P0731 on 2018-2020 Ram PROMASTER: First Gear Incorrect Ratio Causes and Fixes

What's Unique About the 2018-2020 Ram PROMASTER

The Ram ProMaster in this year range uses the 62TE automatic transmission, a unit shared across many Chrysler, Dodge, and Ram vehicles. While generally reliable, this transmission is notoriously sensitive to fluid level and condition. A key specific for this platform is TSB #08-076-20, issued for 2018-2020 models, which indicates that a software update for the Anti-lock Brake System (ABS) module can resolve a MIL light for P0731 and other related codes. This suggests a potential logic issue in how the vehicle's modules interpret speed sensor data, rather than a purely mechanical fault. The solenoid pack is also a well-documented weak point on the 62TE. The 62TE itself is considered by some to be undersized for the heavy ProMaster chassis, leading to a higher rate of torque converter and internal component failure compared to its use in lighter minivan applications.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light is on.
• Transmission warning lamp may be illuminated.
• Vehicle enters "limp mode" (stuck in one gear).
• Harsh or delayed shifting, particularly into first gear.
• Slipping in first gear (engine RPMs rise but speed does not).
• Poor or slow acceleration from a stop.
• Increased fuel consumption.
• Vehicle feels sluggish or like it's dragging on acceleration.

Most Likely Causes

1. Low or Dirty Transmission Fluid 🔴 High Probability → Shop Transmission Assembly The 62TE transmission's performance is highly dependent on the correct fluid level and cleanliness to maintain proper hydraulic pressure for clutch and solenoid operation. Debris from normal wear or from excessive use of silicone sealant during a previous repair can clog filter screens and passages in the valve body.
   How to confirm: Check the transmission fluid level and condition using the dipstick (if equipped, some models have a capped tube). The fluid should be at the correct level, red in color (Mopar ATF+4), and not smell burnt. Dark, dirty, or low fluid indicates a problem.
   Typical fix: Perform a transmission fluid and filter change. 🎬 Watch: Step-by-step guide to changing your ProMaster fluid and filter. If the fluid is very low, the source of the leak must be found and repaired. If debris is suspected, dropping the pan for inspection is necessary.
   Est. part cost: $50-$150
2. Faulty Transmission Valve Body or Solenoid Pack 🔴 High Probability → Shop Transmission Valve Body The 62TE solenoid pack is a widely documented failure point. Solenoids control the flow of fluid to engage gears. Debris in the fluid can cause them to stick, or they can fail electronically, leading to incorrect hydraulic pressure and gear ratio errors.
   How to confirm: A professional technician will use a scan tool to monitor solenoid commands and pressures. Solenoids can also be tested for resistance at the 23-pin case connector. Often, this is diagnosed after a fluid change fails to resolve the issue.
   Typical fix: Replacement of the entire solenoid pack assembly, 🎬 See how to replace the 62TE solenoid pack yourself. which is mounted to the valve body. In some cases, the entire valve body assembly is replaced. A 'quick learn' or 'transmission adaptation' procedure with a capable scan tool is recommended after replacement.
   Est. part cost: $250-$700
3. Internal Transmission Mechanical Failure ⚪ Low Probability → Shop Transmission Assembly Includes issues like a worn-out underdrive clutch pack or a failing internal hydraulic pump. This is more common in higher-mileage vehicles or those subjected to heavy use, as the 62TE is considered undersized for the ProMaster's weight. A worn low clutch pack can result from prolonged operation with low hydraulic pressure.
   How to confirm: Diagnosed after all other possibilities are ruled out. Dropping the transmission pan and finding significant metal debris (beyond fine metallic dust on the magnet) is a strong indicator of internal failure.
   Typical fix: Requires a complete transmission rebuild or replacement.
   Est. part cost: $2000-$4500
4. Control Module Software Issue ⚪ Low Probability TSB 08-076-20 specifically calls out P0731 on 2018-2020 ProMaster models and lists the fix as reprogramming the ABS module with the latest software. This indicates a logic or communication error between modules can falsely trigger this code.
   How to confirm: A dealer or qualified shop with a wiTECH scan tool can check the current software calibration of the ABS module and compare it to the latest version available. If an update is available, this is a primary diagnostic step.
   Typical fix: Flashing/reprogramming the ABS module.
   Est. part cost: $0-$250 (labor for reprogramming)

