P0204 on 2014-2016 Mazda 6 SKYACTIV-G 2.5L: Injector Circuit Fault Causes and Fixes

What's Unique About the 2014-2016 Mazda 6

For this generation of Mazda 6, P0204 has a very specific and documented history. Mazda issued Technical Service Bulletin #01-017/16 (later superseded by #01-004/17) for a known issue where an internal failure in certain DENSO-made PCMs would cause injector circuit codes to appear in pairs (P0201 with P0204). This means that unlike many other vehicles where P0204 points directly to the cylinder 4 injector or its wiring, on this Mazda 6 it could be a symptom of a faulty engine computer. This issue also affects the 2014-2016 Mazda 3 and 2013-2016 Mazda CX-5 from the same era that share the same engine and PCM.

Symptoms You May Notice

• Check Engine Light is on
• Rough or shaking engine idle
• Engine misfire, which may also trigger a P0304 code
• Hesitation or stumbling during acceleration
• Reduced engine power
• Poor fuel economy
• Vehicle may stall or be difficult to keep running

Most Likely Causes

1. Faulty Powertrain Control Module (PCM) 🔴 High Probability → Shop Engine Control Module (ECM) A known issue documented in Mazda TSBs #01-017/16 and #01-004-17 affects certain DENSO-made PCMs in Japan-built vehicles with VINs lower than JM1GJ**484154 (produced before May 23, 2016), causing an internal failure that specifically triggers paired injector codes like P0201 and P0204.
   How to confirm: Scan for other diagnostic trouble codes. If P0201 is present along with P0204, the PCM is the most likely cause. A technician can also inspect the PCM label to confirm it is a DENSO unit as described in the TSB.
   Typical fix: Replace and reprogram the Powertrain Control Module. This must be done by a dealer or a qualified shop with access to Mazda's M-MDS software.
   Est. part cost: $800-$1200
2. Faulty Cylinder 4 Fuel Injector 🟡 Medium Probability → Shop Fuel Injector Direct injection injectors operate under high pressure and can fail electrically over time.
   How to confirm: If P0204 appears alone, the injector is a more likely suspect. Swap the cylinder 4 fuel injector with another cylinder (e.g., cylinder 3). Clear the codes and run the engine. If the code changes to P0203, the injector is confirmed to be faulty. Alternatively, check the injector's resistance with a multimeter. While official specs are around 1.74–2.04 ohms, forum users report a normal reading is closer to 12-13 ohms; a failed injector will show an open circuit (infinite resistance) or a reading far from a known-good injector. 🎬 Watch: How to test a faulty Skyactiv fuel injector
   Typical fix: Replace the faulty fuel injector. It is often recommended to replace the full set on high-mileage vehicles. 🎬 See this guide on Skyactiv injector removal tips
   Est. part cost: $50-$150
3. Wiring Harness or Connector Issue ⚪ Low Probability Engine vibration and heat can cause wires to fatigue, break, or chafe over time, especially near the injector connector.
   How to confirm: Visually inspect the wiring harness and connector for the cylinder 4 fuel injector for any signs of damage, corrosion, or loose pins. Use a multimeter to perform a continuity test on the circuit between the injector connector and the PCM connector.
   Typical fix: Repair or replace the damaged section of the wiring harness or the connector.
   Est. part cost: $10-$100

