P0733 on 2019-2023 Ram 2500 6.4L Hemi: Gear 3 Incorrect Ratio Causes and Fixes

What's Unique About the 2019-2023 Ram 2500

For this specific Ram 2500 with the 8HP75 transmission, code P0733 is a well-documented issue. Ram has issued a Technical Service Bulletin (TSB 21-016-20) acknowledging that a software glitch can cause this code and other shifting issues on 2019 models. Owner forums frequently describe a standard dealer diagnostic path: first, apply the software update; if that fails, suspect the valve body; and if metal is found in the pan, proceed with a full transmission replacement, which is often covered under the vehicle's 5-year/60,000-mile powertrain warranty.

Symptoms You May Notice

• Check Engine Light is on
• "Service Transmission" message on the dashboard
• Harsh, jerky, or delayed shifts, particularly into 3rd gear
• Transmission slipping (engine RPMs increase without a corresponding increase in vehicle speed)
• Vehicle enters "limp mode" (gets stuck in a single gear, often 3rd or 4th)
• A noticeable bump or clunk during shifts
• Hesitation or refusal to shift at low speeds

Most Likely Causes

1. Transmission Control Module (TCM) Software Issue 🔴 High Probability → Shop Transmission Assembly Ram issued TSB #21-016-20 specifically to address P0733 and harsh shifting on 2019 models with the 8HP75 transmission via a software update. Another TSB, 21-007-20, addresses prematurely setting P0733 in 4-Lo on some 2020 models.
   How to confirm: A Ram dealer or a qualified shop with a wiTECH scan tool can check the current software calibration ID against the latest version and see if the update from TSB 21-016-20 applies to the vehicle's VIN.
   Typical fix: Reprogramming (flashing) the Transmission Control Module with the latest software version. The TSB notes that transmission adapts should be cleared after the flash if P0733 was the concern.
   Est. part cost: $0-$250
2. Faulty Transmission Valve Body 🟡 Medium Probability → Shop Transmission Valve Body The valve body, which contains solenoids to direct hydraulic fluid, can fail and cause pressure losses or incorrect gear engagement. It's the next logical mechanical part to inspect after a software update fails to resolve the issue, and a common failure point on ZF 8-speed transmissions.
   How to confirm: A technician can perform pressure tests and command solenoid function tests using a diagnostic scan tool. Visual inspection for debris in the valve body passages is necessary upon removal.
   Typical fix: Replacement of the entire valve body assembly. This is done by removing the transmission oil pan. 🎬 See this ZF8HP75 valve body overhaul walkthrough
   Est. part cost: $800-$1500
3. Internal Transmission Failure ⚪ Low Probability → Shop Transmission Assembly While less common on a newer truck, a failure of an internal component like the 'D' clutch pack can cause this code. This is a known, though less frequent, failure mode 🎬 Watch: Complete ZF8HP75 transmission teardown and inspection in the wider ZF 8-speed family.
   How to confirm: The definitive sign is finding a significant amount of metallic debris or clutch material in the transmission oil pan during a fluid or valve body service. Dealers are often required by Ram to drop the pan and inspect for metal before authorizing other major repairs.
   Typical fix: Complete transmission replacement or rebuild. For vehicles within the powertrain warranty period, this is often replaced as a full assembly by the dealer.
   Est. part cost: $4000-$8000

Rare But Worth Checking

• Low or Dirty Transmission Fluid: → Shop Transmission Assembly While a common cause for transmission codes generally, it's less likely to be the root problem on this specific platform compared to the TSB or valve body issues, especially on lower-mileage trucks. The 8HP75 is a 'filled for life' unit with no dipstick, so checking the level is a complex procedure that must be done by a professional at a specific temperature (86°F-122°F).

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner. Note any other transmission-related codes.
2. Contact a Ram dealer with the vehicle's VIN to check if TSB 21-016-20 (for 2019 models) or TSB 21-007-20 (for 2020 models) is applicable and has been performed.
3. If the software is outdated, have the TCM flashed. This is the most likely and least expensive fix and should be the first step.
4. If the code returns, the vehicle must be taken to a qualified transmission shop or dealer for hydraulic and mechanical diagnosis.
5. A technician will lift the vehicle on a level hoist and check the transmission fluid level and condition. This is a complex procedure for the 8HP75: the engine must be running, and the fluid temperature must be between 30°C (86°F) and 50°C (122°F). Fluid is added via the fill plug until it trickles out.
6. If the fluid is full and clean, the next step is to inspect the valve body. The technician will drop the transmission pan.
7. While the pan is off, it will be carefully inspected for metal shavings or clutch debris. This is a critical step.
8. If significant debris is found, it confirms internal mechanical failure, and a transmission replacement will be recommended.
9. If no debris is found, replacing the valve body is the next logical repair.

