P0735 on 2019-2022 Ram 1500: Gear 5 Incorrect Ratio Causes and Fixes

What's Unique About the 2019-2022 Ram 1500

On the 5th generation (2019+) Ram 1500, which primarily uses the ZF 8-speed automatic transmission (models 8HP75 and 850RE), this code is frequently linked to software glitches. Ram has issued several Technical Service Bulletins (TSBs) to address shifting irregularities, including harshness and incorrect ratio codes, with software updates. TSB 21-033-20 specifically notes a software update to improve the 5-3-2 downshift to prevent P0735. While mechanical issues are possible, starting with a check for available TCM updates at a dealership is a platform-specific first step that often resolves the problem.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: The 2019-2022 model years primarily cover the 5th Generation Ram 1500 (DT platform). However, the 4th Generation 'Ram 1500 Classic' was also sold during these years. This guide focuses on the 5th Gen DT, which commonly uses the ZF 8-speed transmission (8HP75/850RE) where this code and its related TSBs are frequently documented.

Symptoms You May Notice

• Check Engine Light (MIL) is on.
• Harsh or rough upshifts and downshifts, particularly 'clunks'.
• Bumps or hesitation at low speeds, especially on light throttle application ('tip-in').
• Transmission may get stuck in one gear (limp mode).
• Delayed engagement or slipping when shifting into fifth gear.
• Poor fuel economy.
• Engine RPMs are higher than usual for a given speed when in 5th gear.

Most Likely Causes

1. Outdated Transmission Control Module (TCM) Software 🔴 High Probability → Shop Transmission Assembly Ram has released multiple software updates to fix shifting logic and prevent incorrect ratio codes. TSB #21-033-20 specifically includes an update to prevent P0735, and TSB #21-034-22 addresses P0735 accompanied by low-speed bumps and hesitation.
   How to confirm: A Ram dealership or a properly equipped independent shop using a tool like wiTECH can check for and apply available TCM software updates based on the vehicle's VIN.
   Typical fix: Reprogramming the TCM with the latest manufacturer software. This is a common first step at dealerships.
   Est. part cost: $0-$250
2. Low or Dirty Transmission Fluid 🔴 High Probability → Shop Transmission Assembly The ZF 8-speed transmission is sensitive to fluid level and condition. While marketed as 'lifetime' fluid, degradation can cause shifting issues. Low fluid levels starve the pump, reducing hydraulic pressure needed to hold clutches, causing slippage.
   How to confirm: Check the transmission fluid level and condition. This is a complex procedure on these sealed transmissions and must be done at a specific temperature (usually 30-50°C) with the engine running, via a fill plug on the side of the transmission.
   Typical fix: Perform a transmission fluid and filter service using the correct Mopar ZF 8&9 Speed ATF (Part #68218925AB) or an equivalent approved fluid like ZF LifeguardFluid 8. The filter is integrated into the transmission pan.
   Est. part cost: $150-$350
3. Faulty Transmission Valve Body or Solenoids 🟡 Medium Probability → Shop Transmission Valve Body The valve body directs hydraulic fluid to engage gears. Sticking solenoids or internal blockages can prevent proper hydraulic pressure from being applied to the 5th gear clutch pack, causing slippage. Forum users have reported this as a failure point.
   How to confirm: Requires advanced diagnostics, including pressure testing and solenoid function tests with a high-level scan tool. A technician may command individual solenoids to check for response.
   Typical fix: Replacement of the faulty solenoid pack or the entire valve body assembly. In one forum case, a valve body was replaced under warranty at 9,000 miles for a similar issue, though it did not solve the problem, leading to a full transmission replacement.
   Est. part cost: $600-$1500
4. Internal Transmission Mechanical Failure ⚪ Low Probability → Shop Transmission Assembly While less common than software or fluid issues, internal wear can occur, especially on trucks that are tuned or used for heavy towing. The failure is often within the clutch pack responsible for 5th gear (sometimes called the 'E' clutch in ZF diagrams), which can burn out from repeated slipping.
   How to confirm: Requires transmission disassembly and inspection of clutch packs (specifically the 5th gear clutch), drums, and seals. Burnt fluid is a strong indicator of this issue.
   Typical fix: Rebuilding or replacing the transmission.
   Est. part cost: $2500-$7000

Rare But Worth Checking

• Faulty Input/Output Speed Sensors: While a faulty speed sensor can cause ratio codes, it's less common for it to fail for only a single gear. Often, a failing sensor will trigger other specific sensor codes (like P0720) or affect multiple gears.
• Wiring Harness Issues: Damaged wiring or corroded connectors between the TCM and transmission sensors or solenoids can cause incorrect signals, leading to this code. This can be caused by chafing or contamination from fluid leaks.

