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Diagnostic trouble code

U0420

2 owner reports and 26 manufacturer filings across 15 model years from Chevrolet, Ford, Jeep, Lincoln and others.

NetworkGeneric OBD-II code26 manufacturer filings2 owner reports

Where U0420 shows up

Source: NHTSA manufacturer communications and complaints
Model yearFiled underBulletinsOwner reports
2019 Lincoln MKCElectronic Stability Control (Esc)4—
2025 Ford MustangEngine2—
2020 Mazda CX-9Electrical System2—
2019 Mazda CX-9Visibility2—
2018 Mazda CX-9Steering2—
2018 Mazda Mazda3Steering2—
2017 Mazda Mazda3Steering2—
2020 Mazda Mazda6Electrical System2—
2019 Mazda Mazda6Steering2—
2018 Mazda Mazda6Steering2—
2017 Mazda Mazda6Steering2—
2017 Chevrolet SSSteering—1
2026 Ford MustangEngine1—
2018 Jeep CompassElectrical System—1
2020 Mazda CX-5Electrical System1—

A model year appears here because the code is named in its record, not because every one of these vehicles sets it. Counts are mentions in the federal files, not failure rates — nobody publishes the denominator.

What it gets filed under

Steering 10Electrical System 6Service Brakes 3Forward Collision Avoidance 3Engine 2Unknown Or Other 1
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What owners said

Source: NHTSA complaint database

Owners’ own words, one per nameplate, scrubbed of anything identifying. These are unverified reports filed with NHTSA — they are what was said, not a finding that it was true.

I used my scanner to see what the codes are, and it have me a "Power Steering Control Module" C0800-03 code, as well as a "Keyless Entry" U0140, a "Parking Assist Module" U0420 code
2017 Chevrolet SSNov 22, 2024NHTSA owner report
Then my engine light went on and i had to have it towed to the nearest mechanic and when they checked the car had 4 codes P0123 P0222 P2111 and U0420
2018 Jeep CompassJul 15, 2022NHTSA owner report

Manufacturer filings that name it

Source: NHTSA manufacturer communications

Service bulletins and campaigns whose filed summary names U0420. Quoting the document number at a service desk is often the fastest route to a diagnosis someone has already written down.

What U0420 means

Source: SAE J2012 / OBD-II

U0420 sits in the generic range of the OBD-II standard, so it means the same thing on every vehicle sold in the United States — but WhichTrim does not carry a definition for it and will not invent one. What is on this page is the record: who named it and on what.

A stored code names the test that failed, never the part that caused it. It is the starting point of a diagnosis, not its conclusion — the same code has several possible causes and the cheap one is not always right.

Common questions about U0420

Source: NHTSA files and the OBD-II standard

Can I keep driving with U0420 stored?

Nobody can answer that from the code alone, and a site that does is guessing. A steady light generally means the fault was logged and the vehicle is in a reduced-risk mode; a flashing light means stop soon, because a misfiring engine can destroy a catalytic converter in minutes. The safe read of this page is the mileage and the components, not permission.

Does a code mean the car is recalled?

No. Recalls are filed by campaign and matched by VIN, and none of them are triggered by a scan tool. If you want to know whether an open recall applies to one specific vehicle, check the VIN at nhtsa.gov/recalls — that is the only source that settles it.

Why do the counts here differ from other sites?

Because these are not estimates. Every number on this page is a count of documents in NHTSA's own files: manufacturer communications that name the code in their filed summary, and owner complaints that name it in the narrative. We do not model, weight or extrapolate them.

Will clearing the code fix it?

Clearing turns the light off and erases the freeze-frame data a technician would have used to work out what happened. If the condition is still there the code returns, usually within a few drive cycles, and the diagnosis now starts from less information than before.