Rare But Worth Checking

• Faulty Input/Output Speed Sensors: → Shop Automatic Transmission Speed Sensor While these sensors are used to calculate the gear ratio, they typically set their own specific trouble codes (like P0721) when they fail. However, an intermittent or failing sensor could potentially provide incorrect data, triggering P0731 without a dedicated sensor code. In one video diagnosis of a 2019 ProMaster, a loose turbine (input) speed sensor was found to be the root cause after live data showed it was not registering any RPMs.
🎬 Watch: Diagnosing a P0731 code and limp mode on a 2019 ProMaster.
• Faulty Powertrain Control Module (PCM) or Transmission Control Module (TCM): → Shop Transmission Assembly This is very rare. The control module should only be considered after all other mechanical and electrical possibilities have been exhaustively tested and ruled out.
• Incorrect Parts After a Rebuild: An ATSG bulletin notes that if a transmission was recently rebuilt, it's possible a rear planetary carrier from a 41TE transmission was used by mistake, which has a different tooth count for the sensor reluctor (24-tooth vs. the correct 48-tooth), causing gear ratio codes. Another possibility is swapping the Transfer Speed Sensor and Output Speed Sensor connectors, which are identical.
• Corrupted Adaptive Memory (VP Counters): The transmission stores adaptive learn values called CVI (Clutch Volume Index) or VP (Volume Ponds) counters. In some cases, particularly after a fluid change or other service, these values can become corrupted or 'timed out', forcing the transmission into limp mode even with no mechanical faults. A high-end scan tool is required to reset these counters.

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs). Specifically, for 2018-2020 models, check if TSB 08-076-20 (ABS module reprogram) applies and has been performed.
2. Check the transmission fluid level and condition. This is the simplest and most common cause. Ensure Mopar ATF+4 fluid is used.
3. Use an OBD-II scanner to check for any other transmission-related codes. Address any solenoid, pressure sensor, or speed sensor codes first.
4. With an advanced scan tool, monitor live data for transmission input (turbine), output, and transfer speed sensors to see if they are reading correctly while driving. A sensor that is not registering RPMs points to a sensor or wiring issue.
5. Inspect the transmission wiring harness and connectors, especially the main 23-pin connector to the transmission and the speed sensor connectors, for any visible damage, corrosion, or loose connections.
6. Inspect the primary transmission-to-chassis ground strap. On the ProMaster, this is a braided cable from the transmission case to the transmission mount, and it is a known point of failure. A poor ground can cause numerous electrical issues.
7. If fluid is low, top it off and re-test. If fluid is dirty or smells burnt, perform a transmission fluid and filter change. Inspect the pan magnet for excessive metal debris.
8. If the problem persists, perform resistance checks on the solenoid pack pins from the main transmission connector to test for open or shorted solenoids without removing the pan.
9. If pressures are low or solenoids are suspected based on resistance tests, the next logical step is the inspection and likely replacement of the solenoid pack.
10. If significant metal debris is found in the transmission pan, it indicates a severe internal mechanical failure requiring a rebuild or replacement.

Parts You'll Likely Need

• Transmission Fluid and Filter Kit (OEM #Filter Kit: 68018555AA, Fluid: 68218057AC (Mopar ATF+4)) — Low or contaminated fluid is a primary cause of shifting issues and this code. The filter is a common service item.
• Solenoid Pack / Valve Body Assembly — The solenoid pack is a very common failure point on the 62TE transmission, causing a wide range of shifting and pressure-related codes, including P0731.
• Input/Output Speed Sensors — Though less common to fail without their own codes, a faulty or loose speed sensor can directly cause a gear ratio error. They are often replaced in pairs.

Related Codes That Often Appear With This One

• P0732 — This is for 'Gear Ratio Error In 2nd'. It often appears with P0731 because the underlying hydraulic or mechanical issue (like low fluid or a bad solenoid) can affect multiple gears. [Bulletin #08-076-20, 10]
• P0868 — This code means 'Line Pressure Low'. Low hydraulic pressure is a primary cause of gear ratio errors, as it prevents clutches from engaging properly. [Bulletin #08-076-20, 10]
• P083B — 'LC Pressure Switch Rationality'. This, along with P0841, points to faults in the pressure switches that monitor the hydraulic circuits, which is directly related to the cause of P0731. [Bulletin #08-076-20, 10]
• P0841 — 'L/R Pressure Switch Rationality'. Similar to P083B, this indicates a problem in the transmission's hydraulic control system. [Bulletin #08-076-20, 10]
• P1790 — 'Fault Immediately After Shift'. This code can accompany gear ratio errors and often points towards an internal transmission problem or a fault detected during a shift attempt.