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs) related to P0735 for your specific VIN. TSBs 21-034-22 and 21-033-20 are primary candidates.
2. Using a professional scan tool (like wiTECH), check for any available software updates for the Transmission Control Module (TCM) and Powertrain Control Module (PCM). Apply updates if available.
3. Scan for any other transmission-related DTCs. Address codes for speed sensors or pressure switches first.
4. Check the transmission fluid level and condition. This must be done according to the manufacturer's procedure, as these transmissions do not have a dipstick and the level is temperature-dependent (checked between 30-50°C).
5. If the fluid is low, top it off with Mopar 8&9 Speed ATF and check for leaks. If the fluid is dirty or smells burnt, perform a fluid and filter (pan) change.
6. If the code persists, perform a road test while monitoring live data from the input and output speed sensors to see if they are reading correctly and if the slippage in 5th gear is visible as a ratio mismatch.
7. If sensors and software are good, the next step is to inspect the transmission valve body and solenoids for proper function, checking for sticking valves or internal leaks.
8. If all other possibilities are exhausted, an internal inspection of the transmission for mechanical wear, such as a worn 5th gear clutch pack, is necessary.

Parts You'll Likely Need

• Transmission Fluid and Filter Kit (OEM #Fluid: 68218925AB; Pan/Filter: 68225344AA) — Low or contaminated fluid is a primary cause of shifting problems and incorrect ratio codes. The filter is integrated into the pan and must be replaced as a unit.
  Trusted brands: Mopar (ZF 8&9 Speed ATF), ZF LifeguardFluid 8
  OEM price range: $250-$400
  Aftermarket price range: $150-$300
• Transmission Valve Body Assembly — If software and fluid are good, a faulty valve body or solenoids are the next most likely mechanical cause, responsible for directing hydraulic pressure.
  Trusted brands: Mopar, ZF
  OEM price range: $1200-$1800
  Aftermarket price range: $800-$1400

Related Codes That Often Appear With This One

• P07E4-00 — Listed in TSBs #2100921 and #21-033-20 alongside P0735, indicating a related control module or internal transmission fault preventing Park engagement.
• P1DDE-00 — Mentioned in TSBs #2100921 and #21-033-20, suggesting a related electrical or ignition input issue that can occur with the transmission fault.
• P1DF3-00 — Appears with P0735 in TSBs #2100921 and #21-033-20, pointing to a potential ECU initialization error that accompanies the transmission problem.
• P0871 — This code for 'Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance' can accompany ratio error codes if a hydraulic pressure leak in the valve body is the root cause of the clutch slippage.

Technical Service Bulletins (TSBs) & Recalls

• 21-034-22: Addresses MIL illumination for P0735 and low-speed hesitation/bumps on 2022 models with the 5.7L eTorque.
• 0900321REVA: Lists P0735 with other codes related to clutch failure and fluid leaks.
• 2100921: Connects P0735 with drivetrain 'clunks' and harsh upshifts.
• 21-033-20: Details a software update specifically to improve shifting and prevent P0735 on 2019 models with the 3.6L engine.

Platform-Specific Known Issues

• TSB #21-034-22 was released for 2022 models to address a MIL for P0735 and customer complaints of 'Low speed tip in bumps/hesitation' and 'Low speed coast down bump in tow/haul mode', fixed with a TCM software update.
• TSB #21-033-20 explicitly includes a software enhancement to 'Improvement to the 5-3-2 downshift to prevent DTC P0735-00' for 2019 models with the 3.6L engine.
• Forum discussions on RamForum.com and 5thGenRams.com contain multiple owner accounts of experiencing incorrect gear ratio c

Mechanic-Grade Diagnostic Values

• Transmission Fluid Temperature for Quick Learn Procedure — expected: Must be at least 55°C (131°F) to begin the procedure.. Failure: The scan tool will not allow the Quick Learn or Static Adaptation (STADA) routine to start if the fluid is too cold. Adaptation learning will be aborted if the temperature exceeds 100°C (212°F).
• Line Pressure vs. Desired Line Pressure (from Event Data) — expected: The actual line pressure reading should be close to the desired line pressure reading.. Failure: If the line pressure reading is more than 10 psi below the desired reading, it indicates a potential issue with a plugged filter, main regulator valve in the pump, or excessive debris from clutch failure.