Parts You'll Likely Need

• Mopar 8 & 9 Speed ATF (OEM #68218925AB) — This is the required fluid for any service involving opening the transmission, such as a valve body replacement or filter change.
  Trusted brands: Mopar
  OEM price range: $25-$40 per quart
  Aftermarket price range: $20-$30 per quart
• Transmission Valve Body (OEM #RL402284AA (replaces 68402284AA)) — If a software update does not fix the issue, a faulty valve body is the next most common cause. This part is for vehicles built before 04/09/21.
  Trusted brands: Mopar, ZF
  OEM price range: $1000-$1500
  Aftermarket price range: $500-$1000
• Transmission Oil Pan and Filter Assembly (OEM #68225344AA) — The filter is integrated into the pan and must be replaced during any major transmission service like a valve body or fluid change.
  Trusted brands: Mopar, ZF
  OEM price range: $200-$350
  Aftermarket price range: $150-$250

Technical Service Bulletins (TSBs) & Recalls

• 21-016-20: Released for 2019 Ram 2500/3500 trucks with the 6.4L Hemi, this TSB specifically identifies P0733-00 as a primary code fixed by a TCM software update. It also addresses other complaints like harsh garage shifts.
• 21-007-20: Applies to some 2020 models and provides a software update to fix the premature setting of P0733, P0731, and P0734, particularly when operating in 4-Lo range.
• S2621000003 REV. A: A general diagnostic guide for various 8-speed transmissions, including the 8HP75. It advises that fluid smell alone is not an indicator of failure and that valve body replacement should be considered before transmission replacement.

Platform-Specific Known Issues

• A software glitch addressed by TSB #21-016-20 is a very common cause for this code on 2019 models with the 8HP75 transmission.
• Forum reports confirm a common dealer diagnostic path: software update -> valve body diagnosis -> pan inspection for metal -> full transmission replacement under warranty.
• The 8HP75 transmission is 'filled for life' and has no dipstick, making a fluid level check a professional-only task that requires specific tools and temperature monitoring.

Mechanic-Grade Diagnostic Values

• Clutch Volume Index (CVI) for the 'D' Clutch — expected: Within a specific range defined by the manufacturer (e.g., 30-100). The exact range for the 8HP75 'D' clutch is not publicly specified but is available on dealer scan tools.. Failure: A CVI value that is too high indicates a worn clutch pack. A value below the range suggests a binding issue. A value of zero indicates a major hydraulic leak in that circuit, causing the TCM to stop measuring.
• Clutch Filling Time — expected: A value in milliseconds (ms) representing the deviation from a standard fill time. This is viewable on a wiTECH scan tool.. Failure: Large deviations from the zero set value can indicate hydraulic leaks or worn seals within a clutch circuit.
• Clutch Filling Pressure — expected: A value in millibars (mb) or PSI representing the deviation from a standard fill pressure. This is viewable on a wiTECH scan tool.. Failure: Significant deviations from the zero set value suggest problems with pressure regulation, potentially from the valve body or internal seals.
• Solenoid Coil Resistance — expected: General guidance for ZF solenoids is ~5 Ohms for PWM (Pulse Width Modulated) solenoids and ~10-15 Ohms for on/off solenoids. Specific OEM values for the 8HP75 are not published but should be consistent across the solenoids of the same type.. Failure: Infinite resistance (open circuit) or zero resistance (short circuit) indicates a failed solenoid coil.

Hidden / Shadow Codes Worth Checking

• P1DA8-00: Incorrect Gear Ratio Clutch A, B or D Defective. This manufacturer-specific code often appears alongside P0733 and points more directly to an internal clutch failure rather than a sensor or software issue. (see via Dealer-level scan tools like wiTECH or advanced aftermarket scanners (e.g., AlfaOBD, high-end Autel). Standard OBD-II readers will likely not show this code.)
• P1D92-00: Incorrect Gear Ratio - Clutch 4 Defective. Similar to P1DA8, this code provides further confirmation that the fault lies within one of the transmission's internal clutch assemblies. (see via Dealer-level scan tools like wiTECH or advanced aftermarket scanners.)

Scan Tool Commands That Help

• wiTECH or equivalent (Autel, AlfaOBD): Reset Adaptive Values — This function must be performed after replacing internal transmission components like clutches or the valve body. It erases the TCM's learned data about the old, worn parts, preparing it for a fresh learn cycle. This is typically done before the 'Quick Learn' procedure.
• wiTECH or equivalent (Autel, AlfaOBD): Quick Learn — This procedure is required anytime the transmission, valve body, or TCM is replaced, or after the adaptive values have been reset. It runs the transmission through a static test to establish baseline hydraulic and timing values for the clutches. The procedure gives on-screen prompts to shift the vehicle into different gears while stationary with the brake applied.
• wiTECH or equivalent: Transmission Adaptation Drive Learn Procedure — If shift quality issues persist after a 'Quick Learn', this more involved procedure may be necessary. It requires driving the vehicle under specific load and speed conditions (e.g., moderate acceleration to 40-50 MPH) while a technician monitors scan tool data to ensure the clutch adaptation counters are updating correctly.

