P0751 on 2005-2023 Chrysler 300: Shift Solenoid 'A' Causes and Fixes

What's Unique About the 2005-2023 Chrysler 300

The Chrysler 300's long production run from 2005 to 2023 means this code has two very different primary causes depending on the transmission. First-generation models (and some early second-gen V8s) use the 5-speed Mercedes-designed NAG1 (W5A580) transmission, where electronic faults are very commonly traced to a failing conductor plate. This plate is a known weak point, housing the solenoids and speed sensors, and often fails due to heat and age. Later second-generation models use the 8-speed ZF-designed 845RE transmission, where diagnosis often starts with a software update before condemning the integrated valve body/solenoid assembly (mechatronic unit).

Generation note: This guide covers two main generations and their associated transmissions: - 2005-2014 (Primarily 1st Gen LX & early 2nd Gen LD with V8): These models are often equipped with the 5-speed NAG1/W5A580 automatic transmission. The most common failure point is the conductor plate, which contains the speed sensors and solenoid connections. - 2012-2023 (Primarily 2nd Gen LD): These models typically have the 8-speed 845RE automatic transmission. Diagnosis for these often starts with software updates, followed by potential valve body replacement, as the solenoids are integrated.

Symptoms You May Notice

• Transmission is stuck in one gear (limp mode), usually 2nd gear.
• Harsh, delayed, or failed shifts.
• Check Engine Light is illuminated.
• Transmission slipping, where engine RPMs flare up without acceleration.
• Reduced fuel economy.
• Inability to shift into higher gears.
• Vehicle may feel sluggish or underpowered.

Most Likely Causes

1. Low or Dirty Transmission Fluid 🔴 High Probability → Shop Transmission Assembly Fluid is the lifeblood of the transmission. Over time it degrades or can leak, causing pressure issues that prevent solenoids from actuating correctly. Contaminated fluid can clog the small passages in the valve body and solenoids.
   How to confirm: Check the transmission fluid level and condition. On NAG1 transmissions, this requires a special service dipstick tool. The fluid should be bright red and not smell burnt. On 845RE transmissions, it's a sealed unit checked via a fill plug at a specific temperature.
   Typical fix: Perform a transmission fluid and filter change using the correct OEM-specified fluid (e.g., Mopar ATF+4 for NAG1, Mopar ZF 8&9 Speed ATF for 845 🎬 See this step-by-step ZF 845RE transmission service walkthrough.RE).
   Est. part cost: $80-$200
2. Failed Conductor Plate (5-Speed NAG1/W5A580 Models) 🔴 High Probability The conductor plate, which houses speed sensors and electrical pathways, is a very common failure point on the NAG1 transmission due to heat and age, leading to various electronic faults. The integrated speed sensors are often the first components to fail.
   How to confirm: Diagnosis typically involves testing the electrical signals at the transmission connector or TCM connector. Fault codes for speed sensors (P0716, P2767) often accompany solenoid codes when the conductor plate is the root cause. A technician can test resistance between pins at the TCM connector to verify the integrity of the solenoids and wiring. 🎬 Watch: How to test the conductor plate and solenoids remotely.
   Typical fix: Replace the conductor plate, transmission filter, pan gasket, and the electrical connector plug sleeve (a common leak point).
   Est. part cost: $150-$300
3. Outdated TCM Software (8-Speed 845RE Models) 🟡 Medium Probability The 8-speed transmission's shift logic is complex and heavily software-dependent. Chrysler has released numerous software updates (TSBs) to improve shift quality and resolve erroneous diagnostic trouble codes.
   How to confirm: A dealership or a well-equipped independent shop must use a diagnostic tool like wiTECH to check the current software version against the latest available from Chrysler. TSBs like 21-004-15 and 21-003-15 address shift enhancements.
   Typical fix: Reprogram (flash) the Transmission Control Module (TCM) to the latest software version.
   Est. part cost: $0-$250 (labor cost)
4. Failed Valve Body / Solenoid Assembly (8-Speed 845RE Models) 🟡 Medium Probability → Shop Transmission Valve Body On the 845RE, the shift solenoids are integrated into the valve body (mechatronic unit). A mechanical failure of a single solenoid or a blockage within the valve body requires replacement of the entire assembly.
   How to confirm: If a TCM software update does not resolve the issue and the fluid/wiring is confirmed to be good, the valve body is the next likely culprit. A technician can command the solenoid with a scan tool to check for response.
   Typical fix: Replace the entire transmission valve body assembly.
   Est. part cost: $800-$2000

Rare But Worth Checking

• Faulty Transmission Control Module (TCM): → Shop Transmission Assembly While rare, the TCM itself can fail, leading to an inability to command the solenoid correctly. This is usually suspected only after all other possibilities, including wiring, solenoids, and fluid, have been ruled out.
• Damaged Wiring Harness: The wiring harness leading to the transmission can be damaged by road debris or engine heat, causing a short or open circuit. A visual inspection and continuity tests from the TCM connector are the first steps in checking for this.

