P0735 on 2020-2024 Ram 2500 6.7L Cummins: Gear 5 Incorrect Ratio Causes and Fixes

What's Unique About the 2020-2024 Ram 2500

The 68RFE transmission paired with the Cummins engine has known vulnerabilities that make it prone to this code. The overdrive (OD) clutch pack, which is responsible for 5th and 6th gear, is a widely documented failure point and often burns out, especially under heavy loads or with increased power from tuning. Additionally, the valve body can develop wear in critical bores, like the Solenoid Switch Valve (SSV) bore, leading to hydraulic pressure loss that starves the clutches of the clamping force needed to prevent slipping. While P0735 is a generic code, on a 68RFE-equipped Ram, it strongly suggests a significant internal issue beyond just low fluid, often preceding total transmission failure.

Symptoms You May Notice

• Check Engine Light is on
• Transmission will not shift into 5th gear
• Vehicle enters 'limp mode', often stuck in 4th gear
• Harsh or delayed shifting between gears
• Engine RPMs flare or spike without an increase in vehicle speed, especially during the 4-5 shift
• Transmission temperature warning light may illuminate due to slipping clutches generating excessive heat
• Noticeable loss of power, especially at highway speeds
• Torque converter shudder or issues with lock-up

Most Likely Causes

1. Low or Burnt Transmission Fluid 🟡 Medium Probability The 68RFE can run hot, especially when towing, which degrades fluid over time. A safety recall (ZA3 / NHTSA 22V-835) was issued for potential fluid expulsion from the dipstick tube due to heat and pressure buildup, which can lead to a low fluid condition.
   How to confirm: Check the transmission fluid dipstick for level and condition. The fluid should be bright red (Mopar ATF+4) and not smell burnt. If it is dark brown/black, has a burnt odor, or contains visible metal/clutch material, it is degraded and indicates internal damage.
   Typical fix: Perform a transmission fluid and filter change. Note: If the fluid is full of black, gritty clutch material, a fluid change is a temporary measure at best and will not fix the underlying mechanical problem.
   Est. part cost: $100-$200
2. Failing Transmission Solenoid Pack / Valve Body 🔴 High Probability The 68RFE valve body is known for issues with wear in the solenoid switch valve (SSV) bore, causing hydraulic cross-leaks and pressure loss to the clutch packs. A failing solenoid can also fail to direct pressure correctly to engage the 5th gear clutch. Sometimes, the bolts holding the solenoid pack to the valve body can loosen, causing cross-leaks.
   How to confirm: A professional technician can perform a line pressure test to check for low hydraulic pressure. A scan tool can also check for solenoid-specific fault codes. Visual inspection of the valve body for wear is required for a definitive diagnosis, which involves dropping the transmission pan.
   Typical fix: Replacement of the solenoid pack. In cases of significant wear, the entire valve body may need to be replaced or remanufactured with oversized components from brands like Sonnax.
   Est. part cost: $250-$1400
3. Burned Overdrive (OD) Clutch Pack 🔴 High Probability This is the most common major mechanical failure on the 68RFE leading to P0735. The stock clutches are thin and susceptible to burning out from heat and pressure, especially in tuned or heavily worked trucks. The OD clutch is used for 5th and 6th gear, and its failure is a classic 68RFE weak point.
   How to confirm: Dropping the transmission pan and finding a significant amount of black, gritty clutch material is a strong indicator. A definitive diagnosis requires transmission disassembly and inspection, where the clutch discs will appear blackened, warped, and worn down to the metal.
   Typical fix: The transmission must be removed from the vehicle and rebuilt. This involves replacing the overdrive clutch pack, steels, seals, and any other damaged components. This is often when owners choose to install upgraded, more durable aftermarket clutch kits.
   Est. part cost: $800-$2500+

Rare But Worth Checking

• Faulty Input or Output Speed Sensor: While less common for an isolated P0735, a failing speed sensor can send incorrect data to the TCM, causing a false gear ratio calculation. This would typically be accompanied by other codes like P0716 or P0721. A user on Turbo Diesel Register reported similar symptoms (stuck in 4th gear) that were resolved by replacing the output speed sensor.
• Failed Powertrain Control Module (PCM) or Transmission Control Module (TCM): In very rare cases, the control module itself can fail, leading to incorrect commands or calculations. This should only be considered after all mechanical, hydraulic, and wiring causes have been ruled out.
• Blown Accumulator Plate: Especially on trucks with transmission tuning that increases line pressure, the stock accumulator plate on the valve body can blow out. This causes a massive hydraulic leak that often destroys the overdrive and underdrive accumulators, leading directly to clutch failure and codes like P0735.

