On a Honda Odyssey, the P0420 Bank 1 code points to the catalytic converter on the Bank 1 side not meeting the required efficiency, and the relevant downstream oxygen sensor (O2S-2) for that bank is located after the catalytic converter on the same bank—typically on the driver’s side of the V6 engine.
Bank 1 is the side of the engine that contains cylinder 1. In most Odyssey models with a transverse-mounted 3.5L V6, Bank 1 is the left/driver’s side. P0420 is a catalyst-related diagnostic code, though a faulty sensor or exhaust leak can mimic it. Locating Bank 1’s downstream O2 sensor is usually the first step in diagnosing the issue.
Locating Bank 1 Sensor 2 on a Honda Odyssey
Use this guide to locate the downstream oxygen sensor for Bank 1. Exact placement can vary slightly by year and trim, but the general layout remains consistent.
- Park on a flat, level surface and ensure the engine is cool. Safely raise and support the vehicle if needed to access the undercarriage.
- Trace the exhaust path from the front of the engine toward the rear. Identify the catalytic converter on the Bank 1 side (the bank containing cylinder 1).
- Look for the downstream O2 sensor (O2S-2) installed after the catalytic converter on that bank; its wiring harness runs toward the engine bay and is usually secured to the exhaust pipe.
- Confirm the connector type and color match the downstream sensor on Bank 1; it will typically be a multi-pin connector feeding the sensor’s signal to the ECU.
Concluding: Locating Bank 1 Sensor 2 is the first practical step in diagnosing a P0420; once found, you can test or inspect the sensor and associated wiring for faults before moving to catalytic converter diagnostics.
Understanding and Diagnosing P0420 Bank 1
P0420 indicates the catalytic converter on Bank 1 is not achieving the expected efficiency according to the downstream O2 sensor readings. For the Honda Odyssey, Bank 1 is the side that includes cylinder 1; the V6 engine in most Odysseys uses a shared exhaust with two banks, making Bank 2 the opposite side. While a failing catalytic converter is a common cause, issues with the Bank 1 downstream sensor, exhaust leaks, or fuel management can trigger or mimic the code.
To diagnose effectively, perform these basic checks:
- Inspect for exhaust leaks around the Bank 1 downstream area and around the catalytic converter and sensor connections.
- Test or replace Bank 1 Sensor 2 if it shows sluggish response, dirt, or wiring damage; ensure the connector is clean and secure.
- Compare Bank 1 vs Bank 2 downstream O2 sensor readings with a scan tool to determine if Bank 1 is consistently underperforming.
- Assess fuel trims, misfires, and overall engine performance, since persistent misfires or poor combustion can affect catalytic converter efficiency.
Concluding: If the code persists after basic checks, more thorough testing of the catalytic converter’s condition may be required, which could involve professional diagnostics and potential replacement of the converter or related exhaust components.
Summary
The P0420 Bank 1 code on a Honda Odyssey signals a possible issue with the catalytic converter efficiency on the Bank 1 side. The key to diagnosing this code is locating Bank 1 Sensor 2, the downstream O2 sensor after the Bank 1 catalytic converter, which is typically on the driver’s side of the V6 engine. Follow systematic checks—sensor function, wiring, leaks, and fuel management—to determine whether the problem lies with the converter, the sensor, or other exhaust/system issues.
How much does it cost to repair a P0420 Bank 1?
Most Common Causes of P0420 Code
| Cause | Typical Repair Cost (USD) |
|---|---|
| Failing catalytic converter | $500-$2,500 |
| Faulty oxygen sensor (upstream or downstream) | $150-$400 |
| Exhaust leaks (manifold, pipes) | $100-$600 |
| Engine misfire (spark plugs, coils) | $100-$500 |
Where is the bank 1 catalytic converter on a Honda Odyssey?
Located close to firewall side of engine, BANK 1.
Is P0420 a serious problem for my Honda?
How Serious Is the P0420 Code? Driving your car with the P0420 code will only lead to further damage to the catalytic converter. Plus, the problem can affect other parts of the car, such as the fuel line and exhaust systems.
Is the code P0420 Bank 1 or 2?
A vehicle's Powertrain Control Module (PCM) triggers Diagnostic Trouble Code (DTC) P0420: “Catalyst System Efficiency Below Threshold (Bank 1)” when the pre- and post-catalytic converter oxygen sensor readings do not fall within expected parameters.