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P1135, P0455, and P0140 OBD2 Error Diagnosis for 2000 Mazda Miata - Common Causes and Fixes

Model: 2000 Mazda Miata Fault Code: P0140 Posted: 2007-04-18 00:14

I own a 2000 Mazda Miata with regular maintenance, but I'm currently experiencing three OBD-II diagnostic errors: P1135 (O2 Sensor A2 Signal Stuck High), P0455 (EVAP System Leak Detected), and P0140 (O2 Sensor B1 Signal Malfunction). The check engine light has been on for several weeks. I recently had the timing belt replaced, so I'm wondering if these codes are related to loose electrical connections or wiring issues. While it's unusual to have both oxygen sensors failing simultaneously along with a significant EVAP leak, I've already replaced both O2 sensors within the past 18 months (30k miles). I'm seeking input from other owners of 2000 Mazda Miata models who have encountered similar issues. Has anyone successfully diagnosed and resolved these codes? What steps did you take—such as inspecting wiring harnesses, replacing ignition components, or addressing fuel system leaks? Any advice on troubleshooting order (e.g., starting with basic components before moving to expensive repairs) would be greatly appreciated.

Related fault codes

P0140P0455P1135

Comments (6)

Anonymous 2007-04-18 15:52

If you recently had the timing belt replaced, it's worth checking whether any related wiring or connectors were disturbed during installation. The shop that performed the work should review their procedures and inspect for loose or damaged connections—especially in the sensor harnesses or ECU-related circuits. A simple visual inspection of all O2 sensor connectors could resolve P1135 and P0140 issues.

Anonymous 2007-06-03 14:53

My '99 Mazda Miata has 42,000 miles. Three years ago, we replaced ignition wires and the ignition module ($300+), which was under warranty. After filing a complaint with Mazda's Japanese headquarters, the dealer replaced the catalytic converter at no cost—originally priced around $1,000. The issue resolved itself until about six months ago. Since then, I’ve ignored it and recently replaced the ignition cables myself using an OBD-II reader (a tool I’d never used before on my 1996 Toyota with 167,000 miles). As of today, the check engine light is off. This suggests that ignition-related components may play a role in sensor signal integrity. Before investing heavily, try basic repairs first—like replacing ignition cables or inspecting wiring harnesses. While Mazda Miata is a fun and reliable car, I’m now 50 and won’t buy another one from the brand due to recurring reliability issues. Zoom zoom—this car brings joy, but not at the cost of long-term durability. LuF

Anonymous 2007-06-03 14:57

I understand your frustration—but Mazda vehicles are generally well-engineered. These issues might stem from component aging or environmental exposure rather than poor design. A deeper understanding of vehicle systems, such as fuel trim and sensor calibration, may help in diagnosing the root cause over time.

Anonymous 2007-06-04 06:54

We had a humid morning recently—the check engine light came back on. I’m considering selling the car by summer’s end. Mazda isn’t inherently bad—it just doesn’t meet expectations when compared to other brands, especially in reliability under real-world conditions. My friends who own Korean-made vehicles (all of which are excellent) have noted similar trends, suggesting a broader industry gap. I hope others find better solutions. Best of luck with your Miata journey. LF

Anonymous 2007-06-04 07:53

It’s possible that no car is perfect—every model has latent issues under certain conditions. The key is identifying which components are most vulnerable and addressing them proactively.

Anonymous 2007-06-04 11:11

Yes, even well-engineered vehicles can develop hidden problems over time. Regular maintenance and early detection of sensor or wiring faults are critical to preventing costly repairs later on.