Hidden / Shadow Codes Worth Checking

• P1790 - Fault In Transmission Control Module: → Shop Transmission Assembly While not a hidden code itself, a diagnostic procedure for P0735 instructs technicians to check the scan tool's Event Data for P1790 with a 'Target Gear = 5th'. This indicates the TCM registered an internal fault specifically when trying to command 5th gear, which helps confirm the context of the P0735 code. (see via Using a professional scan tool to read the 'Event Data' or 'Freeze Frame' records associated with the P0735 fault.)

Scan Tool Commands That Help

• wiTECH or AlfaOBD: RESET ADAPTIVE VALUES — This procedure should be performed before the 'QUICK LEARN' routine. It clears the learned clutch application values from the TCM, which is necessary after component replacement or if trying to resolve shift quality issues.
• wiTECH or AlfaOBD: QUICK LEARN / STATIC ADAPTATION (STADA) — Used after replacing transmission components (like a valve body or entire unit) or to address customer shift quality concerns. The tool guides the technician through a series of steps to allow the TCM to relearn clutch fill times and pressures in a static, controlled environment.

Wiring & Ground Locations

• S109 — Located in the transmission harness, near the rear of the transmission by the post-catalytic temperature sensor take-off.. A corroded or damaged splice at this location could interrupt signals between the TCM and various transmission sensors or solenoids, potentially causing ratio codes.
• Power Distribution Center (PDC) — Under the hood.. The PDC houses fuses and relays critical for the powertrain and transmission control modules. A blown fuse or faulty relay (like the start/run relay) can cause a variety of electronic transmission faults.

Real Owner Repair Stories

• YouTube channel 'DIY Technician' (2010 Dodge Ram 1500) — Intermittent P0734 (Gear 4 Incorrect Ratio) and P0735 (Gear 5 Incorrect Ratio) check engine light codes. The truck would randomly get stuck in 4th gear.
  ❌ Tried (didn't work) Replaced the input and output speed sensors on the transmission., Replaced the transmission solenoid pack (valve body).
  ✅ What actually fixed it Replacing the Powertrain Control Module (PCM/ECM). The owner purchased a refurbished unit online, installed it, and the shifting problems and codes were resolved.

"I Checked Everything" — The Actual Cause

• In one documented case, an owner replaced the common culprits for P0735—the transmission speed sensors and the entire solenoid/valve body assembly—but the issue of getting stuck in gear with incorrect ratio codes persisted. The actual root cause was a failing Powertrain Control Module (PCM). This is a classic example of a problem appearing to be a mechanical or hydraulic transmission issue when it is actually an electronic control unit failure, which is often the last thing to be diagnosed due to its cost and complexity.

When the Usual Fixes Don't Work

• While TSBs and common knowledge point heavily towards software updates or internal transmission components (fluid, valve body) as the fix for P0735, there are owner-documented cases where the root cause was entirely external to the transmission. In one instance, after replacing both speed sensors and the solenoid pack to no avail, the final solution was replacing the Powertrain Control Module (PCM). This demonstrates that if standard transmission-focused repairs fail to resolve the code, diagnosis must be expanded to the primary electronic control units.

OEM Part Supersession History

• 68563804AA → 68563804AB — Part revision or update by manufacturer.
  Heads up: The new part (68563804AB) is specified for use on or after 04/09/21 for the 5.7L eTorque with the 8HP75 transmission.
• R8259301AA, R8259301AB → R8259301AC — Part revision for remanufactured valve body.
  Heads up: This part is listed for the Ram 1500 Classic with the 3.6L V6 and 845RE transmission, not the 5th Gen DT with the 8HP75.

Model Year Variations Within This Range

• 2022: For the 2022 model year, Ram introduced the Uconnect 5 infotainment system, which is faster and more customizable than the system in 2019-2021 models. This change affects the entire electronic architecture of the dashboard but is not directly linked to the transmission's mechanical operation.
• 2019-2021: The availability of certain diagnostic procedures may vary by software version. For example, on the related 845RE transmission, earlier model years required a TCM software update just to enable the 'Quick Learn' procedure, while later models had it available by default, indicating an evolution in the diagnostic capabilities of the TCM software.