P0765 on 2019-2020 Ram 3500: UD Solenoid Circuit Causes and Fixes

What's Unique About the 2019-2020 Ram 3500

For the 2019-2020 Ram 3500, particularly those with Cummins diesel engines and the 68RFE transmission, code P0765 is frequently linked to software issues rather than just hardware failure. Ram has issued multiple Technical Service Bulletins (TSBs), such as #18-093-22, where the prescribed fix for P0765 (often appearing with codes like P0299 Underboost and P0401 EGR) is a PCM/TCM software update. This indicates a logic error where the module may misinterpret sensor feedback. Another TSB (#9004380) requests that technicians download and send event data before replacing the solenoid module, suggesting the root cause can be complex and is often misdiagnosed as a simple part failure. For 2019 and newer models, the 68RFE uses an updated valve body and solenoid pack where the TCC solenoid has a unique calibration (PI Curve) that must be programmed to the vehicle with a scan tool upon replacement.

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 or other transmission warning light is on
• Transmission is stuck in one gear (limp mode), often 4th gear
• Harsh, delayed, or erratic shifting
• Inability to shift into higher gears (e.g., locked out of 5th and 6th)
• Reduced acceleration from a stop
• Engine no crank/no start (in some rare cases associated with a specific ECM issue)
• Driveline 'clunk' or 'bump' during gear shifts

Most Likely Causes

1. Powertrain/Transmission Control Module (PCM/TCM) Software Issue 🔴 High Probability → Shop Transmission Assembly Multiple TSBs (#18-005-23, #18-093-22) confirm that a software update is the specified fix, especially when P0765 appears with other DTCs like P0299 (Turbo Underboost) and P0401 (EGR Performance) on diesel models.
   How to confirm: Use a dealer-level scan tool (wiTECH) or contact a dealership/qualified shop to check if the vehicle's PCM/TCM software calibration is up to date against the latest available updates.
   Typical fix: Updating the PCM/TCM with the latest software calibration. This is a non-mechanical repair that reprograms the control module.
   Est. part cost: $0-$250
2. Faulty Transmission Solenoid / Solenoid Pack 🟡 Medium Probability → Shop Transmission Assembly The solenoid pack in the 68RFE is a known failure point. For 2019+ models, this is a single block assembly. The issue is so common that when P0765 appears with P0755 (2C Solenoid Circuit), a failed solenoid pack is the almost certain cause.
   How to confirm: After confirming software is updated and wiring is good, the solenoid itself can be tested. Using a multimeter, check the resistance of the solenoid coil at the transmission connector (for a 68RFE, the UD solenoid resistance should be around 1.3 ohms). A bidirectional scan tool can also command the solenoid on/off to check for a response.
   Typical fix: Replacing the entire transmission solenoid pack, which is located inside the transmission oil pan. For 2019+ models, this is a unit with a blue connector.
   Est. part cost: $300-$600
3. Wiring or Connector Issue 🟡 Medium Probability The wiring harness can be susceptible to damage from heat, vibration, or chafing against other components, such as the transmission dipstick tube bracket. This can cause an open or short in the circuit.
   How to confirm: Visually inspect the wiring harness between the TCM and the transmission case connector for any signs of damage, corrosion, or loose pins. Perform a continuity test on the UD solenoid control circuit (often the T59 circuit, a yellow wire with a light blue stripe) using a multimeter.
   Typical fix: Repairing the damaged section of wire or cleaning/replacing the affected connector. One owner fixed the code by finding and repairing a chafed wire, costing nothing in parts.
   Est. part cost: $10-$100
4. Low or Dirty Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly While P0765 is an electrical code, extremely low or contaminated fluid can cause a range of shifting problems, overheating, and sticking of mechanical parts within the solenoid, which may indirectly stress electrical components.
   How to confirm: Check the transmission fluid level and condition according to the manufacturer's procedure. The fluid should be at the correct level and not appear dark, burnt, or contain debris.
   Typical fix: Performing a transmission fluid and filter change using the correct Mopar-specified fluid (ATF+4 for the 68RFE).
   Est. part cost: $100-$250

Rare But Worth Checking

• Faulty Engine Control Module (ECM): A specific TSB for 2023 models (18-072-23 / RSU 23-160) notes that an internal ECM issue (capacitor leak) can cause P0765 along with a host of other codes and a no-start condition. While this TSB is for a slightly newer model year, it highlights a potential, though rare, cause.
• Intermittent Glitch: Some owners have reported that the P0765 code appeared once, caused limp mode, but was resolved by clearing the code with a scanner and did not return for thousands of miles. This suggests a potential one-time software or electrical hiccup.