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #08-076-20: Mentions P0731 - Gear Ratio Error In 1st as a potential code found upon investigation of a check engine light on 2018-2020 models with the 3.6L engine and 62TE transmission. The fix is a software flash for the ABS module.
• ATSG Service Information 12-45: Not an OEM TSB, but an industry bulletin warning that P0731 can occur after a rebuild if incorrect parts (41TE planetary carrier) are used or if the speed sensor connectors are swapped.

Platform-Specific Known Issues

• A Technical Service Bulletin (TSB #08-076-20) was issued for 2018-2020 models for MIL illumination with P0731. The prescribed fix is to reprogram the ABS module with updated software, indicating a potential software logic issue.
• The 62TE transmission has a well-known vulnerability in its solenoid pack, making it a high-probability cause for this code across all vehicles that use this transmission.

Mechanic-Grade Diagnostic Values

• Solenoid Resistance (Low/Reverse, Underdrive, Overdrive, Direct, 2/4) — expected: 1.6 - 1.8 Ohms (approx. 2 Ohms). Failure: A reading that is significantly higher (e.g., 7+ Ohms), lower, or open (OL).
• Line Pressure Solenoid Resistance — expected: 4.8 - 5.1 Ohms. Failure: A reading outside this specific range.
• Pressure Switch Resistor Resistance — expected: ~300 Ohms. Failure: A reading significantly different from 300 Ohms.
• Input/Output Speed Sensor Resistance — expected: ~1590 Ohms (1.59 kOhms) at 72°F (22°C). Failure: A reading that is open (OL), shorted (near zero), or varies wildly. A faulty sensor may read 0.427 kOhms.
• Transfer Speed Sensor Resistance — expected: ~1424 Ohms (1.42 kOhms) at 72°F (22°C). Failure: A reading significantly outside the expected value.
• Valve Body Vacuum Test (Sonnax method) — expected: 15-20 "Hg for working valves, 25+ "Hg for check balls.. Failure: Low vacuum readings (closer to 5 "Hg) indicate a leak and wear in the valve body bores.

Scan Tool Commands That Help

• wiTECH, Autel, Snap-on, or equivalent professional scanner: Quick Learn / Transmission Adaptation — This procedure should be performed after replacing the valve body, solenoid pack, or entire transmission to allow the TCM to learn the new components' hydraulic characteristics.
• wiTECH, Snap-on, or equivalent high-end scanner: Reset VP Counters / Reset CVI (Clutch Volume Index) — Use when the vehicle is stuck in limp mode but no mechanical faults can be found. Corrupted adaptive data can 'time out' and lock the transmission in a fault state until it is manually reset.

Wiring & Ground Locations

• Transmission Ground Strap — A braided strap bolted from the transmission case to the top of the driver's side transmission mount. It is best accessed by removing the driver's side headlight assembly.. A poor or broken ground can cause erratic behavior from sensors and solenoids, leading to incorrect data being sent to the TCM and potentially triggering false gear ratio codes or other electrical faults.
• Solenoid Pack Connector (C1 / 23-way) — The main electrical connector on the front of the transmission case, connecting the vehicle harness to the solenoid pack.. This is the primary point for testing solenoid and sensor resistance without removing the transmission pan. Pin 10 is the common power feed for most solenoid tests.

Real Owner Repair Stories

• YouTube channel 'Dallas Auto Diag' (2019 Ram ProMaster) — Transmission stuck in limp mode, P0731 code present.
  ❌ Tried (didn't work) Initial code scan and review of service information.
  ✅ What actually fixed it While monitoring live data from all three speed sensors (input, transfer, output), it was observed that the Turbine (Input) Speed Sensor was not registering any RPMs when the vehicle was moved. The sensor itself was found to be loose in its bore. Securing the sensor resolved the issue.
• YouTube channel 'HumbleMechanic' (Ram ProMaster (year not specified)) — Transmission went into limp mode during a long trip.
  ❌ Tried (didn't work) The owner was considering towing to a dealership 100 miles away.
  ✅ What actually fixed it A mobile technician with a high-end Snap-on scanner was called. No parts were replaced. The technician accessed the transmission module and performed a function to 'reset all the counters in the VP' (Volume Ponds, also known as Clutch Volume Index or CVI). The transmission's adaptive learning had 'timed out,' forcing limp mode. Resetting the counters immediately took the van out of limp mode and restored normal operation.

Model Year Variations Within This Range

• 2018-2020: TSB 08-076-20 specifically applies to these model years, indicating that an ABS module software update can be a potential fix for P0731, suggesting a software logic issue that may not be present in earlier or later models.
• 2022+: Starting in model year 2022, Ram replaced the 62TE transmission in the ProMaster with a ZF 9-speed automatic transmission, which resolved many of the chronic issues associated with the 62TE in this heavy-duty application.