Diagnosis Steps

1. Check the transmission fluid level and condition. Ensure it is full and does not appear dark, burnt, or contain excessive metal particles.
2. Use a professional-grade scan tool to check for any other transmission-related codes. Pay close attention to pressure switch or solenoid codes like P0868 or P0871, which often accompany P0735.
3. Record and analyze the Event Data or Freeze Frame data with the scan tool. This shows the conditions when the code was set, including line pressure vs. desired line pressure. A significant difference points to a hydraulic issue.
4. Check for any applicable Technical Service Bulletins (TSBs) or Recalls for your vehicle's VIN. Recall ZA3 addresses a heat/pressure issue that can cause fluid loss.
5. Perform a line pressure test to determine if the transmission's hydraulic pump is providing adequate pressure according to manufacturer specifications. Stock line pressure varies between 60-160 psi.
6. If pressure is low, drop the transmission oil pan and inspect for debris. A large amount of black, gritty material indicates a burned clutch pack, confirming internal failure.
7. If the pan is relatively clean, the issue likely lies within the valve body or solenoid pack. Test the solenoids and inspect the valve body for wear, especially the Solenoid Switch Valve (SSV) bore and accumulator plate.
8. Air check the clutch packs through the valve body ports with regulated shop air to listen for excessive leakage, which would indicate failed seals in the drum assembly.
9. If all hydraulic and electronic tests pass, the final step is to remove and disassemble the transmission to inspect the overdrive clutch pack directly.

Parts You'll Likely Need

• Transmission Solenoid Pack (OEM #68437849AA) — The solenoid pack is a common failure point on the 68RFE, causing pressure regulation issues that lead to clutch slip. For 2019+ models, this is often a 'blue plug' solenoid. This part number supersedes previous versions.
  Trusted brands: Mopar, Revmax, Suncoast
  OEM price range: $300-$450
  Aftermarket price range: $200-$350
• 68RFE Overdrive Clutch Rebuild Kit — If the overdrive clutches are burned (a high probability cause), a rebuild kit with new clutches, steels, and seals is required to repair the transmission. Aftermarket kits often offer higher clutch counts and more durable materials than stock.
  Trusted brands: Sonnax, Raybestos, Alto, Revmax
  OEM price range: $N/A
  Aftermarket price range: $300-$800
• Transmission Fluid and Filter Kit (OEM #68218058AC, 5013457AA) — This is required for any service that involves dropping the pan, such as replacing the solenoid pack or inspecting for debris. Use only Mopar ATF+4 fluid or a licensed equivalent to ensure proper performance and longevity.
  Trusted brands: Mopar
  OEM price range: $100-$180
  Aftermarket price range: $80-$150
• Upgraded Valve Body — Due to known wear issues in the stock valve body, many owners and shops opt to install a remanufactured and upgraded unit during a rebuild. These often feature oversized valves and other corrections to prevent future pressure loss.
  Trusted brands: Sonnax, Revmax, ATS Diesel, BD Diesel
  OEM price range: $N/A
  Aftermarket price range: $800-$1500

Related Codes That Often Appear With This One

• P0700 — This is a generic code indicating that the Transmission Control Module (TCM) has stored a fault. It acts as a 'check engine light' for the transmission system and will almost always be present with a specific transmission code like P0735.
• P0868 — This code indicates 'Transmission Fluid Pressure Low'. It often appears with P0735 because the clutch slippage is a direct result of insufficient hydraulic pressure to clamp the clutch pack. This points towards issues like a worn valve body, failing pump, or major internal leak.
• P0871 — This code indicates an issue with the Overdrive Pressure Switch Rationality. It points directly to a problem in the hydraulic circuit for the overdrive clutches, which are used for 5th gear. This code is a strong precursor to P0735, as it signals the pressure loss that will eventually cause the clutch to slip.
• P0736 — This code is for 'Gear 6 Incorrect Ratio'. Since the same overdrive clutch pack is used for both 5th and 6th gears, it is very common to see P0735 and P0736 appear together, indicating the entire OD clutch circuit has failed.