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs). Given the history of this code on Ram trucks, this is the most critical first step. TSBs like 18-093-22 directly address this code.
2. Using a dealer-level scan tool (wiTECH), check for available PCM/TCM software updates. Apply any updates before proceeding.
3. Per TSB #9004380, if the fault is repeatable, a technician should download and save the event data *before* clearing codes or replacing parts to aid in root cause analysis.
4. Check the transmission fluid level and condition. Ensure it is clean, filled to the proper level, and does not smell burnt.
5. Inspect the transmission wiring harness and the main connector for any signs of physical damage, chafing, or corrosion. Pay close attention to areas where the harness may rub against brackets or the engine block.
6. Using a multimeter and wiring diagram, test the UD solenoid control circuit (T59 circuit, typically a yellow wire with a light blue stripe) for continuity, shorts to ground, and shorts to power between the TCM and the transmission connector.
7. If wiring and software are confirmed good, test the resistance of the solenoid at the transmission connector. Compare the reading to the OEM specification (approx. 1.3 Ohms for 68RFE). An open or out-of-spec reading indicates a failed solenoid.
8. If the solenoid resistance is out of spec or the circuit tests fail, the solenoid pack will likely need replacement. After replacement on a 2019+ model, perform the 'Program Torque Converter PI Curve' and 'Quick Learn' procedures.

Parts You'll Likely Need

• Transmission Solenoid Pack (OEM #68456067AB) — This is the most common hardware failure after software and wiring issues have been ruled out. For 2019+ 68RFE transmissions, this part has a blue connector. The original part number 68456067AA was superseded by 68456067AB.
  Trusted brands: Mopar
  OEM price range: $330-$600
  Aftermarket price range: $250-$450
• Transmission Fluid (OEM #68218057AC (Mopar ATF+4)) — Required when replacing the solenoid pack or servicing the transmission. The correct type (Mopar ATF+4 for the 68RFE) must be used to ensure proper operation.
  Trusted brands: Mopar
  OEM price range: $15-$25 per quart
  Aftermarket price range: $10-$20 per quart
• Transmission Pan Gasket (OEM #5013457AC (or part of filter kit)) — Must be replaced anytime the transmission pan is removed to access internal components like the solenoid pack. Often included with a new transmission filter.
  Trusted brands: Mopar, Fel-Pro
  OEM price range: $30-$50
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P0755 - 2C Solenoid Circuit — This code relates to another shift solenoid within the same solenoid pack. When P0755 and P0765 appear together, it strongly points to a common cause like a failed solenoid pack, a shared wiring issue, or a software fault mentioned in TSBs. [S2121000008RevC]
• P0871 - Transmission Fluid Pressure Sensor/Switch 'C' Circuit Performance — Linked with P0765 in TSB #S2121000008RevC, suggesting a related electrical or hydraulic issue within the transmission that the PCM is detecting simultaneously. This can also be caused by valve body cross-leaks.
• P0299 - Turbocharger Underboost / P0401 - EGR System Performance — The appearance of these engine codes with P0765 is noted in multiple TSBs (#18-093-22). This combination is a very strong indicator that the root cause is a PCM software logic error that requires an update to fix, not a mechanical transmission problem.

Technical Service Bulletins (TSBs) & Recalls

• 9004380: Mentions repeatable P0765 and requests event data download before swapping the solenoid module for root cause analysis.
• S2121000008RevC: Links P0765 (UD Solenoid Circuit) with P0871 and P0755.
• 18-005-23, 1802423, 18-093-22: TSBs that confirm a software update is the specified fix for P0765, often when it appears with other DTCs.

Platform-Specific Known Issues

• A significant number of TSBs exist for 2019-2023 models where P0765 is resolved by a PCM software update, especially on diesel models with the 68RFE transmission.
• TSB #9004380 specifically requests that technicians collect event data before replacing parts, indicating Chrysler is actively investigating the root cause of solenoid failures.
• The 2019+ 68RFE transmissions use a different solenoid pack (P/N 68456067AA, blue connector) than prior years, which used a white or grey connector.

Mechanic-Grade Diagnostic Values

• Underdrive (UD) Solenoid Coil Resistance — expected: ~1.3 Ohms. Failure: A reading of infinite resistance (open circuit) or a value significantly different from the specification indicates a failed solenoid coil.
• UD Solenoid Control Circuit (T59) Short to Ground Test — expected: Infinite resistance (O.L.). Failure: Any reading below 5.0 ohms indicates a short to ground in the wiring harness.
• UD Solenoid Control Circuit (T59) Continuity Test — expected: Less than 5.0 Ohms. Failure: A reading higher than 5.0 ohms indicates an open or high resistance in the circuit between the TCM and the transmission connector.

