P0847 on 2014-2017 Mazda MAZDA6: Transmission Pressure Switch Fault Causes and Fixes

What's Unique About the 2014-2017 Mazda MAZDA6

This is a well-documented issue on Mazda's Skyactiv-Drive 6-speed automatic transmissions (model FW6A-EL) used in this generation of MAZDA6, as well as the Mazda3 and CX-5. The problem is so recognized that Mazda has released multiple TSBs. Unlike many vehicles where this code points to a wiring problem or a simple sensor failure, on this platform, the cause is most often the physical switch mechanism getting stuck due to microscopic contamination within the transmission fluid, leading to a specific set of related trouble codes. One owner on Mazdas247.com noted that the TCM software update is designed to loosen the pressure sensor tolerances to prevent the code from triggering due to minor contamination with age.

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
• Automatic Transaxle (AT) warning light is on
• Harsh or erratic shifting
• Transmission may get stuck in one gear (limp mode)
• Delayed engagement when shifting into Drive or Reverse
• In some cases, other warning lights like the Traction Control System (TSC) may illuminate as well.

Most Likely Causes

1. Stuck Internal Oil Pressure Switch 🔴 High Probability → Shop Engine Oil Pressure Switch Mazda TSBs state this is caused by contamination in the transmission fluid causing the switch on the valve body to stick. This is a known weak point in the FW6A-EL transmission design.
   How to confirm: A technician will confirm this after ruling out software issues. The diagnosis is strongly suggested when P0847 appears with other codes like P0842, P0872, P0877, or P0780. The TSB repair procedure explicitly calls for replacing the switches if the TCM software is already up to date.
   Typical fix: Replace the internal oil pressure switches (Switch A and Switch B) located on the transmission's control valve body. This includes draining the fluid, removing the transmission pan, and carefully replacing the switches.
   Est. part cost: $100-$200 for the switches
2. Outdated Transmission Control Module (TCM) Software 🟡 Medium Probability → Shop Transmission Assembly Mazda released software updates to change the diagnostic logic and prevent this code from being triggered incorrectly by minor pressure fluctuations or contamination. The TSBs make this the first step in the diagnostic process for many vehicles within the affected range.
   How to confirm: A Mazda dealership or qualified shop with a Mazda-specific scan tool (like the Mazda IDS) can check the current software calibration file and see if an update is available based on the TSBs.
   Typical fix: Reprogram the TCM to the latest software version. This is often the first step in the official repair procedure. A Reddit user with a 2015 CX-5 reported that a TCM reprogram and transmission flush for $440 resolved their P0847 and P0780 codes.
   Est. part cost: $0 (labor cost only for reprogramming)
3. Low or Contaminated Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly While the primary cause is contamination causing a part to stick, extremely low or degraded fluid can also cause pressure-related faults. The Skyactiv transmission is sensitive to fluid type and condition.
   How to confirm: Check the transmission fluid level and condition. The fluid should be at the correct level and not appear dark, burnt, or contain excessive debris. A CX-5 owner on mazda6club.com recommended sending a fluid sample to a lab like Blackstone for analysis.
   Typical fix: Perform a transmission fluid drain and fill with the correct Mazda-specific ATF FZ. This is done as part of the pressure switch replacement anyway.
   Est. part cost: $80-$150 for fluid

Rare But Worth Checking

• Control Valve Body Failure: → Shop Transmission Valve Body If the passages within the valve body are blocked or damaged, or if solenoids have failed, replacing just the pressure switches may not solve the problem. In some cases, the entire valve body assembly needs to be replaced. This is a much more expensive repair.
• Wiring Harness Damage: While less common for this specific issue on this car, damage to the internal transmission wiring harness leading to the pressure switches can cause a fault. TSB 05-002/15 specifically warns to be careful not to damage the nearby ATF temperature sensor harness during switch replacement. A forum post mentioned a rash of CX-5s having this issue due to a wiring problem.

Diagnosis Steps

1. Use an OBD-II scanner to confirm P0847 and check for other related codes (P0842, P0872, P0877, P0780, P1738).
2. Consult a Mazda dealership or specialist to check the current TCM software version against the latest available calibration files mentioned in TSB #05-002-23 or earlier versions.
3. If the software is outdated, reprogram the TCM. This is the first step recommended by Mazda. Clear the codes and perform a test drive to see if the code returns.
4. If the code returns or the software is already current, the next step is to inspect the internal components.
5. Drain the transmission fluid and remove the transmission oil pan.
6. Visually inspect the fluid and pan for excessive metal shavings or debris, which could indicate a more severe internal problem. If significant debris is found, the oil strainer should also be replaced.
7. Locate and replace the oil pressure switches (A and B) on the control valve body as per the TSB instructions. 🎬 Watch: Step-by-step walkthrough of the internal pressure switch replacement. Be careful not to damage the nearby ATF temperature sensor harness during removal.
8. Reinstall the transmission pan with a new gasket, and refill with the correct specification of Mazda automatic transmission fluid (ATF FZ).
9. Perform the transmission's initial learning procedure with a compatible scan tool as specified in the workshop manual.
🎬 Watch: How to perform the SkyActiv transmission reset and learning procedure.
10. Clear all DTCs and perform an extended test drive to verify the repair.

