P0430 Code: Catalyst System Efficiency Below Threshold (Bank 2)

What happens if you don't fix it

Symptoms you can actually notice

• Check engine light steady
• Failed emissions test
• Slight power loss

What the computer is actually complaining about

The rear oxygen sensor on bank 2 watches what leaves the converter on that side. The computer compares its slow signal against the fast-switching sensor ahead of the converter. When the two read alike, the converter has stopped storing oxygen. That comparison runs over two drive cycles before the light comes on.

Most likely causes, cheapest check first

What you need in your hands

• OBD-II scanner with live data

  Any $25 Bluetooth reader plus a free phone app shows both rear sensor voltages. Shop-grade tools add nothing here.

• Infrared thermometer Optional

  $20 at a hardware store. Reads converter inlet and outlet temperature without touching hot metal.

• Exhaust smoke machine Optional

  A shop charges $80 to $150 for a smoke test. Rent one for $60 if a leak is suspected.

Test it yourself, step by step

Do these in order. Each step tells you what to do, what to look at, what counts as fine, what counts as broken, and what you will actually see.

1. 1 Plug the scanner into the trapezoid port under the dash on the driver side, above your left knee. Warm the engine, then open live data and watch both oxygen sensor voltages on bank 2.

   Look at

   How fast each trace moves on the screen. The front sensor should switch constantly and the rear one should hold almost still.

   Fine if

   The front sensor swings between 0.1V and 0.9V several times per second while the rear sensor sits near 0.6V to 0.8V.

   Broken if

   The rear sensor switches as fast as the front one, or the front sensor sits flat near 0.45V. A dead front sensor fakes a dead converter.

   What you'll see Two traces. The top one jumps up and down. The bottom one is a nearly straight line with small drift.

2. 2 Open the hood and follow the exhaust pipe down the passenger side of the engine bay. Bank 2 sits on the side away from cylinder 1, so on a transverse V6 it faces the radiator.

   Look at

   Listen along the pipe and flanges for a tick or hiss that speeds up with the engine. Look for black soot at the joints.

   Fine if

   A soft even note with no soot at any flange between the manifold and the converter.

   Broken if

   A tick that follows engine speed, or a soot streak at a joint. Air entering ahead of the converter sets this code on its own.

   What you'll see Your hand near the pipe feels steady pulses. A sharp tick means a leak, and a leak costs far less to fix than a converter.

3. 3 Point an infrared thermometer at the pipe before the converter, then behind it, holding it two inches away each time with the engine fully warm.

   Look at

   The temperature gap between the inlet pipe and the outlet pipe, measured a few seconds apart at the same distance.

   Fine if

   The outlet reads 30F to 100F hotter than the inlet, which means the converter is still burning leftover fuel.

   Broken if

   The two readings sit within 20F of each other, or the outlet is cooler. That points at the converter itself.

   What you'll see Two numbers on the display. Write both down before you talk to any shop about a converter.

4. 4 Switch the scanner to fuel trims and misfire counters. Let the engine idle for two minutes, then hold 2500 rpm for one minute with the hood up.

   Look at

   Long-term fuel trim on bank 2 and whether any misfire counter climbs while you watch the screen.

   Fine if

   Trim stays inside plus or minus 10 percent and every misfire counter holds at zero.

   Broken if

   Trim climbs past plus 15 percent or a counter ticks upward. Fix that first, because a converter cannot survive a rich or misfiring engine.

   What you'll see A trim percentage that holds steady. Numbers that keep climbing mean the engine is still feeding the problem.

5. 5 If the front sensor failed step 1, replace it. Reach down behind the engine to the pipe, unplug the four-wire connector, then break the sensor loose with a 22mm socket.

   Look at

   Whether the code returns after the repair, watching the pending codes screen as well as stored codes.

   Fine if

   P0430 stays off through two cold starts and about 60 miles of mixed driving.

   Broken if

   The code returns within 30 miles with the new sensor fitted. The converter is then the remaining suspect.

   What you'll see The old sensor breaks free with a sharp crack. The new one turns in by hand for three turns before you need a wrench.

What the repair costs

Reference range compiled from 2 source type(s), as of 2026-11. This is not a quote — actual cost depends on your vehicle, region, and which part turns out to be the real cause.

Basis: reference · 2 source types cross-checked · Data as of 2026-11 · Confidence: medium

How to confirm it's really fixed

✓ Clear the code and run two full warm-up cycles with a cold start between them. If P0430 stays off after about 60 miles of mixed driving, the repair held. If it returns, test the converter before buying one.

Common questions