Scan Tool Commands That Help

• wiTECH (or equivalent OE-level scanner): Quick Learn — This procedure must be performed after replacing the valve body or solenoid pack. It resets transmission adaptive values and allows the TCM to learn the hydraulic and electrical characteristics of the new components.
• wiTECH (or equivalent OE-level scanner): Program Torque Converter PI Curve — This is a mandatory step for 2019+ models when the valve body or solenoid pack is replaced. The new TCC solenoid has a unique 46 or 66-digit calibration code (PI Curve) that must be programmed into the TCM for proper torque converter clutch operation.
• wiTECH (or equivalent OE-level scanner): Solenoid Actuation Test — This bidirectional command allows a technician to manually command the UD solenoid on and off to verify if the solenoid clicks and if the command from the TCM is being sent, helping to isolate a wiring, TCM, or solenoid issue.

Wiring & Ground Locations

• UD Solenoid Control Circuit (T59) — Yellow wire with a light blue stripe running between Pin 8 of the TCM C1 connector and Pin 17 of the main 23-pin transmission connector.. This is the specific wire that controls the Underdrive solenoid. It is the primary circuit to test for opens, shorts to ground, or shorts to power when diagnosing P0765. It is known to chafe on nearby brackets.
• TCM (Transmission Control Module) — Located on the passenger side of the engine bay, against the firewall.. This is the starting point of the T59 control circuit. The C1 connector (Pin 8) is where diagnostic tests for the circuit originate.
• Transmission Solenoid / TRS Assembly Connector — The main 23-pin round connector located on the driver's side of the 68RFE transmission case.. This is the termination point of the T59 circuit before it enters the solenoid pack. Pin 17 is the specific pin for the UD solenoid. The connector and its harness are common locations for damage, corrosion, or loose pins.

Real Owner Repair Stories

• YouTube channel 'Ovens Garage' (2009 Ram 3500 w/ 68RFE (demonstrates same fault logic and wiring as 2019-2020 models)) — Truck went into limp mode, stuck in 4th gear, with code P0765 (UD Solenoid control).
  ❌ Tried (didn't work) Owner was advised by forums to replace the solenoid pack or the TCM., Performed multimeter tests for circuit continuity, short to ground, and short to power, all of which passed, suggesting the wiring and solenoid were electrically sound.
  ✅ What actually fixed it A meticulous physical inspection of the wiring harness revealed that the T59 circuit wire (yellow with light blue stripe) had chafed through its insulation on a metal harness bracket, causing an intermittent short to ground. The wire was repaired with electrical tape and protected with loom, which resolved the code and limp mode permanently at no parts cost.

"I Checked Everything" — The Actual Cause

• While a smoke test is not applicable for this electrical fault, a similar pattern exists where standard electrical tests can be misleading. In a documented repair, the P0765 circuit passed all continuity and short-to-ground tests with a multimeter. The root cause was only found via a physical inspection of the harness, which revealed a chafed wire that was likely making intermittent contact with a ground bracket while driving, a condition not present when the vehicle was stationary for testing. This highlights that passing bench tests does not eliminate a wiring fault.

When the Usual Fixes Don't Work

• While common causes point to software updates or replacing the solenoid pack, there is strong evidence that these steps can be unnecessary expenses. A well-documented case showed that after passing all standard electrical tests, the true cause of P0765 was a simple chafed wire in the harness shorting to a bracket. This proves that a meticulous, hands-on physical inspection of the entire wiring harness from the TCM to the transmission is a critical, non-negotiable step before condemning a multi-hundred-dollar solenoid pack.

OEM Part Supersession History

• 68367309AA → 68456067AA — Part update/revision by manufacturer.
• 68456067AA → 68456067AB — Part update/revision by manufacturer.
  Heads up: The key identifier for 2019+ compatible parts is the blue electrical connector. Part number 68456067AA is listed for 2019+ models but has been superseded by 68456067AB.

Model Year Variations Within This Range

• 2019-2020: Compared to pre-2019 models, the 68RFE transmission features an updated valve body and solenoid pack. A critical difference is the use of a Variable Force Solenoid (VFS) for the torque converter clutch (TCC). When replacing the solenoid pack/valve body, the unique calibration data (PI Curve) for the TCC solenoid must be programmed into the TCM using a dealer-level scan tool. Failure to perform this step will result in torque converter clutch issues.