P0755 on 2019-2020 Ram 3500: 2C Solenoid Circuit Causes and Fixes

What's Unique About the 2019-2020 Ram 3500

The 2019-2020 Ram 3500, equipped with the 68RFE transmission, has a well-documented history of issues with its integrated solenoid module (often called the solenoid pack). Failures are so common that Ram has issued multiple Technical Service Bulletins (TSBs) that address this specific code, often in conjunction with P0765 (UD Solenoid Circuit). TSB #9004380 even instructs dealers to collect diagnostic data before replacing the part, highlighting that the manufacturer is actively investigating the root cause of these failures. For 2019 and newer models, the solenoid pack is coded to the vehicle's ECM, meaning a replacement requires a specific relearn procedure with an advanced scan tool to input a 46-character code from the new solenoid.

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
• Harsh, erratic, or delayed shifting.
• Transmission stuck in 'limp mode' (usually 4th gear).
• Inability to shift into higher gears like 5th or 6th.
• Vehicle feels like it's slipping out of gear
• Shifting hangs between 5th and 6th gear, especially when using cruise control.

Most Likely Causes

1. Failed Transmission Solenoid Module (Solenoid Pack) 🔴 High Probability → Shop Transmission Assembly This is a well-documented weak point on the 68RFE transmission, as evidenced by multiple manufacturer TSBs. The entire module, which houses multiple solenoids, fails as a unit, often due to internal electrical faults or contamination.
   How to confirm: The presence of both P0755 and P0765 is a very strong indicator of a failed pack. A mechanic can use a scan tool to command the solenoid and check for a response or measure the electrical resistance of the 2C solenoid circuit at the transmission connector. The 2C solenoid control is located at Pin 20 of the main transmission connector. The expected resistance for the shift solenoids is typically around 1.3 Ohms. A reading that is significantly different, open, or shorted points to a bad solenoid pack.
   Typical fix: Replace the entire Transmission Solenoid/TRS Assembly. The updated Mopar part number is 68456067AB, which supersedes previous versions like 68456067AA and 68367309AA. It is critical to also replace both transmission filters (spin-on and sump) and refill with 7-9 quarts of Mopar ATF+4 fluid. A 'quick learn' procedure is required after installation.
   Est. part cost: $400-$700
2. Low or Contaminated Transmission Fluid 🟡 Medium Probability → Shop Transmission Assembly Heavy-duty trucks operate under high stress, which can accelerate the breakdown of transmission fluid. The 68RFE is known to be sensitive to fluid condition and level. Burnt or dirty fluid can cause solenoids to stick or fail.
   How to confirm: Check the transmission fluid dipstick. The fluid should be bright red and not have a burnt smell. Dark, brown, or metallic-flecked fluid indicates a problem and potential internal wear.
   Typical fix: Perform a transmission fluid and filter change using the correct Mopar ATF+4 fluid. If the fluid is heavily contaminated, a more thorough service may be required, but this may not fix an already failed solenoid pack.
   Est. part cost: $100-$200
3. Damaged Wiring or Connectors ⚪ Low Probability On some Ram HD trucks, the transmission wiring harness has been known to rub against the transmission dipstick tube bracket, which can wear through the wire insulation and cause a short circuit.
   How to confirm: Visually inspect the wiring harness leading to the main transmission connector for any signs of chafing, melting, or corrosion, paying close attention to the area around the dipstick tube bracket. Check for a poor connection at the main plug.
   Typical fix: Repair the damaged section of the wire and secure the harness away from the source of friction.
   Est. part cost: $10-$50

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is rare, but if the solenoid pack and wiring are confirmed to be good, the PCM's internal driver circuit for the solenoid could be at fault. This should be the last item to check. One owner on RamForum.com ultimately traced his P0755 to a bad computer after replacing the solenoid pack and servicing the valve body.
• Faulty Valve Body: → Shop Transmission Valve Body A warped or leaking valve body can cause hydraulic pressure issues that may trigger solenoid circuit codes. This is more likely on high-mileage or heavily used/tuned trucks. A Reddit user in r/Cummins noted that even after a warranty solenoid pack replacement, the P0755 code returned, and the consensus pointed to a leaking valve body as the underlying cause, a known weak point on tuned 68RFE transmissions.

