P0751 on 2012-2013 Mazda 3: Shift Solenoid 'A' Causes and Fixes

What's Unique About the 2012-2013 Mazda MAZDA3 with 2.0L SkyActiv Engine & 6-Speed Automatic Transmission (FW6A-EL)

For the 2012-2013 Mazda 3 with the SkyActiv 6-speed automatic transmission (FW6A-EL) 🎬 Watch: A detailed technical overview of the Skyactiv FW6A-EL transmission., a P0751 code should be taken very seriously. It is critical to distinguish these models from those with the non-SkyActiv engines and 5-speed transmissions from the same years, as the TSBs apply specifically to the SkyActiv powertrain. Mazda has issued a series of Technical Service Bulletins (including #05-003-14-2898A and #05-005/13) indicating this code is a common symptom of a larger 'automatic transaxle internal malfunction'. The root cause is often contamination within the transmission fluid that causes internal oil pressure switches to stick, leading to a valve body malfunction. The fix prescribed by Mazda evolved from replacing the entire valve body to, in later bulletins, replacing only the affected pressure switches and sometimes reprogramming the TCM. An owner complaint documented this code appearing with a total loss of transmission power. [ODI #11596026] On this specific vehicle, the transmission control functions are integrated into the main Powertrain Control Module (PCM) located on the battery box, not a separate TCM on the transmission housing like in non-SkyActiv models.

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 and/or AT (Automatic Transmission) warning light is on. [ODI #11596026]
• Vehicle enters 'limp mode' (stuck in a single gear, usually 3rd).
• Harsh, abrupt, or 'clunking' shifts between gears.
• Delayed gear engagement or failure to shift.
• Car has no power to the transmission. [ODI #11596026]
• Reduced fuel economy due to inefficient gear selection.

Most Likely Causes

1. Internal Transmission/Valve Body Failure 🔴 High Probability → Shop Transmission Valve Body As noted in a series of TSBs (e.g., #05-003-14-2898A, #05-005/13), the SkyActiv 6-speed transmission is prone to contamination causing oil pressure switches on the valve body to stick. This is the most likely root cause when P0751 appears, especially if accompanied by P1738 or pressure switch codes (P0842, P0847, etc.).
   How to confirm: This requires professional diagnosis. A technician will follow the TSB diagnostic procedure, which involves checking for specific code combinations and potentially testing pressures. If other codes like P1738 are present, the diagnosis points directly to the valve body assembly.
   Typical fix: The fix can range from replacing the entire valve body assembly to the less-costly replacement of the specific oil pressure switches 🎬 See this walkthrough on replacing the oil pressure switches. (A and B) on the valve body, followed by an 'Initial Learning Procedure'. In some cases, a PCM software update is also required.
   Est. part cost: $800-$2500
2. Low or Dirty Transmission Fluid 🟡 Medium Probability → Shop Transmission Assembly Fluid is the lifeblood of the transmission. On this platform, degraded fluid carrying contaminants is the direct cause of the pressure switches sticking, which leads to the TSB-documented failure.
   How to confirm: Check the transmission fluid for level and condition. It should be bright red and not smell burnt. If it's dark, brown, or contains metallic particles, it's contaminated and has likely already caused internal issues. The ATF temperature should be 50°C (122°F) 🎬 Watch: How to correctly change and level your Skyactiv fluid. when checking the level.
   Typical fix: Perform a transmission fluid and filter change. Use fluid that meets Mazda FZ specification. However, if codes are already present, a fluid change alone is unlikely to fix the stuck components.
   Est. part cost: $50-$150
3. Failed Shift Solenoid 'A' ⚪ Low Probability → Shop Transmission Valve Body
   How to confirm: A mechanic can test the solenoid's resistance with a multimeter. For the FW6A-EL, Shift Solenoid #1 (A) is a normally closed linear solenoid and should have a resistance of 5-7 ohms. However, on this vehicle, this step can be misleading as the solenoid may be functional while the underlying valve body issue prevents it from working correctly.
   Typical fix: Replace the faulty shift solenoid. This requires draining the fluid and removing the transmission pan. This should only be done after ruling out the more common valve body issue.
   Est. part cost: $100-$200
4. Faulty Transmission Control Module (TCM) ⚪ Low Probability → Shop Transmission Assembly While PCM/TCM failure is possible, it is far less common than the mechanical/hydraulic issues described in the TSBs for this code. The control functions are integrated into the PCM on this model. Some TSBs do call for a PCM software update after valve body/switch repair.
   How to confirm: Diagnosed by a professional after ruling out all other possibilities. It often appears with communication codes like U0101.
   Typical fix: Repair or replace the PCM. The new or repaired unit will need to be programmed to the vehicle.
   Est. part cost: $300-$800