Parts You'll Likely Need

• Transmission Oil Pressure Switch (OEM #FZ01-21-2C0) — This is the component that Mazda identifies as getting stuck and causing the code. They are typically replaced in pairs (A and B). The part number FZ01-21-2C0 is referenced in TSB 05-002/15.
  Trusted brands: Mazda OE
  OEM price range: $100-$200
  Aftermarket price range: $70-$150
• Automatic Transmission Fluid (ATF FZ) (OEM #0000-FZ-113E-01) — The transmission must be drained to access the internal switches. It must be refilled with this specific fluid. Use of non-specified fluid is not recommended.
  Trusted brands: Mazda OE, Idemitsu, Ravenol
  OEM price range: $20-$30 per quart
  Aftermarket price range: $15-$25 per quart
• Transmission Pan Gasket (OEM #FW6A-21-51X) — The pan gasket should be replaced whenever the transmission pan is removed to prevent leaks.
  Trusted brands: Mazda OE, Fel-Pro
  OEM price range: $30-$50
  Aftermarket price range: $20-$40
• Transmission Oil Strainer (Filter) (OEM #FZ01-21-500) — The TSB recommends replacing the strainer if a large amount of foreign material is found in the oil pan.
  Trusted brands: Mazda OE
  OEM price range: $40-$60
  Aftermarket price range: $25-$45

Related Codes That Often Appear With This One

• P0842 — Fault for Oil Pressure Switch No. 1. The TSBs list these codes together as part of the same known issue.
• P0872 — Fault for Oil Pressure Switch No. 3. Part of the same known issue.
• P0877 — Fault for Oil Pressure Switch No. 4. Part of the same known issue.
• P0780 — Indicates a 'Gear Shifting Malfunction,' a direct symptom of the pressure switch failure.
🎬 See: Understanding the P0780 shift malfunction code and its causes.
• P1738 — A Mazda-specific code for an 'Automatic transaxle internal malfunction,' often triggered alongside the pressure switch codes.

Technical Service Bulletins (TSBs) & Recalls

• 05-002-23: The most recent TSB, which supersedes older ones. It outlines the diagnostic flow: check for certain DTCs, then based on the model year, either reprogram the TCM first or proceed directly to replacing the pressure switches.
• 05-002/15: An earlier version of the TSB describing the same issue: 'Check Engine light and A/T Warning light on with one or more of these DTS (P0842, P0847, P0872, P0877, P0780) Stored in TCM Memory'. It details the part numbers for the switches and the procedure for replacement.

Platform-Specific Known Issues

• Mazda has issued multiple Technical Service Bulletins (TSBs) for this exact problem, including #05-002-23 and #05-002/15. These bulletins acknowledge the issue of sticking pressure switches due to fluid contamination and provide specific repair paths depending on the vehicle's VIN and current TCM software version.

Mechanic-Grade Diagnostic Values

• DTC Detection Temperature Threshold — expected: ATF temperature must be 20 °C {68 °F} or more for the TCM to log the fault.. Failure: N/A - This is a condition for diagnosis, not a failure value.
• Repair Verification Temperature — expected: ATF temperature should be warmed to 55 °C {131 °F} or more before performing the on-board diagnostic test to confirm the fix.. Failure: N/A - This is a condition for post-repair testing.
• Pressure Control Solenoid Resistance — expected: 5-7 ohms. Failure: A reading outside this range indicates a faulty solenoid on the valve body.
• On/Off Solenoid Resistance — expected: 11-14 ohms. Failure: A reading outside this range indicates a faulty solenoid on the valve body.

Hidden / Shadow Codes Worth Checking

• P1738:00: Automatic transaxle internal malfunction. While not a hidden code, the official Mazda diagnostic procedure for P0847 specifically checks if P1738 is also present. Its presence reinforces the diagnosis of an internal mechanical/hydraulic fault rather than a simple circuit issue. (see via Standard OBD-II scanner or Mazda IDS.)

Scan Tool Commands That Help

• Mazda IDS (Integrated Diagnostic Software): Module Reprogramming — This is the first step in the official TSB repair procedure for applicable VINs. It updates the TCM's diagnostic logic to be less sensitive to minor contamination, which can prevent the code from recurring.
• Mazda IDS (Integrated Diagnostic Software): Initial Learning Procedure — This must be performed after replacing the internal pressure switches and refilling the fluid. It allows the TCM to learn the characteristics of the new components and reset shift adapts.
• Mazda IDS or equivalent advanced scan tool: Live Data Monitoring — A technician can monitor the status PID for 'Oil pressure switch No. 2' to confirm if it is 'stuck on' during a test drive, which would directly validate the fault code's description.

Wiring & Ground Locations

• Internal Transmission Harness — Inside the transmission oil pan, connecting the valve body solenoids and switches to the main transaxle connector.. The pressure switches connect to this harness. TSBs specifically warn technicians to be careful not to damage the adjacent ATF temperature sensor harness when replacing the switches, indicating a delicate and tightly packed area prone to accidental damage during repair.

OEM Part Supersession History

• fza1212c0 → FZ01-21-2C0 — Part number update or revision.
  Heads up: FZ01-21-2C0 is the correct and current part number to order for the pressure switch referenced in the TSBs.

Model Year Variations Within This Range

• 2014-2016: The primary variation is the required fix based on the vehicle's VIN. Mazda TSBs specify certain VIN ranges that only require a TCM software update ('Module Reprogramming'), while other VINs outside that range require immediate replacement of the internal oil pressure switches. A dealer or specialist must check the VIN against the TSB to determine the correct initial procedure.