P0877 on 2014-2021 Mazda CX-5: Transmission Pressure Switch Fault Causes and Fixes

What's Unique About the 2014-2021 Mazda CX-5

For this specific generation of Mazda CX-5 with the SKYACTIV-Drive 6-speed automatic transmission (FW6A-EL) 🎬 Watch: A detailed overview of the Skyactiv Drive transmission internals., the P0877 code is rarely a simple sensor failure. Mazda has issued multiple Technical Service Bulletins (TSBs) acknowledging that the issue is "caused by the oil pressure switch A and/or B at the control valve body temporarily or permanently getting stuck due to contamination entering the passage." As a result, this code frequently appears with a cluster of other pressure switch and gear ratio codes, pointing directly to a failure within the transmission's control valve body assembly. This makes diagnosis more straightforward but often leads to a more complex repair than on other vehicles where a single sensor might be the culprit.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: The 2014-2021 year range covers both the first generation (KE, 2014-2016) and the second generation (KF, 2017-2021) of the Mazda CX-5. Both generations use a SKYACTIV-Drive 6-speed automatic transmission (FW6A-EL) and are covered by the relevant TSBs for this issue, indicating the problem can occur on either platform.

Symptoms You May Notice

• Check Engine Light is on
• Automatic Transaxle (A/T) warning light is on
• Harsh or erratic shifting
• Transmission slipping between gears
• Vehicle stuck in 'limp mode' (usually stuck in 3rd gear)
• Delayed engagement when shifting from Park or Neutral into Drive

Most Likely Causes

1. Internal Failure of the Control Valve Body 🔴 High Probability → Shop Transmission Valve Body Mazda TSBs #05-002-23, #05-004/18, and others state this is a known issue caused by contamination causing oil pressure switches (specifically Switch A and B) to stick inside the valve body assembly. Mazda implemented production changes to reduce contamination and improve diagnostic logic to address this.
   How to confirm: Scan the TCM for other related codes listed in the TSBs (P0842, P0847, P0872, P0780, P1738). If multiple codes are present, it strongly indicates a faulty valve body. A technician would then follow the TSB diagnostic tree, which may involve a TCM reflash before parts replacement depending on the VIN.
   Typical fix: Replace the entire control valve body assembly inside the transmission. In some cases, per the TSB for specific VIN ranges, a TCM software update is the first step and may resolve the issue without hardware replacement. If the valve body is replaced, an 'Initial Learning' procedure must be performed using a Mazda M-MDS scan tool. 🎬 Watch: How to reset the transmission for better shifting.
   Est. part cost: $800-$1500
2. Low or Contaminated Transmission Fluid 🟡 Medium Probability → Shop Transmission Assembly While internal contamination is the root cause described in the TSBs, using incorrect fluid can exacerbate issues. These transmissions require a specific low-viscosity blue fluid, Mazda ATF-FZ. Use of universal or other ATF types by non-specialist shops can lead to shifting problems and potential damage.
   How to confirm: Check the transmission fluid level and condition. The fluid should be at the correct level and blue in color (ATF-FZ). If it is red, brown, or smells burnt, the wrong fluid was used or there is severe internal wear.
   Typical fix: Perform a transmission fluid drain and fill using only Mazda ATF-FZ fluid. If the fluid is very dark or contains debris, the valve body is likely already compromised and will still need replacement.
   Est. part cost: $70-$150
3. Wiring or Connector Issue ⚪ Low Probability The transmission wiring harness is located underneath the vehicle and is exposed to the elements, which can lead to corrosion or damage over time. However, this is far less common than the internal valve body failure.
   How to confirm: Visually inspect the wiring harness and connectors going to the transmission for any signs of damage, corrosion, or loose connections. Test the circuit for proper voltage and ground according to the factory service manual.
   Typical fix: Repair the damaged section of wire or replace the corroded connector.
   Est. part cost: $20-$100

Rare But Worth Checking

• Faulty Transmission Control Module (TCM): → Shop Transmission Assembly A faulty TCM is rare. This should only be considered after all other possibilities, especially the valve body, have been ruled out. The TCM is integrated into the valve body on these models, so they are typically replaced as a single unit.