Diagnosis Steps

1. Scan for Diagnostic Trouble Codes (DTCs). Check if P0204 is present alone or with P0201. The presence of P0201 strongly suggests a PCM failure per Mazda TSB #01-017/16.
2. If P0201 and P0204 are present, check the vehicle's VIN. If it is lower than JM1GJ**484154 (for Mazda 6), the TSB applies and the PCM is the highly probable cause.
3. If P0204 is the only code, perform a visual inspection of the cylinder 4 fuel injector wiring and connector for any obvious damage, corrosion, or loose connections.
4. Use a noid light to test the injector signal. Disconnect the injector and plug in the noid light. Start the engine; the light should flash, indicating the PCM is sending a pulse. If it doesn't flash, or stays on continuously, the problem is in the wiring or the PCM driver.
🎬 Watch: How to test the injector circuit with a test light
5. If the noid light flashes, the injector is the next suspect. Turn the engine off and measure the internal resistance of the injector with a multimeter. Compare the reading to another cylinder's injector. A reading of infinite resistance (Open Loop) or a value significantly different from the others indicates a faulty injector.
6. As a final confirmation, swap the cylinder 4 injector with an adjacent one (e.g., cylinder 3). Clear the codes and drive the vehicle. If the code returns as P0203, the fuel injector is faulty and needs to be replaced.
7. If the code P0204 returns after the swap, the issue lies in the wiring harness. Perform a continuity test with a multimeter on the power and signal wires between the injector connector and the PCM connector to find the open or short circuit.

Parts You'll Likely Need

• Powertrain Control Module (PCM) (OEM #PY8D-18-881, PY1R-18-881E, PYXW-18-881A (Varies by VIN, must be verified)) — This is the most likely cause if P0204 appears with P0201, due to a known internal failure documented in Mazda TSB #01-017/16.
  Trusted brands: Mazda (OEM)
  OEM price range: $800-$1200
  Aftermarket price range: $250-$600 (Remanufactured, requires cloning)
• Fuel Injector (OEM #PY01-13-250) — This is the most likely part to fail if P0204 appears by itself, without P0201.
  Trusted brands: Bosch, Denso, Mazda (OEM)
  OEM price range: $120-$200
  Aftermarket price range: $50-$150

Related Codes That Often Appear With This One

• P0201 — According to Mazda TSBs, an internal PCM failure often causes injector circuit codes for cylinders 1 and 4 to appear together. This is the strongest indicator that the PCM is the root cause.
• P0304 — This code means 'Cylinder 4 Misfire Detected.' Since P0204 indicates a problem with fuel delivery to cylinder 4, a misfire is an expected and direct consequence. The TSB confirms misfire codes are usually stored at the same time.
• P0300 — This code indicates a random or multiple cylinder misfire. It can be triggered if the primary fault in the cylinder 4 injector circuit is severe enough to disrupt the engine's overall balance and timing, especially if paired with a P0201 fault.

Technical Service Bulletins (TSBs) & Recalls

• 01-017/16: Specifies affected models (Mazda3, Mazda6, CX-5) and VIN ranges for a known PCM failure causing paired injector codes. Confirms the issue is with DENSO-produced PCMs before May 23, 2016.
• 01-004-17: Supersedes the earlier bulletin, noting that a rough running engine with DTCs P0201/P0204 or P0202/P0203 may be caused by an internal PCM failure.

Platform-Specific Known Issues

• A Technical Service Bulletin (TSB #01-017/16, superseded by #01-004-17) was issued for 2014-2016 Mazda 6 models (among others) built in Japan with VINs lower than JM1GJ**484154. It applies to vehicles with DENSO PCMs manufactured before May 23, 2016. It details an internal PCM failure that causes DTCs P0201 and P0204 (or P0202 and P0203) to be stored simultaneously.

Mechanic-Grade Diagnostic Values

• Fuel Injector Internal Resistance — expected: 1.74–2.04 ohms at 20°C (68°F). Some sources cite a slightly wider range of 1.6-2.52 ohms.. Failure: A reading of 0 ohms (short circuit) or OL/infinite resistance (open circuit). The key is to compare the reading from cylinder 4 to a known-good cylinder.
• Injector Circuit Voltage (Key On, Engine Off) — expected: ~12V (Battery Voltage) on the power feed wire at the injector connector.. Failure: Low or no voltage suggests a problem with the power supply, such as the INJECTOR 30A fuse or the fuel injector relay.
• Injector Pulse Width (Live Scan Tool Data at Idle) — expected: 1-5 milliseconds (ms), varying with engine load.. Failure: A value of 0 ms for cylinder 4 while other cylinders show normal readings points to a circuit or PCM driver failure.
• High Pressure Fuel Pump Pressure (at full throttle) — expected: At least 2,176 psi.. Failure: While not a direct test for P0204, low high-side pressure could indicate broader fuel system issues.
• PCM Fault Trigger Condition — expected: The PCM must not receive the fuel injection verification signal for 25 consecutive times.. Failure: When this condition is met, the PCM determines an open circuit exists and stores DTC P0204.

