Failure: A resistance reading outside of this range indicates a faulty sensor.

Scan Tool Commands That Help

• Infiniti CONSULT: BATTERY SAVER Active Test — While not directly for P0733, this BCM test can help verify communication and power supply integrity to various control modules, which can be a preliminary step before focusing on the TCM.
• Infiniti CONSULT or compatible high-end scanner: Transmission Adaptation/Re-learn Procedure — This is required after replacing the valve body/TCM assembly to make the new unit learn the vehicle's specific shift characteristics. Failure to perform this can result in poor shifting even with a new part.

Wiring & Ground Locations

• TCM Connector — The main harness connector for the TCM is located on the outside of the transmission housing, typically on the passenger side. The TCM itself is inside the transmission, mounted to the valve body.. This external connector is a key point for checking for corrosion or damage before assuming the internal TCM has failed. All signals for speed sensors and solenoids pass through here.
• Main Engine/Transmission Ground Points — Key factory ground points are located on the passenger side strut tower, near the intake filter, and at the center rear of the engine on the lower plenum.. Poor grounding can cause erratic behavior in electronic modules, including the TCM. While not a common cause for P0733 specifically, ensuring these grounds are clean and tight is a fundamental step in diagnosing any electronic issue on the VQ engine platform.
• BCM (Body Control Module) Connector M119 — Located behind the left end of the dashboard.. The BCM communicates with the TCM over the CAN bus. A wiring diagram shows that CAN-L and CAN-H lines connect here, making it a potential diagnostic point for communication issues (like a U0101 code) that can sometimes accompany transmission faults.

Real Owner Repair Stories

• Reddit user VqCaden on r/G37 (2011 Infiniti G37, 117k miles, 7-speed automatic) — Car would not shift properly or would go into a false neutral state. Threw codes P0733 and P0720.
  ❌ Tried (didn't work) Two transmission drain-and-fills., Replacing the transmission filter., Resetting the TCM.
  ✅ What actually fixed it The issue was resolved by replacing the entire transmission valve body assembly. An Infiniti technician in the thread confirmed that getting P0720 alongside a gear ratio code is an 'off the bat valve body' replacement scenario for the dealership.
• Reddit user _81Levi21_ on r/G37 (2013 Infiniti G37x) — Transmission wouldn't shift, RPMs were erratic, revving to 5-6k before a harsh shift, couldn't get past 3rd gear, and manual mode would not engage. Codes P0500 and P0720 were present.
  ❌ Tried (didn't work) A transmission shop diagnosed it as needing a full transmission replacement for over $5,000.
  ✅ What actually fixed it The owner diagnosed the issue as a failed valve body/TCM based on extensive research. They ordered a pre-programmed, rebuilt valve body from Nexenzo for $649 and planned to install it themselves, which resolved the symptoms.

OEM Part Supersession History

• 31705-X629D → 31705-X987A — Part revision and update by the manufacturer.
  Heads up: While valve bodies may be physically the same across different G37 models (RWD vs AWD), the TCM programming is specific. A used valve body from a different model will require reprogramming by a dealer or specialist to function correctly in the recipient car. Some remanufacturers offer pre-programming to the vehicle's VIN.
• Multiple older versions → 31705-X986E — Part revision for 2010-2015 models.
  Heads up: Sellers like Nexenzo list part number 31705-X986E for 2010-2013 G37 models and require the VIN to pre-program the unit, highlighting that compatibility is tied to software, not just physical fit.

Model Year Variations Within This Range

• 2009-2012 (approx.): Earlier VQ37VHR engines used a paper-based rear timing cover oil gallery gasket that is prone to failure, leading to catastrophic loss of oil pressure. While not directly related to P0733, it's a major failure point on earlier G37s. Models from 2012/2013 onwards received an updated metal gasket. A car with low oil pressure can exhibit various drivetrain issues, although it's not a direct cause of P0733.
• 2009 vs 2010+: The 2009 model was the first year for the 7AT. Later models received infotainment and minor cosmetic updates. There were also running software updates for the transmission; Infiniti released a technical service bulletin (ITB10-075) for a transmission reprogram available for 2009-2011 models to improve shift quality, indicating software evolution during this period.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Oil Gallery Gasket Failure 🔴 High — Common on pre-2012 models, typically surfaces between 80k-150k miles. The original paper gaskets fail, causing internal oil leaks and catastrophic loss of oil pressure.
• Concentric Slave Cylinder (CSC) Failure (Manual Transmission Only) 🔴 High — Extremely common on 6MT models at any mileage. The plastic OEM CSC fails, causing the clutch pedal to stick to the floor and rendering the car undriveable. Often replaced with a heavy-duty aftermarket 'CSC delete' kit.
• Melting / Sticky Dashboard 🟡 Low — Very common on cars frequently exposed to heat and sun, typically appearing after 5-8 years. The dashboard material degrades, becoming sticky or gooey to the touch.
• Clock Spring Failure 🟠 Medium — A common failure leading to the horn, steering wheel controls, and airbag light becoming inoperative. Usually occurs at higher mileage.
• Rear Timing Cover Oil Leak 🟠 Medium — A leak can develop from a plate on the rear of the engine's timing cover, often requiring significant labor to access and reseal.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used valve body from a low-mileage donor car can be a cost-effective option if you are on a tight budget, but it is a significant gamble. The failure is due to heat and electronics degradation, so even a used part has a limited lifespan. It makes most sense for a DIY repair where the labor cost is zero, and the risk is only the cost of the part and fluid.

Donor-vehicle mileage cap: roughly under 60000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Verify the exact part number matches or is compatible with your VIN.
• Obtain the VIN from the donor car to check its service history if possible.
• Inspect the electrical connector pins for any signs of corrosion or damage.
• Ask for a warranty or return period from the seller (junkyard or online parts reseller).

Aftermarket brands forum-validated for this vehicle:

• Nexenzo (Remanufactured, Pre-programmed)
• Sonnax (Offers repair kits and components for valve bodies, but not full assemblies)
• IPT (Import Performance Transmissions - Offers upgraded/performance valve bodies)

Brands owners have reported issues with on this vehicle:

• Unbranded, non-programmed units from marketplaces like eBay or Amazon can be risky, as they often require dealer programming that may fail or be refused, negating any initial cost savings.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0720 — Output Speed Sensor Circuit. This is the most critical companion code. The sensor is integrated into the valve body/TCM assembly on the G37. When P0720 appears with P0733, it is a very strong indicator that the entire valve body/TCM unit has failed.
• P0729 — Gear 6 Incorrect Ratio. This is a companion code to P0733 (Gear 3 Incorrect Ratio). It indicates the same type of fault but in a different gear, pointing towards a systemic problem like low fluid, a failing valve body, or internal pressure leaks affecting multiple gear circuits.
• P0735 — Gear 5 Incorrect Ratio. Similar to P0729, this code signals an incorrect gear ratio in 5th gear. Seeing multiple P073x codes together makes a single component failure (like a specific clutch pack) less likely and a control system failure (valve body/TCM) more likely.
• P0500 — Vehicle Speed Sensor 'A' Circuit. This code can appear with transmission faults because the TCM relies on accurate speed sensor data to command shifts. A fault here can confuse the TCM, potentially leading it to set incorrect gear ratio codes like P0733.

Frequently Asked Questions