Rare But Worth Checking

• Damaged Wiring or Connectors: The wiring harness leading to the transmission can become damaged from heat, vibration, or road debris, causing a short or open circuit. Always inspect the harness between the PCM and transmission for visible damage before condemning internal components.

Diagnosis Steps

1. Check the transmission fluid level and condition. The ATF temperature should be at 50°C (122°F). If the fluid is low, dark, or smells burnt, this is a strong indicator of internal issues.
2. Use an OBD-II scanner to check for all other stored codes. The presence of P1738 or pressure switch codes (P0842, etc.) is critical for diagnosis on this vehicle.
3. Consult Mazda TSBs #05-003-14-2898A, #05-005/13, or later revisions. Follow the diagnostic flow chart provided by Mazda, which prioritizes the valve body/pressure switch issue.
4. Inspect the transmission wiring harness and connectors for any signs of damage, corrosion, or loose connections.
5. If diagnosis points to the valve body, the next step is to remove the transmission oil pan to access it.
6. Depending on the specific TSB procedure followed and diagnostic findings, either replace the entire valve body assembly or just the oil pressure switches 'A' and 'B'.
7. After component replacement, perform the 'Initial Learning Procedure' with a compatible scan tool (like Mazda M-MDS) as mandated by Mazda's repair instructions.

Parts You'll Likely Need

• Automatic Transmission Valve Body (OEM #PEY0-21-C00) — This is the most common point of failure according to Mazda TSBs for the P0751/P1738 code combination. Replacement is the most direct, though expensive, fix.
  Trusted brands: Mazda (Genuine OE)
  OEM price range: $1300-$1800
  Aftermarket price range: $800-$1200
• Automatic Transmission Oil Pressure Switch (A & B) (OEM #FZ01-21-2J0) — Later TSBs allow for the replacement of just these switches on the valve body, which are the components that actually stick due to contamination. This is a more targeted and less expensive repair.
  Trusted brands: Mazda (Genuine OE)
  OEM price range: $80-$110 (for one)
  Aftermarket price range: $100-$200
• Automatic Transmission Fluid (OEM #0000-FZ-113E-01) — Low or dirty fluid is a primary cause of solenoid issues and must be replaced during any internal transmission service. Only Mazda ATF-FZ fluid should be used.

Related Codes That Often Appear With This One

• P1738 — This Mazda-specific code for 'Automatic Transaxle Internal Malfunction' is the key indicator of the underlying issue. Mazda's diagnostic procedure for P0751 often starts by checking if P1738 is also present.
• P0780 — Indicates a general 'Shift Error'. It is listed alongside P0751 and P1738 in the TSBs as a related code. [ODI #11596026, 39]
• P0842, P0847, P0872, P0877 — These are codes for stuck oil pressure switches. Their presence strongly confirms the TSB-documented failure scenario where contamination is causing components on the valve body to stick.
• P0752, P0756, P0761, etc. — These are codes for other shift solenoids ('B', 'C', 'D', etc.). Their presence alongside P0751 strongly suggests a widespread issue like a failing valve body or PCM, not just one faulty solenoid.