Technical Service Bulletins (TSBs) & Recalls

• ZA3 / NHTSA 22V-835: Addresses potential for transmission fluid to be expelled from the dipstick tube due to excessive heat and pressure, which can lead to low fluid levels and subsequent damage.
• NHTSA 19V-021: A recall related to the drag link assembly on 2013-2018 trucks, which can cause steering loss. While not directly related to the transmission, it's a critical safety issue for Ram HD trucks of this era.
• TSB 21-017-19 REV. A: A software update for the TCM on some Ram HD trucks to address various shift quality issues, such as harsh shifts, flares, and delayed engagements.

Platform-Specific Known Issues

• Safety Recall ZA3 / NHTSA 22V-835 was issued for 2020-2023 models with the 6.7L engine and 68RFE transmission due to a risk of heat and pressure buildup causing fluid to be expelled from the dipstick tube, creating a fire hazard. The remedy involves a new dipstick and vent assembly.

Mechanic-Grade Diagnostic Values

• Solenoid Coil Resistance (most solenoids) — expected: 1.3 Ohms. Failure: Readings significantly higher or lower than 1.3 Ohms, or an open circuit.
• Pressure Control Solenoid Coil Resistance — expected: 4.9 Ohms. Failure: Readings significantly higher or lower than 4.9 Ohms, or an open circuit.
• Stock Mainline Pressure — expected: Varies from 60 psi at idle/low load to 160 psi at high load. During shifts, it is preset to 150-160 psi.. Failure: Scan tool data showing actual line pressure is significantly below desired line pressure, especially under load, indicates a hydraulic leak, worn pump, or valve body issue.
• Clutch Volume Index (CVI) — expected: Low numerical value for a healthy clutch pack. Specific values vary by clutch.. Failure: A high CVI value indicates that the clutch pack is worn and has more tolerance, requiring more fluid volume to apply. This is a key indicator of internal wear.

Scan Tool Commands That Help

• wiTECH, Snap-On, Autel, or other professional scanner: Quick Learn — This procedure must be performed after replacing the transmission, valve body, or solenoid pack. It resets the transmission's adaptive memory and calibrates clutch fill times and volumes. Failure to perform a quick learn can lead to poor shifting and premature wear or damage to the new components.
• wiTECH or equivalent: Line Pressure Test — Used to compare the TCM's desired line pressure with the actual line pressure reported by the sensor. A significant discrepancy helps diagnose whether the issue is hydraulic (low actual pressure) or electronic.

Wiring & Ground Locations

• Transmission Solenoid / TRS Assembly Connector — On the driver's side of the transmission case, above the pan rail.. This is the main electrical connection for all solenoids. Pin 7 is the control for the Overdrive solenoid, and Pin 10 is the relay output that powers it. Testing for voltage and continuity at this connector is critical for diagnosing electrical faults causing the P0735 code.
• Line Pressure Sensor — On the passenger side of the transmission case.. This sensor provides the actual line pressure feedback to the TCM. If this sensor is faulty or its wiring is compromised, the TCM may receive incorrect data, leading to improper pressure control and clutch slippage. The signal circuit is pin T38 on the PCM C4 connector.

Real Owner Repair Stories

• Turbo Diesel Register forum user (Dodge Ram with 68RFE, 15k miles) — Check engine light on, transmission would not shift beyond 4th gear, either hot or cold.
  ❌ Tried (didn't work) Restarting the truck did not clear the issue.
  ✅ What actually fixed it The problem was a failed output speed sensor on the 68RFE. Replacing the sensor resolved the symptoms.

OEM Part Supersession History

• 68376695AA, 68353383AB (Gray/White Connector) → 68456067AA (Blue Connector) — Updated design for 2019+ model year vehicles.
  Heads up: The blue connector solenoid pack (68456067AA) is for 2019 and newer models only. Older trucks (2007.5-2018) use the white or gray connector packs. The packs are not interchangeable.