Hidden / Shadow Codes Worth Checking

• P0204:00: This is the full code format often displayed on more advanced scanners like the Mazda M-MDS. The ':00' suffix is a component identifier that doesn't typically change the diagnosis but confirms the code relates to the general circuit fault. The TSBs for the PCM issue reference this full code format. (see via Mazda M-MDS, FORScan, or other professional-grade scan tools.)

Scan Tool Commands That Help

• FORScan: Injector 'Buzz Test' — FORScan, a powerful software tool for Ford and Mazda vehicles, can perform an 'injector buzz test'. This command individually actuates each injector, allowing a technician to listen for an audible click or 'buzz'. If cylinder 4's injector is silent while others buzz, it points to a failure in the injector itself or its immediate wiring/driver. This is a quick, non-invasive way to help isolate the fault.
• Mazda M-MDS (Mazda Modular Diagnostic System): PCM Replacement & Programming — If the PCM is diagnosed as faulty per the TSB, a new PCM must be installed and programmed using the dealer-level M-MDS. This process pairs the new computer to the vehicle's immobilizer system and ensures it has the latest corrected software. Aftermarket shops may use J2534 pass-through devices with a Mazda software subscription.

Wiring & Ground Locations

• PCM Pin 1DS — At the Powertrain Control Module (PCM) main harness connector.. This is the specific pin for the control circuit from the PCM to the #4 fuel injector (at terminal A of the injector connector). An open circuit or short between this pin and the injector is a direct cause of P0204.
• PCM Pin 1DT — At the Powertrain Control Module (PCM) main harness connector.. This is the specific pin for the power circuit from the PCM to the #4 fuel injector (at terminal B of the injector connector). A fault on this wire can also trigger the code.
• Main Engine Grounds — Key grounding points include the body on the passenger side near the power steering reservoir, a ground on top of the transmission, two on the front of the transmission, one at the passenger motor mount, and the main ground from the driver's side fender area to the negative battery terminal.. While not a primary cause for a single injector code, a poor or corroded engine ground can cause a host of bizarre electrical issues, including intermittent injector circuit problems. Verifying these grounds are clean and tight is a crucial step in any electrical diagnosis.

Real Owner Repair Stories

• YouTube Repair Channel (Vehicle with P0204 (Not specified as Mazda, but demonstrates a universal cause)) — Check Engine Light with code P0204.
  ❌ Tried (didn't work) The owner assumed the injector was bad.
  ✅ What actually fixed it The wiring harness connector at the fuel injector was not fully seated and had come loose. The retaining clip was missing or broken. Pushing the connector back on until it clicked and securing it resolved the P0204 code instantly.
• Mazdaspeeds.org Forum User (2013 Mazdaspeed3 (different model, but direct injection engine with similar failure mode)) — P0204 and P0304 codes appearing only on cold starts. The engine would misfire, but run fine after a restart.
  ❌ Tried (didn't work) The user had recently cleaned valves and injectors professionally. The problem appeared 3 months later.
  ✅ What actually fixed it The user suspected the injector was failing intermittently. Although the final fix was not posted in the thread, the detailed description of a cold-start-only electrical fault strongly points to an injector coil that is failing when cold (contracted) and making a connection once warmed up (expanded), or a hairline crack in the wiring that behaves similarly with temperature changes.

OEM Part Supersession History

• Various DENSO PCMs prior to May 2016 → Updated Mazda OEM PCM (part number varies by VIN) — The original DENSO-produced PCMs had an internal manufacturing defect that led to the failure of injector driver circuits, specifically causing paired codes like P0201/P0204. The replacement parts have eliminated this internal failure.
• PY01-13-250 → No official supersession noted, this part number remains current.
  Heads up: This part number (PY01-13-250) is used across a wide range of Mazda vehicles with the 2.5L engine, including the Mazda3, Mazda6, CX-5, CX-9, and CX-30. Fitment is consistent for the specified model years.