Diagnosis Steps

1. Scan for Codes: Use an OBD-II scanner to confirm P0877 and check for any other accompanying codes (P0842, P0847, P0872, P0780, P1738). The presence of these codes together is a strong indicator of the known TSB issue.
2. Check Transmission Fluid: Verify the transmission fluid level is correct and inspect its condition. The fluid should be clean and blue (Mazda ATF-FZ). Burnt-smelling or dark fluid indicates a more serious internal problem or use of incorrect fluid.
3. Inspect Wiring: Visually inspect the transmission's external wiring harness and main connector for any obvious signs of damage, corrosion, or loose pins.
4. Consult TSBs: Review Mazda TSBs #05-002-23, #05-004/18, or #05-002/15. These bulletins provide specific diagnostic flowcharts based on which codes are present and the vehicle's VIN.
5. Follow TSB Repair Path: The TSBs will guide a technician to either first attempt a TCM software update (for specific VIN ranges) or proceed directly to replacing the internal control valve body based on the vehicle's specific year and stored codes.
6. Professional Diagnosis: If you are not comfortable with these steps, take the vehicle to a qualified transmission shop or Mazda dealership. Inform them of the code and the relevant TSBs to avoid misdiagnosis.

Parts You'll Likely Need

• Transmission Control Valve Body Assembly (OEM #FZ21-21-100J (example, verify by VIN)) — This is the most common point of failure according to multiple Mazda TSBs. It contains the pressure switches that get stuck, causing the code. It is often replaced as a complete unit with the integrated TCM.
  Trusted brands: Mazda (OEM)
  OEM price range: $950-$1410
  Aftermarket price range: $240-$600 (Remanufactured)
• Mazda SKYACTIV-Drive ATF FZ Automatic Transmission Fluid (OEM #0000-FZ-113E-01) — The transmission fluid must be replaced when the valve body is serviced. Using the correct OEM fluid is critical for SKYACTIV transmissions.
  Trusted brands: Mazda (OEM)
  OEM price range: $20-$30 per quart
  Aftermarket price range: $15-$25 per quart

Related Codes That Often Appear With This One

• P0842 — Indicates Oil Pressure Switch No. 1 (Switch B) is stuck on; often triggered by the same valve body contamination issue.
• P0847 — Indicates Oil Pressure Switch No. 2 (Switch A) is stuck on; often triggered by the same valve body contamination issue.
• P0872 — Indicates Oil Pressure Switch No. 3 (Switch A) is stuck on; often triggered by the same valve body contamination issue.
• P0780 — Indicates a gear shifting malfunction, a direct symptom of the pressure control problem within the valve body.
• P1738 — A manufacturer-specific code for an automatic transaxle internal malfunction, confirming an internal problem as described in the TSBs.

Technical Service Bulletins (TSBs) & Recalls

• 05-002-23: The most recent TSB which groups P0877 with other DTCs indicating an internal transmission fault requiring diagnosis per the bulletin.
• 05-004/18: Supersedes older bulletins and covers 2013-2018 CX-5 models for the same set of transmission codes, pointing to contamination sticking the pressure switches and providing a diagnostic tree based on VIN.

Platform-Specific Known Issues

• Mazda has released a series of Technical Service Bulletins (e.g., #05-002-23, #05-004/18) for 2014-2021 CX-5 models (among others) that experience P0877 along with other codes. The bulletins state the cause is "contamination entering the passage" within the transmission, causing oil pressure switches on the control valve body to stick. The prescribed fix is often a replacement of the valve body and/or a TCM software update, depending on the vehicle's VIN and production date.

