What P0135 Means for Your 2020 Honda Ridgeline
The P0135 code on your 2020 Honda Ridgeline signals a malfunction in the oxygen sensor heater circuit for Bank 1, Sensor 1. Your Ridgeline runs Honda's J35Y6 3.5-liter V6 engine, and Bank 1 is the side of the engine closer to the firewall. The upstream O2 sensor on that bank monitors exhaust gases before they enter the catalytic converter, and it depends on an internal heater element to reach its 600°F operating temperature quickly after a cold start.
Why the Heater Exists
Without the heater, your Ridgeline's O2 sensor would take several minutes to warm up using exhaust heat alone. During that time, the ECM runs in open-loop mode, using pre-programmed fuel maps rather than real-time feedback from the sensor. This means richer fuel mixtures and higher emissions. The heater circuit gets the sensor operational within 20 to 30 seconds, allowing the engine to switch to closed-loop operation quickly.
Common Causes on the Ridgeline V6
- Burned-out O2 sensor heater element (High Likelihood): The Ridgeline uses Denso OEM sensors. The internal heater coil can fail from thermal fatigue, especially on trucks that tow regularly since the exhaust runs hotter under load. The V6 configuration means the sensor on Bank 1 is tucked behind the engine, where heat exposure is more intense.
- Corroded wiring or connector (Medium Likelihood): The Ridgeline's unibody truck design places the O2 sensor wiring in a path that is exposed to road spray. Salt, mud, and moisture can corrode the connector pins or damage insulation on the wiring harness.
- Blown heater circuit fuse (Medium Likelihood): Check the underhood fuse box for the O2 heater relay fuse. On the Ridgeline, this is typically a 15A or 20A fuse. A simple blown fuse is the cheapest fix possible.
- ECM ground or relay failure (Low Likelihood): The ECM controls the ground side of the heater circuit. A failed driver within the ECM or a bad relay can prevent the heater from receiving power. This is rare and usually accompanied by other diagnostic codes.
Diagnostic Steps
Step 1: Check the Fuse First
Open the underhood fuse box on your Ridgeline and locate the O2 sensor heater fuse. Pull it and check for a broken element or test continuity with a multimeter. If blown, replace it and clear the code. If it blows again immediately, you have a short circuit downstream.
Step 2: Access and Inspect the Sensor
On the 3.5L V6, the Bank 1 upstream sensor sits on the rear exhaust manifold near the firewall. Access is tight on the Ridgeline compared to conventional truck frames. You may need to work from underneath the vehicle. Inspect the sensor connector for corrosion, melted wires, or damage from heat exposure.
Step 3: Measure Heater Resistance
Unplug the sensor and test heater resistance across the heater pins. A good Denso sensor reads 2 to 14 ohms. An open reading means the heater element is burned out and the sensor needs replacement. Also check for battery voltage at the harness-side connector with the key on to confirm power is reaching the sensor.
Step 4: Check for Additional Codes
If you also see codes like P0155 (Bank 2 Sensor 1 heater) or other heater-related codes, the problem is more likely a shared fuse, relay, or ECM issue rather than an individual sensor failure.
Repair Costs
An OEM Denso upstream O2 sensor for the 2020 Ridgeline V6 runs $100 to $180. Aftermarket options are available from $40 to $80 but are less reliable on Honda's ECM systems. Shop labor for the Bank 1 sensor runs $120 to $200 because of the tight access behind the V6. DIY is possible but more challenging than on an inline-four due to the sensor location. Budget a total of $200 to $380 at a shop.
Ignoring the Code
A P0135 will not stop your Ridgeline from running, but you will burn more fuel during cold starts and you will fail emissions testing. Extended rich running during warm-up can prematurely age your catalytic converter, which costs $800 to $2,000 to replace on the V6 Ridgeline. Fix this code sooner rather than later.