P0847 on 2016-2023 Mazda CX-9: Transmission Pressure Switch Causes and Fixes

What's Unique About the 2016-2023 Mazda CX-9

For the Mazda CX-9 and other models using the SKYACTIV-Drive 6-speed automatic transmission (FW6A-EL), P0847 is a well-documented issue. Mazda has released a series of TSBs over many years, with the latest being #05-002-23, which supersedes older ones like #05-003/20 and #05-002/15. The problem is rarely a wiring or sensor circuit failure, but rather a mechanical issue where metallic contamination in the transmission fluid causes the internal oil pressure switches to physically stick. This makes the diagnostic path very specific: update the software first, then replace the internal switches if the problem persists.

Symptoms You May Notice

• Check Engine Light and/or AT (Automatic Transaxle) warning light are on.
• Harsh or erratic shifting.
• Transmission gets stuck in one gear (often 3rd gear, known as 'limp mode').
• Delayed engagement when shifting from Park to Drive or Reverse.
• Reduced engine power as the TCM limits torque to protect the transmission.
• Other warning lights may appear, such as for the Traction Control System (TSC) or Smart City Brake Support (SCBS).

Most Likely Causes

1. Sticking Internal Oil Pressure Switches 🔴 High Probability → Shop Engine Oil Pressure Switch This is a known weak point in the FW6A-EL transmission. Mazda TSBs #05-002-23 and its predecessors state that contamination in the transmission fluid passage causes the oil pressure switches (A and B) on the control valve body to stick.
   How to confirm: This is confirmed by following the official Mazda TSB diagnostic procedure. If a TCM software update does not fix the code, the switches are deemed faulty and require replacement. The issue is strongly suspected if P0847 appears with related codes like P0842, P0872, P0877, or P0780.
   Typical fix: Replace the internal oil pressure switches (both Switch A and Switch B) located on the transmission's control valve body. This involves draining the fluid, removing the transmission pan, and replacing the switch assembly.
   Est. part cost: $100-$200
2. Outdated Transmission Control Module (TCM) Software 🟡 Medium Probability → Shop Transmission Assembly Mazda has released multiple software updates to improve the diagnostic logic for this specific issue and to better manage the transmission's hydraulic functions. In some cases, the updated software loosens the tolerances for the pressure sensor readings, preventing the code from triggering due to minor contamination.
   How to confirm: A Mazda dealership or a qualified independent shop with Mazda-specific tools (MDARS) can check the current software version and see if an update is available per the TSB.
   Typical fix: Reprogram the TCM to the latest calibration. This is the first step in the official repair procedure outlined in Mazda's TSBs. A Reddit user with a 2015 CX-5 fixed their P0847 and P0780 codes with this step alone for $170.
   Est. part cost: $0 (labor cost only)

Rare But Worth Checking

• Wiring Harness or Connector Issue: While the TSBs point to an internal mechanical issue, it is still possible for wiring damage or a corroded connector at the transmission to cause a circuit fault. This should be visually inspected before performing internal transmission work.
• Faulty Transmission Control Module (TCM): → Shop Transmission Assembly A failed TCM is very rare but possible. The official Mazda diagnostic procedure only points to TCM replacement after all other steps, including replacing the valve body, have failed. This should be the last resort.

Diagnosis Steps

1. Connect an OBD-II scanner and confirm the presence of P0847. Check for other related transmission codes (P0842, P0780, P1738, etc.).
2. Check the transmission fluid level and condition. Severely burned or dark fluid can indicate a larger problem, but the root cause is typically internal contamination causing the switch to stick.
3. Take the vehicle to a Mazda dealer or qualified shop to check the TCM software version against the latest version specified in TSB #05-002-23 or newer.
4. If the software is outdated, perform the TCM reprogramming as the first step.
5. Clear the codes and perform a road test. If code P0847 returns, the internal oil pressure switches are the confirmed cause.
6. Drain the transmission fluid and remove the transmission oil pan.
7. Visually inspect the fluid and pan magnet for excessive metal debris. If a large amount of foreign material is found, the oil strainer should also be replaced.
8. Following the service manual procedure, remove the control valve body to access and replace both oil pressure switches (A and B).
9. It is highly recommended to also replace the transmission filter (strainer) and oil pan gasket at this time.
10. Reinstall the valve body and oil pan, then refill the transmission with the correct Mazda FZ automatic transmission fluid.
11. Perform the 'Initial Learning' procedure with a diagnostic tool (like Mazda MDARS) as specified by Mazda. This step is mandatory.
12. Clear any remaining codes and perform a final road test to verify the repair.

