P0135 on the 2018 Honda Civic
The 2018 Honda Civic (10th generation) uses either a 2.0L naturally aspirated R20A (158 hp) or a 1.5L turbocharged L15B7 (174-205 hp depending on trim and Si variant). The P0135 code indicates the upstream O2 sensor heater circuit has malfunctioned. By 2018, many of these Civics have accumulated enough mileage and thermal cycles that heater element burnout is a common and expected maintenance item.
Why the 2018 Civic Is Prone to P0135
With the 2018 Civic now having 6-8 years of service and potentially 60,000-120,000 miles, the O2 sensor heater element has endured tens of thousands of heating and cooling cycles. Each cold start activates the heater, and over time the internal resistance wire fatigues and breaks. This is a normal wear item, not a defect. The 1.5T model may see slightly earlier heater failure due to higher overall exhaust temperatures from the turbocharger.
Causes Ranked by Likelihood
- Burned-out heater element: By far the most common cause on a 2018 Civic. The internal resistance wire has simply reached the end of its service life. This is a replace-the-sensor fix.
- Blown heater fuse: The underhood fuse box contains a dedicated heater fuse. Check this first, as it is a sub-$10 fix. If the fuse keeps blowing, there is a short circuit somewhere.
- Corroded connector: After years of exposure to road salt, water, and heat, the O2 sensor connector can develop corrosion that increases resistance in the heater circuit. Common on Civics in northern states.
- Wiring degradation: The heater circuit wiring near the exhaust manifold can develop brittle insulation from heat exposure, eventually causing shorts or opens in the circuit.
Impact on Your Civic
The check engine light will be on. Cold starts may feel slightly rougher, and fuel economy on short trips decreases as the engine stays in open-loop mode longer. However, once the sensor warms from exhaust heat (2-5 minutes), normal closed-loop operation resumes. You will fail an emissions test with this code active.
Diagnosis
- Check the O2 sensor heater fuse in the underhood fuse box first.
- Disconnect the sensor and measure heater resistance. Expect 2-15 ohms. Open circuit = burned heater.
- Check for 12V power at the heater connector pins with key on.
- Inspect the connector for green corrosion or water damage.
- Check the wiring for heat damage near the exhaust manifold.
Repair Costs
The 2018 Civic is affordable to repair. OEM Denso sensor: $75-$155. Quality aftermarket (Bosch, NGK, Denso non-OE): $35-$75. Dealer labor: $100-$170. Total dealer repair: $175-$325. Independent shop: $120-$230. Fuse: $5-$10. The 2018 Civic is likely outside the basic warranty but may still be within the federal emissions warranty (8 years/80,000 miles) depending on your purchase date and mileage.
DIY
The upstream O2 sensor on the 2018 Civic is very accessible. On both the 2.0L and 1.5T, the sensor can be reached from above. Use a 22mm O2 sensor socket. Since these sensors have been heat-cycled for years, they may be seized in the bung. Apply penetrating oil the night before and give it time to work. Use a breaker bar for initial breakaway torque. This is a straightforward 30-45 minute DIY job.