For professional technicians and shop owners

From error code to
ranked part list.
Confidence included.

Enter a DTC. Get a probability-ranked list of likely causes — with global vendor pricing and availability for every part. Stop guessing. Start fixing.

P0420 P0171 P0300 P0442 +5,000 more
PartRank — DTC Lookup
DTC
P0420
Code P0420 — Catalyst System Efficiency Below Threshold
1
Catalytic Converter Bank 1, primary converter failure
73%
2
O2 Sensor — Post Cat Bank 1 Sensor 2, degraded reading
18%
3
O2 Sensor — Pre Cat Bank 1 Sensor 1, false lean reading
7%
4
Exhaust Leak Upstream of converter, false air
2%
73% of P0420 diagnoses are the catalytic converter
5,400+ DTCs covered across all vehicle systems
50+ global parts vendors indexed for pricing
What you get

Not a list of possibilities.
A ranked diagnosis.

Probability-ranked parts

Every DTC returns a weighted list of likely causes, sorted by real-world repair frequency and vehicle-specific data. Top result first — no more guessing which of ten possibilities it is.

Real-time vendor pricing

Every listed part links to live pricing from AutoZone, O'Reilly, RockAuto, Amazon, and distributors worldwide. See availability in your region. Order in one click.

All vehicle types

OBD-II passenger vehicles, medium-duty trucks, Class 4-8 commercial trucks, and heavy equipment. One interface, every system in your shop.

Confidence percentage, not a guess

Each ranked part shows a percentage derived from millions of real repair records — not guesswork. When a tech walks into a job, they know what to check first.

The problem with current tools

Every scan tool tells you
what the code means.
None tells you what
to fix first.

A P0420 means the catalytic efficiency dropped. Great. But is it the converter, the O2 sensors, an exhaust leak, or a wiring issue? Every tool gives you the same list of five possibilities and leaves you to figure out which one.

PartRank uses repair record data from hundreds of thousands of jobs to rank those possibilities by likelihood. P0420 on a 2012 Honda? 73% it's the converter. P0420 on a 2018 Ram? The O2 sensors lead at 41%.

This is what a smarter diagnostic tool looks like
P0420 — Catalytic Converter Efficiency Passenger vehicles, 2000–2025
Standard tool
Catalytic converter failure
O2 sensor malfunction (bank 1 sensor 1)
O2 sensor malfunction (bank 1 sensor 2)
Exhaust leak before converter
Fuel system too rich or lean
PartRank
73% Catalytic converter
18% O2 sensor, post-cat
7% O2 sensor, pre-cat
2% Exhaust leak
<1% Fuel system
Vehicle coverage

One lookup. Every
system on the lot.

Passenger vehicles
OBD-II, all makes 1996–present
Medium & light duty trucks
Class 1–3, all makes
Heavy commercial trucks
Class 4–8, J1939 protocol
Heavy equipment
Off-road, agriculture, construction
Coming soon — get early access

The check engine light
stops being a guessing game.

PartRank turns one DTC into a ranked diagnosis, real parts pricing, and a path to the fix — in under five seconds.

5,400+ DTCs indexed
50+ Vendors worldwide
99% Vehicle coverage