According to Au7o's analysis of 13,300+ owner reports, the 2004 Mazda MX-5 Miata has 4 documented known issues, with 1 rated critical. The most serious is Crankshaft Position Sensor Failure (NB) ($50-$250 repair). The most commonly reported issue is Soft Top Wear and Rear Window Delamination with 5,000 owner reports. Across all issues with published estimates, repair costs range from $50 to $1,500. DIY maintenance guides at au7o.io.
On the 1999-2005 Mazda MX-5 Miata 1.8L BP-Z3, the NB Miata (1999-2005) crankshaft position sensor (CPS) is a known failure point. The sensor deteriorates from engine heat, causing intermittent stalling, no-start conditions, and random misfires. Failure is often heat-related - the car runs fine when cold but stalls or dies after reaching operating temperature.
Engine stalls when hot, restarts after cooling down
Intermittent no-start condition (cranks but does not fire)
Random misfires and rough running at operating temperature
Check engine light with P0335 (CPS circuit) code
How to Fix
Replace crankshaft position sensor with OEM Mazda unit (N3A1-18-221A). Aftermarket sensors (Delphi, Dorman) have higher failure rates on this application. The sensor is located on the rear of the engine block near the flywheel.
Owner tips & cautions
TipCarry a spare CPS in the trunk - they fail without warning. Miata.net CPS mega-thread
TipRoute sensor wiring away from exhaust manifold heat to extend sensor life
High ConfidenceVerified4,500 reportsLast reported by owners Jul 2024Reviewed Feb 2026
Community reported
3,800 owners
On the 1990-2015 Mazda MX-5 Miata, all generations of Miata (NA through NC) are prone to rear main seal leaks as the engine ages. Oil seeps from the crankshaft rear seal, dripping onto the clutch housing and eventually contaminating the clutch disc. High mileage engines and infrequent oil changes accelerate seal deterioration. This is a labor-intensive repair as the transmission must be removed.
Oil dripping from bell housing area (bottom of engine/transmission junction)
Oil smell when parked
Clutch slipping if oil contaminates clutch disc
Low oil level between changes
How to Fix
Replace rear main crankshaft seal. Since the transmission must be removed, replace the clutch, throwout bearing, and pilot bearing at the same time if they are worn. Clean bell housing thoroughly to remove oil contamination.
Owner tips & cautions
TipReplace clutch, throwout bearing, and pilot bearing during rear main seal job - saves labor
TipUse Mazda OEM seal over aftermarket - better fitment and longevity. Miata.net seal replacement guide
TipA small amount of seepage is normal on high-mileage Miatas - only repair if dripping
High ConfidenceVerified3,800 reportsLast reported by owners Oct 2024Reviewed Feb 2026
Community reported
5,000 owners
On the 1990-2025 Mazda MX-5 Miata, miata soft tops deteriorate over time from UV exposure, flexing during operation, and age. Vinyl tops develop cracks and tears, cloth tops fade and shrink. The rear plastic window (NA/NB) or glass window (NC/ND) can delaminate from the top material, causing water leaks and reduced visibility. Expected soft top life is 7-10 years with proper care.
Common Symptoms
Visible cracks or tears in top material
Rear window yellowing, hazing, or separating from fabric
Water leaks into cabin during rain
Top material shrinking and pulling away from frame
Difficulty latching top due to shrinkage
How to Fix
Replace soft top assembly. OEM replacement is available but aftermarket options (Robbins, TwinTop) offer better materials at lower cost. For NA/NB, replace rear window at same time. Apply 303 Aerospace Protectant or RaggTopp UV treatment every 3-6 months to maximize top life.
Owner tips & cautions
TipNever fold the top with a cold/stiff rear window (NA/NB) - causes permanent creases and cracks
TipDIY soft top replacement is doable in a weekend with Miata.net installation guide
High ConfidenceVerified5,000 reportsLast reported by owners Nov 2024Reviewed Feb 2026
On the 1999-2005 Mazda MX-5 Miata, nB Miata radiators are prone to failure at the plastic upper tank where it crimps onto the aluminum core. The plastic becomes brittle with age and heat cycling, developing hairline cracks that leak coolant under pressure. This can lead to sudden coolant loss and overheating, especially in spirited driving or hot weather. The OEM radiator typically fails between 80,000-120,000 miles.
Common Symptoms
Coolant drip from front of radiator
Coolant overflow tank level dropping
Overheating in traffic or spirited driving
White residue on radiator top tank
Sweet coolant smell after driving
How to Fix
Replace the radiator with a full-aluminum aftermarket unit (Koyo, Mishimoto, CSF) for permanent reliability improvement, or use an OEM-style replacement. Replace the radiator cap and inspect all hoses. A thermostat replacement is recommended at the same time. Budget 1-2 hours for the swap. An aluminum radiator costs $150-$250 and eliminates the plastic tank failure point.
What are the most common Mazda MX-5 Miata problems?
According to Au7o's analysis of 13,300+ owner reports, the 2004 Mazda MX-5 Miata has 4 documented issues. The most frequently reported are: Crankshaft Position Sensor Failure (NB), Soft Top Wear and Rear Window Delamination, Rear Main Seal Oil Leak. Of these, 1 is rated critical and should be addressed promptly.
Is the Mazda MX-5 Miata reliable?
The 2004 Mazda MX-5 Miata has 4 known issues documented across 13,300+ owner reports. 1 issue is rated critical: Crankshaft Position Sensor Failure (NB). Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.
How much does it cost to fix common Mazda MX-5 Miata problems?
Repair costs for known Mazda MX-5 Miata issues range from $50 to $1,500, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, Crankshaft Position Sensor Failure (NB), typically costs $50-$250 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.
What is the 1999-2005 Mazda MX-5 Miata Crankshaft Position Sensor Failure (NB)?
The NB Miata (1999-2005) crankshaft position sensor (CPS) is a known failure point. The sensor deteriorates from engine heat, causing intermittent stalling, no-start conditions, and random misfires. Failure is often heat-related - the car runs fine when cold but stalls or dies af… Repairs typically run $50-$250. Severity: high.
What is the 1990-2025 Mazda MX-5 Miata Soft Top Wear and Rear Window Delamination?
Miata soft tops deteriorate over time from UV exposure, flexing during operation, and age. Vinyl tops develop cracks and tears, cloth tops fade and shrink. The rear plastic window (NA/NB) or glass window (NC/ND) can delaminate from the top material, causing water leaks and reduce… Repairs typically run $300-$1,500. Severity: medium.
What is the 1990-2015 Mazda MX-5 Miata Rear Main Seal Oil Leak?
All generations of Miata (NA through NC) are prone to rear main seal leaks as the engine ages. Oil seeps from the crankshaft rear seal, dripping onto the clutch housing and eventually contaminating the clutch disc. High mileage engines and infrequent oil changes accelerate seal d… Repairs typically run $400-$1,200. Severity: medium.
What is the 1999-2005 Mazda MX-5 Miata Radiator Coolant Overflow and Cracked Upper Tank (NB)?
NB Miata radiators are prone to failure at the plastic upper tank where it crimps onto the aluminum core. The plastic becomes brittle with age and heat cycling, developing hairline cracks that leak coolant under pressure. This can lead to sudden coolant loss and overheating, espe… Repairs typically run $200-$500. Severity: medium.
Content on this page was compiled with AI assistance using NHTSA complaints, TSBs, owner reports, and public automotive data. While we strive for accuracy, this information may contain errors. Always verify repair procedures and specifications with your vehicle's service manual or a qualified mechanic.
