P0400
2 owner reports and 30 manufacturer filings across 30 model years from Hyundai, Mitsubishi, Subaru.
Where P0400 shows up
Source: NHTSA manufacturer communications and complaints| Model year | Filed under | Bulletins | Owner reports | Parts |
|---|---|---|---|---|
| 2017 Subaru Legacy/Outback | Electrical System | 2 | — | Battery → |
| 2016 Subaru Legacy/Outback | Engine | 2 | — | |
| 2023 Hyundai Tucson | Electrical System | — | 1 | Battery → |
| 2022 Hyundai Tucson | Engine | — | 1 | |
| 2023 Mitsubishi Outlander | Engine | 1 | — | |
| 2022 Mitsubishi Outlander | Engine | 1 | — | |
| 2021 Mitsubishi Outlander | Engine | 1 | — | |
| 2020 Mitsubishi Outlander | Engine | 1 | — | |
| 2019 Mitsubishi Outlander | Engine | 1 | — | |
| 2020 Subaru Crosstrek | Engine | 1 | — | |
| 2019 Subaru Crosstrek | Electrical System | 1 | — | Battery → |
| 2018 Subaru Crosstrek | Engine | 1 | — | |
| 2017 Subaru Crosstrek | Engine | 1 | — | |
| 2016 Subaru Crosstrek | Electrical System | 1 | — | Battery → |
| 2020 Subaru Forester | Engine | 1 | — | |
| 2019 Subaru Forester | Engine | 1 | — | |
| 2018 Subaru Forester | Engine | 1 | — | |
| 2017 Subaru Forester | Electrical System | 1 | — | Battery → |
| 2016 Subaru Forester | Electrical System | 1 | — | Battery → |
| 2020 Subaru Impreza | Engine | 1 | — | |
| 2019 Subaru Impreza | Engine | 1 | — | |
| 2018 Subaru Impreza | Engine | 1 | — | |
| 2017 Subaru Impreza | Electrical System | 1 | — | Battery → |
| 2016 Subaru Impreza/Outback Sport | Engine | 1 | — | |
| 2020 Subaru Legacy | Engine | 1 | — |
Showing the 25 model years where P0400 appears most; it is on file for 30 in total.
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.
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P0400 by make
The same record, one make at a time: the model years, bulletins and owner reports that name P0400 on that maker’s vehicles.
What it gets filed under
What owners said
Source: NHTSA complaint databaseOwners’ 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.
Diagnostic & Technical Details: Error Codes Captured: Diagnostic trouble codes in the P0400 series (EGR system flow/circuit malfunction) along with connector/wiring degradation were confirmed during inspection
30 manufacturer filings name P0400. Start with what the maker wrote down.
A code names the test that failed, not the part. A bulletin that names it is often a diagnosis someone has already written down — quote its number at the service desk.
Manufacturer filings that name it
Source: NHTSA manufacturer communicationsService bulletins and campaigns whose filed summary names P0400.
- TSB-23-13-004 Service bulletin2023-08-02 · Engine And Engine Cooling
- This Technical Service Bulletin provides instructions to reprogram the ECU with the countermeasure software when the check engine light illuminates with DTC of P0401/ P0400.
- 11-200-20R Service bulletin2020-05-06 · Engine And Engine Cooling — Exhaust System — Emission Control
- This bulletin announces the availability of reprogramming files to optimize the Engine Control Module (ECM) for hard starting in sub-freezing temperatures, DTC P0400, and surging in high altitudes.
- 11-197-20 Service bulletin2020-02-11 · Engine And Engine Cooling
- This bulletin announces availability of reprogramming files to optimize the Engine Control Module (ECM). These new files address concerns of the check engine light coming on and setting a DTC P0400: EGR “A” FLOW. The DTC can set if the ECM tests the EGR system when ambient / intake air temperatures are below freezing.
What P0400 means
Source: SAE J2012 / OBD-IIP0400 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 P0400
Source: NHTSA files and the OBD-II standardCan I keep driving with P0400 stored?
Nobody can answer that from the code alone, and a site that does is guessing. A steady light means a fault was logged and the car should be checked soon; a flashing light means a severe misfire — slow down and get it seen as soon as possible, because severe misfire can quickly damage the catalytic converter. 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.