Diagnosis Steps

1. Check the transmission fluid level and condition. Ensure it is full, clean, and does not smell burnt.
2. Use an OBD-II scanner to check for other related trouble codes, especially P0765, which strongly suggests solenoid pack failure.
3. Inspect the transmission wiring harness and main connector for any visible damage, corrosion, or loose connections. Pay special attention to the area where the harness may rub against the dipstick tube bracket.
4. If accessible, use a multimeter to test the resistance of the 2C solenoid circuit. At the transmission connector, test between Pin 20 (2C Solenoid Control) and Pin 10 (Power Feed). Compare the reading to the manufacturer's specification (typically around 1.3 Ohms for shift solenoids). An open circuit (infinite resistance) or shorted circuit (near zero resistance) points to a bad solenoid pack.
5. If the wiring and fluid are good, the most likely cause is the solenoid pack itself.
6. After replacing the solenoid pack, a transmission 'quick learn' or 'relearn' procedure must be performed with a capable scan tool. For 2019+ models, this involves scanning a barcode on the new solenoid to generate a 46-character code to enter into the PCM/TCM.

Parts You'll Likely Need

• Transmission Solenoid Module (Solenoid Pack) (OEM #68456067AB) — This is the most common failure point for a P0755 code on the 68RFE transmission. It is an integrated module containing multiple solenoids. Part number 68456067AB is the updated version, superseding 68456067AA and 68367309AA.
  Trusted brands: Mopar, RevMax, Sonnax, ATS Diesel
  OEM price range: $400-$700
  Aftermarket price range: $350-$600
• Transmission Filter Kit (Sump and Spin-on) — These should always be replaced when the transmission pan is removed to service the solenoid pack.
  Trusted brands: Mopar, Wix, Baldwin
  OEM price range: $50-$80
  Aftermarket price range: $30-$60
• Mopar ATF+4 Automatic Transmission Fluid — This is the required fluid type for the 68RFE transmission. A pan drop and solenoid replacement typically requires 7-9 quarts for refill. Using the correct fluid is critical for transmission health.
  Trusted brands: Mopar
  OEM price range: $10-$15 per quart

Related Codes That Often Appear With This One

• P0765 — This code is for the 'UD Solenoid Circuit'. Since both the 2C and UD solenoids are in the same module, a failure of the pack often triggers both codes. The TSBs from Ram frequently list these two codes together, making this combination a strong confirmation of solenoid pack failure.
• P0871 — This code for 'Transmission Fluid Pressure Sensor/Switch 'C' Circuit Performance' is also mentioned in TSB S2121000008RevC alongside P0755, indicating the solenoid pack failure can affect other integrated sensors within the same assembly.
• P0750 — This is a general code for 'Shift Solenoid 'A' Malfunction'. In some cases, multiple solenoid circuit codes can appear at once, pointing to a failure of the entire pack or a wiring/computer issue.

Technical Service Bulletins (TSBs) & Recalls

• 9004380: Requests event data download before solenoid module replacement for P0755/P0765 on 2020-2021 models.
• S2121000008RevC: Links DTCs P0755 (2C Solenoid Circuit), P0765 (UD Solenoid Circuit), and P0871 (Transmission Fluid Pressure Sensor/Switch 'C' Circuit).
• S2121000008: Links DTCs P0755 (2C Solenoid Circuit) and P0756 (UD Solenoid Circuit).

Platform-Specific Known Issues

• A recall was issued for 2019-2020 Ram 2500/3500 trucks for an issue where pressure and heat could cause a transmission fluid leak from the dipstick tube, creating a fire risk. The fix involved replacing the valve body separator plate and reprogramming the PCM. While not directly causing P0755, it highlights the stress these transmissions can be under.
• TSB #9004380 specifically requests that technicians download and send event data to Ram before replacing the solenoid module for a P0755 or P0765 code, confirming this is a known issue under active investigation by the manufacturer.
• TSB #S2121000008RevC and #S2121000008 explicitly link P0755 (2C Solenoid Circuit) with other solenoid and sensor codes like P0765 and P0871, pointing to the integrated solenoid/sensor assembly as the root cause.
• For 2019+ models, the solenoid pack is electronically married to the vehicle's computer. Replacement requires a special procedure using a scan tool to input a 46-character code generated from the new part to ensure proper function. Failure to do so will result in a non-operative transmission.

Mechanic-Grade Diagnostic Values

• 2C Shift Solenoid Coil Resistance — expected: ~1.3 Ohms. Failure: Open circuit (infinite resistance) or short circuit (near-zero resistance).
• General Shift Solenoid Coil Resistance — expected: 5 to 15 Ohms. Failure: A reading outside this range indicates a failed coil.
• (T219) 2C Solenoid Control Circuit Resistance to Ground — expected: Above 5.0 Ohms. Failure: Resistance below 5.0 Ohms indicates a short to ground in the wiring harness or solenoid pack.
• Solenoid Power Feed Voltage — expected: Battery Voltage (~12V). Failure: Low or no voltage at the solenoid power feed pin points to a wiring, relay, or PCM/TCM power supply issue, not the solenoid itself.