Technical Service Bulletins (TSBs) & Recalls

• 05-003-14-2898A: Links P0751 with P1738 and other DTCs to an internal transaxle malfunction on 2012-2013 SkyActiv models.
• 05-005/13: Supersedes earlier bulletins, again linking P0780/P1738 and other codes (including P0751) to an internal issue and prescribing a valve body replacement.
• 05-002/15 & 05-005/14: Later revisions of the same issue, expanding the model years and detailing the cause as stuck oil pressure switches due to contamination. These bulletins introduce the repair option of replacing just the switches instead of the whole valve body.

Platform-Specific Known Issues

• Mazda Technical Service Bulletin #05-003-14-2898A and its successors explicitly link P0751 to an 'automatic transaxle internal malfunction' (P1738). The failure is not typically the solenoid itself, but rather contamination causing oil pressure switches within the valve body to stick.
• The 2012-2013 model years are a transition period. It is crucial to identify if the car has the 5-speed automatic or the 6-speed SkyActiv-Drive automatic, as this widespread issue is specific to the SkyActiv transmission.

Mechanic-Grade Diagnostic Values

• Shift Solenoid #1 (A) Resistance — expected: 5-7 ohms. Failure: Resistance outside of this range, or an open/short circuit.
• On/Off Solenoid Resistance — expected: 11-14 ohms. Failure: Resistance outside of this range. This is a different solenoid but provides context for testing.
• ATF Temperature for Level Check — expected: 50°C (122°F). Failure: Checking the fluid level when it is too hot or too cold will result in an inaccurate reading.

Hidden / Shadow Codes Worth Checking

• P06B8:00: Internal Control Module Non-Volatile Random Access Memory (NVRAM) Error (see via This code is displayed on the Mazda M-MDS scanner if the 'Initial Learning' procedure has not been implemented after replacing the control valve body or oil pressure switches.)

Scan Tool Commands That Help

• Mazda M-MDS (or equivalent high-end scanner): Initial Learning Procedure — This is a mandatory procedure after replacing the control valve body, oil pressure switches, clutches, or the entire automatic transaxle. Failure to perform it can result in engine racing or increased shift shock.
• Mazda M-MDS (or equivalent high-end scanner): Module Reprogramming — For some 2012-2013 Mazda3 vehicles within a specific VIN range (ending before 733727), a TCM (PCM) reprogram to the latest software version is required after valve body replacement to improve diagnostic logic.

Wiring & Ground Locations

• PCM (Powertrain Control Module) — On the 2012-2013 SkyActiv models, the transmission control functions are integrated into the PCM. This module is mounted directly to the battery box in the engine compartment, not on the transmission housing itself.. Technicians accustomed to finding a separate Transmission Control Module (TCM) on the transmission of non-SkyActiv Mazdas will be looking in the wrong place. All electrical testing for transmission commands must be done at the PCM connectors on the battery box.
• Main Transmission Connector — On the top or side of the FW6A-EL transmission housing, below the battery and air intake assembly.. This is the primary connection point between the PCM and all internal transmission electronics, including the shift solenoids and pressure switches. It's a key location for testing wiring continuity and solenoid resistance without dropping the transmission pan.

OEM Part Supersession History

• FZA1-21-2J0 → FZ01-21-2J0 — Part number update or revision by the manufacturer.
  Heads up: FZ01-21-2J0 is the current part number for the 'B' oil pressure switch, which is one of the two switches often replaced to fix this issue.
• PEY0-21-C00B → PEY0-21-C00C — Part number update or revision for the valve body assembly.

Model Year Variations Within This Range

• 2012-2013: The 2012 model year was the first to introduce the SkyActiv powertrain (2.0L direct-injection engine and 6-speed automatic FW6A-EL) to the Mazda3 platform. Earlier second-generation models (2010-2011) used the MZR engine with a 5-speed automatic, which has a different TCM location and is not subject to the same TSBs regarding P0751. There were minor infotainment and trim changes between 2012 and 2013, but the powertrain and the P0751 issue are identical.