Model Year Variations Within This Range

• 2019-2024: Starting in 2019, the 68RFE valve body and solenoid pack were updated. The solenoid pack uses a different 'blue' connector (P/N 68456067AA) and the valve body features a Variable Force Solenoid (VFS) for the torque converter clutch that has a unique pressure/inductance curve. This makes parts like the solenoid pack incompatible with pre-2019 models.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Bosch CP4 High-Pressure Fuel Pump Failure 🔴 High — Common on 2019-2020 models. A failure can occur at any mileage and can destroy the entire fuel system. (Ref: Recall Y78 / NHTSA 21V880 was issued to replace the CP4 pump with a more robust CP3 pump.)
• Hydraulic Roller Lifter Failure 🔴 High — A known issue on 2019+ 6.7L Cummins engines. Ticking noises can start early, sometimes within 10,000 miles, and can lead to camshaft destruction and complete engine failure. (Ref: Ram issued a TSB advising against using 15W-40 oil in colder temperatures, as thicker oil may contribute to the problem.)
• Steering 'Death Wobble' 🟠 Medium — A persistent issue across many model years of Ram HD trucks, where hitting a bump at highway speeds can induce violent shaking in the front end. (Ref: Multiple recalls and TSBs have been issued for older generations (e.g., NHTSA 19V-021 for drag link welds), but the underlying geometry remains a point of concern for owners.)
• Electrical Shorts in Heater Relay 🔴 High — A recall was issued for an electrical short in a relay related to the intake air heater, which could lead to a vehicle fire, even with the engine off. (Ref: NHTSA recall identified for potential electrical shorts in diesel engine relays.)
• Popping/Cracking Noise from A-Pillar 🟡 Low — Affects some 2019+ trucks, causing a noise from the floor or A-pillar area during turns or body flex. (Ref: TSB 23-013-19 REV. A was issued to inspect and replace the A-Pillar body mounts to resolve the noise.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: Due to the high rate of internal wear on critical components like the valve body bores and accumulator pistons, sourcing used 'soft' parts for a 68RFE is generally not recommended. A used transmission case or other 'hard' parts from a verified low-mileage wreck could be considered, but core components related to hydraulic control should be purchased new or professionally remanufactured.

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 mileage and reason for being salvaged (e.g., collision damage vs. powertrain failure).
• If possible, inspect the transmission fluid from the donor vehicle. Any signs of dark, burnt fluid or metallic debris are major red flags.
• Check for any external damage to the transmission case, connectors, or sensors.

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

• Transmission Solenoid Pack: While aftermarket options exist, many reputable builders recommend using a new genuine Mopar solenoid pack to ensure compatibility and avoid issues with remanufactured units.

Aftermarket brands forum-validated for this vehicle:

• Valve Body / Components: Sonnax, Revmax, Suncoast, and Firepunk Diesel are highly regarded for their upgraded valve bodies and internal components that address the 68RFE's factory weaknesses like worn SSV bores and flexing accumulator plates.
• Rebuild Kits / Clutches: Sonnax, Revmax, and Suncoast offer comprehensive rebuild kits with higher quality clutches and steels designed to handle more power and heat than the OEM parts.

Brands owners have reported issues with on this vehicle:

• Unbranded or generic 'remanufactured' solenoid packs from online marketplaces are frequently cited as unreliable. Stick to new OEM or reputable transmission-specific brands.

Real Owner Stories

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

Related OBD-II Codes

• P0868 — Transmission Fluid Pressure Low. This code often accompanies P0735 because low hydraulic line pressure is a root cause of clutch slippage, which in turn causes the incorrect gear ratio error.
• P0871 — Overdrive Fluid Pressure Switch Rationality. This code points directly to a fault in the overdrive hydraulic circuit. It is often caused by the same valve body wear (SSV bore) that starves the overdrive clutch of pressure, leading to the slippage that triggers P0735.
• P0736 — Reverse Incorrect Gear Ratio. According to a cited transmission shop, this code and P0735 are often considered 'transmission out' codes, indicating a major internal failure like a burned clutch pack that requires removal and rebuilding of the transmission.

Frequently Asked Questions