Mechanic-Grade Diagnostic Values

• Pressure Control Solenoid Resistance — expected: 5-7 ohms. Failure: A reading outside this range indicates a faulty solenoid.
• On/Off Solenoid Resistance — expected: 11-14 ohms. Failure: A reading outside this range indicates a faulty solenoid.
• Transmission Fluid Temperature for Initial Learning — expected: 40—110 °C {72—198 °F}. Failure: The 'Initial Learning' procedure will not start or will abort if the ATF temperature is outside this range.
• TFPS Sensor Reference Voltage — expected: ~5 volts. Failure: Incorrect or no voltage suggests a wiring or PCM/TCM issue rather than a sensor failure.

Scan Tool Commands That Help

• Mazda M-MDS (Mazda Modular Diagnostic System): Initial Learning [FW6A-EL, FWAX-EL] — This procedure is mandatory after replacing the control valve body or oil pressure switches. Failure to perform this can result in harsh shifting or engine rev-up, as the TCM needs to learn the characteristics of the new components.
• Mazda M-MDS: Module Reprogramming (TCM) — For specific VIN ranges outlined in TSBs like 05-004/18, reprogramming the TCM with the latest calibration is the first step to try and resolve the code before replacing any parts.

Wiring & Ground Locations

• Main Transmission Ground — A ground cable from the negative battery terminal bolts to a bracket on top of the transmission case.. This is the primary ground for the entire transmission assembly. A loose or corroded connection here can cause a wide range of electrical faults and erratic behavior from internal components like sensors and solenoids.
• G08 — Located at the right center of the dash.. This is a ground point for the Transmission Control Module (TCM). A poor connection at this specific point could cause low voltage reference signals and trigger codes like P0877.

Real Owner Repair Stories

• Mazdas247 Forum user (2013 Mazda CX-5) — Check Engine Light, Traction Control light, TPMS light, and Automatic Transaxle warning lights all came on. Vehicle would not exceed 20 mph.
  ❌ Tried (didn't work) Restarting the car did not clear the issue.
  ✅ What actually fixed it The dealership diagnosed a faulty valve body based on shift malfunction codes. The repair involved replacing the valve body (part # PEX2-21-C00), a clamp, and the transmission fluid, followed by a TCM 'relearn' procedure.
• Reddit user /u/ApartmentSlight2224 (2018 Mazda CX-5 with 80k miles) — Check engine light with code P0877.
  ❌ Tried (didn't work) A mechanic suggested the cheapest option would be to replace the entire transmission without performing further diagnostics.
  ✅ What actually fixed it A knowledgeable commenter advised against replacing the transmission, stating the proper, more cost-effective diagnostic path is to first test the specific solenoid ('B'), and if that fails, replace the valve body/TCM assembly. This follows the official Mazda TSB procedure and avoids an unnecessary, expensive full transmission replacement.

OEM Part Supersession History

• FZ21-21-100 (and others) → Various pre-programmed part numbers (e.g., PEY0-21-C00, PEX1-21-C00, etc.) — To simplify service procedures.
  Heads up: For vehicles produced on or before March 31, 2013, the original blank valve body was replaced by pre-programmed units. The new programmed valve bodies do not require a TCM configuration procedure upon installation, whereas the old blank ones did.
• PEX2-21-C00 → FZ21-21-100J (current example) — Standard part evolution and updates.
  Heads up: Part numbers must always be verified by VIN. The part number FZ21-21-100J is listed for 2015-2024 non-turbo models, indicating it supersedes earlier numbers like the one used in a 2013 repair.

Model Year Variations Within This Range

• 2014-2016 (example range): Per TSB 05-002/15, specific VIN ranges of early-generation CX-5s (and other models) are candidates for a TCM software update as the primary fix. If the vehicle falls outside this range, or if the software update does not work, the procedure defaults to parts replacement (valve body/switches).
• Pre- and post-April 2013 production: Vehicles produced on or before March 31, 2013, may have used a 'blank' valve body from the factory that required programming. Service replacements for these vehicles switched to 'pre-programmed' valve bodies, simplifying the repair process.