Parts You'll Likely Need

• Transmission Oil Pressure Switch Kit (A & B) (OEM #FZ01-21-2C0) — This is the primary failure part identified in Mazda's TSBs for code P0847. The switches get stuck due to contamination and are replaced as a pair.
  Trusted brands: Mazda OE
  OEM price range: $100-$200
  Aftermarket price range: $80-$150
• Mazda FZ Automatic Transmission Fluid (OEM #0000-FZ-113E-01) — The transmission must be drained to perform the repair and refilled with the correct OEM-spec fluid. Using the wrong fluid can cause damage to SKYACTIV transmissions.
  Trusted brands: Mazda OE
  OEM price range: $20-$30 per quart
  Aftermarket price range: $15-$25 per quart
• Transmission Oil Pan Gasket (OEM #FW01-21-51X (example, verify by VIN)) — The gasket should always be replaced when the oil pan is removed to prevent leaks.
  Trusted brands: Mazda OE, Fel-Pro
  OEM price range: $30-$50
  Aftermarket price range: $20-$40
• Transmission Filter (Strainer) (OEM #FZ01-21-500) — It is best practice to replace the filter when the pan is off, especially since fluid contamination is the root cause of the switch failure. The TSB recommends replacement if significant debris is found in the pan.
  Trusted brands: Mazda OE, Wix, ATP
  OEM price range: $40-$60
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• P0842 — This code is for 'Oil pressure switch No. 1 (oil pressure switch B) stuck on'. Both switches are often replaced together as they are prone to the same contamination issue and are sold as a kit.
• P0780 — This code indicates a 'Gear shifting malfunction'. It's a general code that can be triggered by the specific pressure switch failure indicated by P0847.
• P0872 — This code is for 'Oil pressure switch No. 3 (oil pressure switch A) stuck on', another related pressure switch fault covered by the same TSBs.
• P0877 — This code is for 'Oil pressure switch No. 4 (oil pressure switch B) stuck on', another related pressure switch fault covered by the same TSBs.
• P1738 — A Mazda-specific code for 'Automatic transaxle internal malfunction' that is often triggered as part of the same event as the pressure switch codes.

Technical Service Bulletins (TSBs) & Recalls

• TSB #05-002-23: The most current TSB covering DTCs P0842, P0847, P0872, P0877, P0780, P1738. It identifies sticking oil pressure switches as the cause and outlines the reprogram/replace procedure.
• TSB #05-003/20: A widely superseded TSB, now incorporated into 05-002-23, that addressed the same sticking pressure switch issue.
• TSB #05-002/15: An older, superseded TSB that provided the initial diagnostic path of TCM reprogramming followed by parts replacement if the issue persists.

Mechanic-Grade Diagnostic Values

• Oil Pressure Switch A & B Bolt Torque — expected: 9—10 N·m {92—101 kgf·cm, 80—88 in·lbf}. Failure: N/A - This is an installation specification.
• Transmission Oil Pan Bolt Torque — expected: 8—10 N·m {82—101 kgf·cm, 71—88 in·lbf}. Failure: N/A - This is an installation specification.
• ATF Temperature for Initial Learning — expected: 40—110 °C {72—198 °F} or 60 to 110° C {140 to 230° F}. Failure: The initial learning procedure will abort or fail to start if the ATF temperature is outside this range.

Hidden / Shadow Codes Worth Checking

• P06B8:00: Internal Control Module Non-Volatile Random Access Memory (NVRAM) Error (see via This code may be stored in the TCM and is visible with the Mazda MDARS scan tool if the 'Initial Learning' procedure fails or is interrupted.)

Scan Tool Commands That Help

• Mazda MDARS (Mazda Diagnostic and Repair Software): Initial learning of AT — This is a mandatory procedure after replacing the oil pressure switches or the control valve body. It calibrates the TCM to the new components to ensure proper shift quality and prevent damage.
• Mazda MDARS: Module Reprogramming — This is the first step in the TSB diagnostic procedure to update the TCM software with improved logic for the pressure switch diagnostics.
• Manual Procedure (No Scan Tool): Manual Initial Learning/Shift Adapt Reset — A specific sequence of shifter movements and ignition cycles can be used to trigger the initial learning mode without a dealer scan tool. This is useful for DIYers or shops without MDARS to reset adaptations after fluid changes or minor repairs, though the MDARS method is officially required after component replacement.

Wiring & Ground Locations

• TCM/PCM Ground — A ground point for the Transaxle Control Module (TCM) and PCM is shared with the Data Link Connector 2.. While the cause of P0847 is almost always mechanical, a poor ground could theoretically cause erratic sensor readings. This is a very low probability cause but important for comprehensive diagnostics.
• Transmission Case Grounds — There are typically multiple grounds attached directly to the transmission case; one on top of the transmission and two on the front.. These grounds ensure the entire transmission assembly is properly grounded to the chassis. A loose or corroded ground here could affect various electronic components, though it is not a documented cause for P0847.
• Main Battery Ground Point — For jump-starting, Mazda specifies using a dedicated ground point on the chassis away from the battery, not the negative terminal itself.. This indicates Mazda's sensitivity to electrical system stability. Improper jump-starting could potentially damage sensitive modules like the TCM, although it's not a direct cause of this specific code.