Scan Tool Commands That Help

• wiTECH, Autel, Snap-On, Launch: Quick Learn — This function is mandatory after replacing the transmission solenoid pack or valve body. It performs a clutch volume index (CVI) relearn, allowing the TCM to adapt to the new components. Failure to perform this can result in harsh shifting, damage to the new parts, and persistent codes.
• wiTECH or equivalent professional scanner: 2C Solenoid Actuation Test — This is a primary diagnostic step. The command attempts to activate the 2C solenoid. If the code P0755 returns immediately during or after the test, it confirms an electrical fault within the solenoid pack or its dedicated circuit, helping to rule out intermittent wiring issues.

Wiring & Ground Locations

• Transmission Main Connector (23-way) — On the left (driver's) side of the 68RFE transmission case. It is a large, round connector.. This is the primary point for testing the solenoid pack and wiring harness without removing the transmission pan. All solenoid control signals and power pass through this connector.
• Pin 20 (2C Solenoid Control) — At the 23-way main transmission connector.. This specific pin carries the control signal from the PCM/TCM to the 2C solenoid. It is the primary test point for checking resistance and shorts on the control side of the circuit. The circuit is often designated (T219) in service manuals.
• Pin 10 (Transmission Control Relay Output) — At the 23-way main transmission connector.. This pin supplies the main power feed to the entire solenoid pack. Testing between Pin 20 and Pin 10 can isolate the 2C solenoid coil for a resistance check.
• Transmission Ground Strap — A braided strap connecting the transmission case to the vehicle's chassis/frame, often near the transmission mount.. While not specific to the P0755 circuit, a poor main ground for the transmission can cause a host of bizarre electrical issues, including erratic solenoid behavior. Ensuring this connection is clean and tight is a fundamental electrical check.

Real Owner Repair Stories

• Reddit user in r/Cummins (2019 Ram 2500 with 6.7L Cummins, tuned and deleted, ~115k miles) — Went into limp mode while hauling, threw P0755 code.
  ❌ Tried (didn't work) A user in the same thread reported having the solenoid pack replaced under warranty, but the P0755 code returned.
  ✅ What actually fixed it The consensus from multiple users was that the underlying cause was a leaking/warped valve body, a known weak point on tuned 68RFE transmissions. One user with a similar issue on a 2016 model confirmed their fix was replacing the solenoid pack AND installing an upgraded BD Diesel valve body.
• Ram Heavy Duty Forum user (2021 Ram 2500 with 68RFE, 32,000 miles) — Cruise control kicked off, Check Engine Light on, transmission would not shift higher than 4th gear. Scanned and found 'shift solenoid B fault' (P0755).
  ❌ Tried (didn't work) Clearing the code (it came back within a few hundred miles for another user with the same issue).
  ✅ What actually fixed it The confirmed fix for a nearly identical truck was replacing the solenoid pack. The owner opted to also install an upgraded valve body from ATS Diesel at the same time as a preventative measure.
• YouTube video by 'Phillip Bailey' (2009 Ram 3500 with 68RFE (demonstrates a common wiring failure applicable to the 2019-2020 range)) — Stuck in 4th gear (limp mode) with code P0765 (UD Solenoid, often paired with P0755).
  ❌ Tried (didn't work) The video notes that many people replace the solenoid pack, but that did not fix the issue for him.
  ✅ What actually fixed it The problem was a chafed wire in the harness where it rubbed against the dipstick tube bracket. The insulation on the yellow wire with a light blue stripe had worn through. The final fix was repairing the damaged wire, which cost nothing in parts.

When the Usual Fixes Don't Work

• While the solenoid pack is the most common failure, it is not the only cause. In one documented case involving a tuned 2019 Ram, a warranty replacement of the solenoid pack did not fix the recurring P0755 code. The community consensus identified a warped valve body as the likely root cause, as it creates hydraulic leaks that the electrical systems cannot overcome. In another instance, a similar solenoid circuit code was traced to a simple chafed wire in the main harness, and repairing the wire resolved the problem completely without replacing the expensive solenoid pack. These cases show that diagnosing the wiring and considering the valve body's health, especially on modified trucks, is critical before defaulting to a solenoid replacement.

OEM Part Supersession History

• 68367309AA → 68456067AA — Manufacturer update for improved reliability or design change.
• 68456067AA → 68456067AB — Further revision and update by Mopar. This is the most current OEM part number.
  Heads up: 68456067AB is the correct direct replacement for 2019+ models. It is often identified as the 'blue connector' solenoid pack.

Model Year Variations Within This Range

• 2019+: Starting in 2019, the 68RFE uses a different solenoid pack (often called the 'blue connector' pack, P/N 68456067AB and its predecessors) than earlier models. Replacement of this pack requires a more involved 'Quick Learn' procedure where a barcode on the new part must be scanned to generate a character string that is programmed into the TCM/PCM.