Wiring & Ground Locations

• Engine Block Ground — A primary ground strap typically connects the engine block to the chassis/frame. While a specific diagram for the 2019+ Ram 2500 is not readily available, this is a critical connection to inspect for looseness or corrosion.. The TCM and its sensors rely on a clean ground path. A poor engine ground can introduce electrical noise, potentially causing the TCM to misinterpret sensor data and set false codes.
• TCM Connector Pins — At the main electrical connector for the Transmission Control Module (TCM), which is part of the mechatronic unit (valve body) inside the transmission pan on the 8HP75.. A poor connection at the main harness connector or a fault in the ground pins can cause logic errors within the TCM. For example, on other Ram transmissions like the 68RFE, specific pins (e.g., 37, 39, 51, 57) are designated grounds. Verifying the integrity of the equivalent ground pins on the 8HP75 connector is a valid advanced diagnostic step if electrical issues are suspected.

Real Owner Repair Stories

• 5thGenRams Forum user 'Phantom_h60' (2020 Ram 1500 (similar 8-speed logic)) — P0733 - Gear 3 Incorrect Ratio
  ❌ Tried (didn't work) A complete valve body replacement was performed at 9,000 miles for the same issue, but the problem returned.
  ✅ What actually fixed it Because the valve body replacement had already failed to resolve the issue, Ram authorized a complete transmission replacement under warranty, which permanently fixed the problem.

"I Checked Everything" — The Actual Cause

• For P0733, the equivalent of a 'smoke test clean' scenario is when a technician checks the transmission fluid and finds the level is correct and the fluid is clean and red, with no burnt smell. In this case, the owner or technician might assume the issue is minor or electrical. However, on this platform, clean fluid often masks the true cause, which is typically a software glitch (TSB), a failing valve body, or an internal clutch failure that has not yet produced enough debris to visibly contaminate the fluid.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Hemi Lifter/Camshaft Failure ('Hemi Tick') 🔴 High — Commonly reported between 60,000 and 120,000 miles, but can occur earlier. Often starts as a light ticking noise that progresses to a misfire code. (Ref: No specific recall, but it is a widely acknowledged issue. A class-action lawsuit has been filed regarding this problem.)
• Broken Exhaust Manifold Bolts 🟠 Medium — Very common issue, often noticeable by a ticking sound when the engine is cold that disappears as the engine warms up and the metal expands.
• Uconnect Infotainment System Glitches 🟡 Low — Owners frequently report issues like screen freezing, phantom touches, or connectivity problems with Apple CarPlay/Android Auto. Often resolved with software updates or a system reset. (Ref: Various software update TSBs are released periodically to address these concerns.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For a complex, electronically integrated transmission like the 8HP75, using 'used' parts is high-risk. A complete, low-mileage transmission from a reputable salvage yard (e.g., from a rear-ended vehicle) can be a cost-effective alternative to a new unit, but it carries no guarantee. A remanufactured transmission with a warranty is a much safer choice than a junkyard part.

Donor-vehicle mileage cap: roughly under 50000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Verify the donor vehicle's VIN to confirm mileage and model year compatibility.
• Ask for video proof of the donor vehicle running and driving, if possible.
• Inspect the fluid from the donor transmission. While not definitive, any signs of heavy metal flake or a severely burnt smell are red flags.
• Check the main electrical connector for any signs of damage, corrosion, or bent pins.

OEM-only on this vehicle (don't cheap out):

• Transmission Control Module (TCM) / Valve Body Assembly: The TCM is integrated with the valve body on the 8HP75. Due to the precise calibration and software matching required for the vehicle's VIN, a new OEM or professionally remanufactured and programmed unit is strongly recommended. A used valve body could introduce contaminated fluid and unknown wear into your system.

Aftermarket brands forum-validated for this vehicle:

• ZF: As the original equipment manufacturer, ZF-branded parts (like the pan/filter or valve body) are equivalent to Mopar OEM quality.
• Sonnax: Known for producing high-quality problem-solver parts for valve bodies and internal transmission components, often addressing OEM design weaknesses.

Brands owners have reported issues with on this vehicle:

• Unbranded or 'white box' solenoid kits and valve bodies from online marketplaces. These often have inconsistent quality control and can cause more issues than they solve due to incorrect calibration or material defects.

Real Owner Stories

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

Related OBD-II Codes

• P0731 — Related gear ratio code (Gear 1) that can be prematurely set on 2020 models in 4-Lo, addressed by TSB 21-007-20.
• P0734 — Related gear ratio code (Gear 4) often appearing alongside P0733 in 4-Lo conditions on 2020 models, fixed by the same software update.
• P0300 — A general misfire code that may eventually result from the 'Hemi Tick' (lifter/camshaft failure) known to affect the 6.4L Hemi engine.

Frequently Asked Questions