Diagnosis Steps

1. Check transmission fluid level and condition. This is the first and most important step.
2. Scan for other transmission-related codes. P0700 is expected. Look for speed sensor codes on NAG1 models.
3. For 8-Speed 845RE models: Check for available TCM software updates using a capable scan tool (like wiTECH) and flash if a newer version is available.
4. Inspect the transmission's main electrical connector for corrosion, damage, or fluid intrusion (especially on NAG1 models).
5. For 5-Speed NAG1 models: Test the resistance of the shift solenoid circuits from the TCM connector. For Shift Solenoid 'A' (1-2/4-5), check for 2.5-4.5 Ohms between Pin 14 and Pin 38 of the C2 connector. An out-of-spec reading suggests a wiring or conductor plate issue.
6. Drop the transmission pan and inspect for excessive metal debris, which would indicate a severe internal mechanical failure.
7. For 5-Speed NAG1 models: If electrical tests point to an internal fault, replace the conductor plate, filter, and connector sleeve.
8. For 8-Speed 845RE models: If software is up-to-date, use a bidirectional scan tool to command Shift Solenoid 'A' on and off to check for an audible click and response. If it fails, the valve body assembly is likely faulty.
9. If a solenoid or conductor plate is replaced, perform a transmission relearn procedure as specified by the manufacturer.

Parts You'll Likely Need

• Transmission Conductor Plate (NAG1/W5A580) (OEM #52108308AC) — This is the most common point of electronic failure in the 5-speed NAG1 transmission, causing a wide range of shifting problems and codes.
  Trusted brands: Mopar, Dorman, Standard Motor Products
  OEM price range: $200-$300
  Aftermarket price range: $120-$200
• Transmission Valve Body Assembly (845RE) (OEM #68233747AA) — For the 8-speed transmission, solenoids are integrated into this unit. If a solenoid fails mechanically, the entire assembly must be replaced.
  Trusted brands: Mopar
  OEM price range: $800-$2000
  Aftermarket price range: N/A
• Transmission Filter and Pan Gasket Kit — This should be replaced any time the transmission pan is removed for service.
  Trusted brands: Mopar, ATP, Wix
  OEM price range: $50-$80
  Aftermarket price range: $25-$50
• Transmission Electrical Connector Plug (NAG1/W5A580) (OEM #68021352AA) — This connector sleeve is a notorious source of fluid leaks on the NAG1 transmission and should always be replaced when servicing the conductor plate or valve body.

Related Codes That Often Appear With This One

• P0700 — This is a generic code that simply means the Transmission Control Module (TCM) has stored a fault. It will almost always be present alongside a more specific transmission code like P0751.
• P0716, P2767 — These codes relate to the input/turbine speed sensors. On the NAG1 transmission, these sensors are integrated into the conductor plate. Seeing these codes with P0751 strongly points to a failed conductor plate.

Technical Service Bulletins (TSBs) & Recalls

• 21-004-15 — Flash: 845RE Transmission Shift Enh

Mechanic-Grade Diagnostic Values

• NAG1 Shift Solenoid 'A' (1-2/4-5) Resistance — expected: 2.5 - 4.5 Ohms. Failure: A reading of infinite resistance (OL) indicates an open circuit, while a reading near zero indicates a short. Either will condemn the circuit.
• NAG1 Other Solenoid Resistances (for comparison) — expected: 2-3 Solenoid: 2.5-4.5 Ohms; 3-4 Solenoid: 2.5-4.5 Ohms; TCC Solenoid: 2.5-4.5 Ohms; Modulation Pressure Solenoid: 4.0-6.0 Ohms; Shift Pressure Solenoid: 4.0-6.0 Ohms. Failure: Values outside of these ranges when tested at the TCM connector point to a wiring or conductor plate issue.
• TCM Power Supply Voltage — expected: Approximately 12.6V (Battery Voltage). Failure: Voltage drop greater than 0.5V indicates high resistance in the power or ground circuit.

Scan Tool Commands That Help

• wiTECH (Chrysler Dealer Tool) or equivalent professional scanner: Reset Adaptive Values — This should be performed after replacing a valve body or conductor plate to clear the learned shift adaptations, forcing the TCM to relearn.
• wiTECH (Chrysler Dealer Tool) or equivalent professional scanner: Quick Learn — For 8-speed 845RE transmissions, this procedure is required to match the TCM's electrical system with the solenoids in a new valve body. It should be performed after replacing the valve body or TCM. TSB 21-013-13 details when this procedure is necessary.
• wiTECH (Chrysler Dealer Tool) or equivalent professional scanner: Solenoid Actuation Test — A bidirectional command to manually activate and deactivate Shift Solenoid 'A'. This helps determine if the solenoid is mechanically stuck or if the electrical circuit is faulty. The technician should listen for an audible click from the transmission pan area.