Model Year Variations Within This Range

• 2014-2016 (Japan-built before May 23, 2016): Vehicles built before May 23, 2016, with VINs lower than JM1GJ**484154 are susceptible to the PCM failure described in TSB #01-017/16. Vehicles built after this date have the corrected PCM and are not prone to this specific paired-code failure.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Infotainment 'Ghost Touch' and Screen Failure 🟠 Medium — Very common on 2014-2016 models. The touchscreen may register phantom inputs or become unresponsive, often due to heat/UV damage. (Ref: Multiple TSBs exist (e.g., 09-021/22, 09-003/22) and a Customer Service Program (CSP13) extends the warranty for the Connectivity Master Unit (CMU), but not always the screen itself.)
• Premature Rear Brake Wear / Seizing Calipers 🟠 Medium — Commonly reported issue where rear brake pads wear out faster than fronts, sometimes due to sticking parking brake mechanism or seized caliper slide pins. (Ref: Recall 1217F (NHTSA Campaign 17V384000) was issued for 2014-2015 models for a parking brake actuator shaft that could corrode and bind.)
• Faulty Ignition Coils 🟡 Low — TSB #01-014-16-3208A identified 'YUMEBISHI'-brand ignition coils on 2014-2016 models as prone to failure, causing misfires (P0300-P0304). (Ref: TSB #01-014-16-3208A)
• Shifter Park Switch Failure 🟡 Low — On early models, a switch in the shifter assembly can fail, preventing the car from shutting off completely and draining the battery.
• Transmission Whining Noise (Early 2014 models) 🔴 High — A defective bearing in the transaxle case caused a whining noise that increased with speed on some early 2014-2015 models, often requiring transmission replacement under warranty. (Ref: A TSB was issued in 2015 for affected vehicles under warranty.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used fuel injector from a reputable salvage yard with a known low-mileage donor vehicle can be a cost-effective option, especially if P0204 appears alone. A used PCM is NOT recommended unless you are using a specialized cloning service.

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 fuel injector, inspect the connector for corrosion and the tip for physical damage. Ask for the donor vehicle's mileage.
• For a PCM, ensure the part number is an exact match. Inspect for any signs of water damage, corrosion on the pins, or physical case damage. Verify if it's from a vehicle manufactured after May 2016 to get the revised part.

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

• Powertrain Control Module (PCM): Due to the known TSB, a new OEM Mazda PCM is the guaranteed fix. While remanufactured units exist, they may not have the updated internal components that prevent a repeat failure. Any replacement PCM, new or used, requires dealer-level programming or cloning.

Aftermarket brands forum-validated for this vehicle:

• Bosch
• Denso (OEM supplier)

Brands owners have reported issues with on this vehicle:

• Unnamed, no-brand 'white box' injectors from online marketplaces. These often have inconsistent spray patterns and flow rates, which can cause performance issues even if they resolve the electrical code. One seller notes that aftermarket parts should not be mixed with genuine ones due to potential differences in oil output and atomization.

Real Owner Stories

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

Related OBD-II Codes

• P0201 — Often appears simultaneously with P0204 on 2014-2016 Mazda 6 models due to a specific internal PCM failure documented in TSB #01-017/16.
• P0202 — Another injector circuit code that may pair with P0203 due to the same internal PCM driver failures mentioned in TSB #01-004-17.
• P0203 — The code that will appear if a faulty cylinder 4 injector is moved to cylinder 3 during diagnostic swapping.
• P0304 — A cylinder 4 misfire code that is frequently triggered as a result of the injector circuit failure (P0204).
• P0300 — A random/multiple cylinder misfire code that can be triggered by faulty 'YUMEBISHI' brand ignition coils or injector circuit issues.

Frequently Asked Questions