Real Owner Repair Stories

• Reddit user in r/mazda (2015 Mazda CX-5 Touring, FWD, ~100k miles) — Check Engine Light and AT light came on, vehicle went into limp mode. Codes P0780 & P0847 were present.
  ✅ What actually fixed it The user took the vehicle to a Mazda dealer. The dealer performed the first step of TSB 05-002/15, which was to reprogram the TCM. This resolved the issue without needing to replace any parts. The cost was $170 for the diagnosis and reprogramming.
• Mazdas247 Forum user (2017 Mazda CX-5 Touring FWD, 120k miles) — Check Engine, AT, SBS, and TSC lights all came on simultaneously. After a restart, only the CEL remained. Code P0847 was stored.
  ❌ Tried (didn't work) The Mazda dealership quoted $8,000 for a new transmission, claiming that just replacing the switch would cause slippage due to contaminated fluid. The owner declined this repair.
  ✅ What actually fixed it The user's post is a request for guidance, but it highlights a common misdiagnosis. The community and TSB point towards replacing the pressure switches (Part FZ01-21-2C0) and performing a fluid service as the correct, much cheaper repair, rather than a full transmission replacement. The story is valuable for what to avoid.

OEM Part Supersession History

• fza1212c0 → FZ01-21-2C0 — Part number update/revision by Mazda. The parts are functionally identical.
  Heads up: The part numbers are interchangeable. FZ01-21-2C0 is the current part number to order.

Model Year Variations Within This Range

• 2016-2023: While the mechanical parts are the same, the required TCM software calibration file will vary by model year and vehicle configuration. The Mazda MDARS software automatically selects the correct file during the reprogramming procedure outlined in the TSBs.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Cracked Cylinder Head Causing Coolant Leak 🔴 High — Affects 2016-2020 models with the 2.5T engine built before June 9, 2020. Can occur well below 100,000 miles. The issue is caused by stress from the exhaust manifold leading to cracks in the cylinder head. (Ref: TSB 01-002/23 (supersedes 01-013/21). Mazda issued Customer Satisfaction Program (CSP11) extending the warranty for this specific issue to 10 years or 120,000 miles.)
• Excessive Oil Consumption Due to Faulty Valve Stem Seals 🟠 Medium — Primarily affects 2021 models with the 2.5T engine. Owners report the low engine oil light illuminating between scheduled oil changes. (Ref: TSB 01-003/23. A class action settlement resulted in an extended powertrain warranty for this issue, from 5 years/60k miles to 7 years/84k miles. The repair requires DTC P250F:00 to be present.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, using used parts is generally not recommended for the pressure switches themselves. However, a complete, low-mileage used valve body assembly from a reputable salvage yard could be a viable, cost-effective alternative to buying a new one if the entire unit is diagnosed as faulty, as it includes the switches and solenoids.

Donor-vehicle mileage cap: roughly under 60000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Verify the donor vehicle's VIN to ensure it did not have a history of transmission-related TSBs.
• Ask for a vehicle history report to check for accidents or flood damage.
• If possible, inspect the transmission fluid from the donor vehicle; it should be bright red and not smell burnt.
• Purchase from a seller that offers a warranty and a return policy.

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

• Transmission Oil Pressure Switch Kit (FZ01-21-2C0): Given the low cost of the new OEM part and the fact that contamination is the failure mode, installing a used switch is a significant risk for a negligible reward.
• Mazda FZ Automatic Transmission Fluid: The SKYACTIV-Drive transmission is highly sensitive to fluid type. Using anything other than genuine Mazda FZ fluid or a 100% compatible equivalent from a top-tier brand is not recommended.

Brands owners have reported issues with on this vehicle:

• Unknown/white-box online marketplace brands for the pressure switches. The quality control is unknown, and a failure requires re-doing the entire labor-intensive job.

Real Owner Stories

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

Related OBD-II Codes

• P0842 — Transmission Fluid Pressure Sensor/Switch 'A' Circuit Low. This code is frequently seen with P0847 and is caused by the same sticking internal oil pressure switch, as documented in Mazda TSB #05-002-23.
• P0780 — Shift Malfunction. This code often accompanies P0847 because the faulty pressure switch reading prevents the TCM from confirming a gear change correctly. It is addressed by the same TSB and repair procedure (TCM update or switch replacement).
• P0872 — Transmission Fluid Pressure Sensor/Switch 'C' Circuit Low. Like P0842 and P0847, this code is listed in Mazda's TSB as being triggered by the same root cause of contamination causing the internal pressure switches to stick.
• P0877 — Transmission Fluid Pressure Sensor/Switch 'D' Circuit Low. This is another pressure switch code covered by TSB #05-002-23, pointing to the same common failure of the pressure switch assembly on the valve body.
• P1738 — Automatic Transaxle Internal Malfunction. This more generic internal fault code is also included in the Mazda TSB for the sticking pressure switch issue, indicating it can be set as a result of the hydraulic pressure reading errors.
• P250F — Engine Oil Level Too Low. While unrelated to the transmission, this code is critical for diagnosing a separate known issue of excessive oil consumption on 2021 2.5T models. Its presence is required for the extended warranty repair per TSB 01-003/23.

Frequently Asked Questions