Wiring & Ground Locations

• NAG1 Transmission Control Module (TCM) — Located under the driver's side of the instrument panel, accessible by removing the lower kick panel.. This is the primary location for testing solenoid and sensor circuits without having to access the transmission itself. All circuit resistance checks can be performed at its C1 and C2 connectors.
• NAG1 TCM C2 Connector — The 38-pin connector at the TCM under the driver's side dash.. This connector contains the pins for the shift solenoids. Specifically, the 1-2/4-5 Shift Solenoid ('A') circuit is on Pin 14 (control) and Pin 38 (solenoid supply voltage).
• TCM Ground Circuit (Z910/Z912) — The ground circuit for the TCM, which typically grounds to the chassis near the module's location under the dash.. A high-resistance or open ground circuit can cause the TCM to operate incorrectly, potentially setting false solenoid codes. This circuit should be checked for integrity if other electrical tests are inconclusive.

Real Owner Repair Stories

• ChargerForums user (2009 Dodge Charger Police Package (NAG1 Transmission)) — Harsh 1st to 2nd gear shift, check engine light.
  ❌ Tried (didn't work) Initial diagnosis pointed towards a solenoid issue.
  ✅ What actually fixed it Replacing the conductor plate with a Dorman aftermarket unit (917-678) resolved the shifting issue.
• Jeep Wrangler JK Forum user (shared NAG1 platform) (2012 Jeep Wrangler (NAG1 Transmission)) — Lack of transmission engagement, limp mode.
  ❌ Tried (didn't work) Testing individual solenoids, which appeared to be within spec.
  ✅ What actually fixed it The final fix was replacing the entire conductor plate, which houses the integrated speed sensors that were the likely root cause of the failure.

OEM Part Supersession History

• 52108308AB → 52108308AC — Standard part revision by the manufacturer, likely for improved durability or minor design changes.
  Heads up: The parts are interchangeable; 52108308AC is the current replacement for the older AB version.

Model Year Variations Within This Range

• 2012-2014 (845RE): Early models with the 8-speed 845RE transmission are more susceptible to software-related shifting issues. TSBs like 21-013-13 and 21-018-14 were released to address these concerns by reprogramming the TCM. Later models often came with this updated software from the factory.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Shifter Stuck in Park ('Pink Thingy' Failure) 🔴 High — Very common on 2005-2007 models with the 5-speed NAG1 transmission. A small plastic interlock latch inside the shifter assembly breaks, immobilizing the vehicle.
• Front Suspension Clunk/Rattle 🟠 Medium — Common across all model years. Often caused by worn sway bar links, sway bar bushings, or tension struts, leading to clunking noises over bumps.
• 5.7L HEMI 'Tick' (MDS Lifter Failure) 🔴 High — Affects 2009 and newer models with the 5.7L HEMI V8. A ticking noise is an early symptom of a failing MDS (Multi-Displacement System) lifter, which can lead to camshaft damage and costly engine repairs if ignored.
• Uconnect 8.4-inch Screen Delamination 🟠 Medium — Common on 2017 and newer models. The screen's adhesive fails, causing bubbling and 'ghost touches' that make the infotainment system erratic and difficult to use.
• Early 2.7L V6 Engine Oil Sludge 🔴 High — A notorious problem for early first-generation models (2005-2010) equipped with the 2.7L V6. Internal design flaws can lead to oil sludge buildup, causing engine failure if not meticulously maintained with frequent, high-quality oil changes.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For the expensive 8-speed (845RE) valve body assembly, a used part from a low-mileage, verified-running donor vehicle can be a cost-effective alternative to a new OEM unit, which can cost over $1,500. A used TCM can also be an option, but will require programming to the vehicle's VIN.

Donor-vehicle mileage cap: roughly under 75000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a valve body, ask for the donor vehicle's VIN to check its service history.
• Ensure the part comes from a vehicle that was not involved in a severe collision.
• Inspect the electrical connectors for any signs of corrosion, bent pins, or damage.
• If possible, get a short-term warranty from the salvage yard.

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

• For the 8-speed (845RE) valve body, Mopar (OEM) is the only reliable source for a new part. Aftermarket options are generally not available or trusted for this complex component.

Aftermarket brands forum-validated for this vehicle:

• Dorman and Standard Motor Products (SMP) are widely used and generally accepted aftermarket brands for the 5-speed NAG1 conductor plate.

Brands owners have reported issues with on this vehicle:

• Some users have reported fitment issues with certain Dorman conductor plates for the NAG1, occasionally requiring minor modification to install. Unbranded, low-cost conductor plates and valve bodies from online marketplaces should be avoided due to high failure rates.

Real Owner Stories

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

Related OBD-II Codes

• P0700 — An informational code indicating the Transmission Control Module (TCM) has requested Check Engine Light illumination; it almost always accompanies P0751.
• P0716 — An input speed sensor circuit range/performance code that often appears alongside P0751 when the conductor plate fails on NAG1 transmissions.
• P2767 — An input speed sensor 2 circuit no signal code, frequently seen with P0751 as a symptom of a failing NAG1 conductor plate.

Frequently Asked Questions