P0400 on Subaru vehicles
P0400 is named on 23 Subaru model years (2016–2020): 25 manufacturer filings and 0 owner reports in NHTSA’s files, across Legacy/Outback, Crosstrek, Forester, Impreza, Impreza/Outback Sport and 2 more.
Which Subaru model years name P0400
Source: NHTSA manufacturer communications and complaints| Model year | Filed under | Bulletins | Owner reports |
|---|---|---|---|
| 2017 Subaru Legacy/Outback | Electrical System | 2 | — |
| 2016 Subaru Legacy/Outback | Electrical System | 2 | — |
| 2020 Subaru Crosstrek | Electrical System | 1 | — |
| 2020 Subaru Forester | Engine | 1 | — |
| 2020 Subaru Impreza | Electrical System | 1 | — |
| 2020 Subaru Legacy | Electrical System | 1 | — |
| 2020 Subaru Outback | Engine | 1 | — |
| 2019 Subaru Crosstrek | Electrical System | 1 | — |
| 2019 Subaru Forester | Electrical System | 1 | — |
| 2019 Subaru Impreza | Engine | 1 | — |
| 2019 Subaru Legacy | Electrical System | 1 | — |
| 2019 Subaru Outback | Electrical System | 1 | — |
| 2018 Subaru Crosstrek | Electrical System | 1 | — |
| 2018 Subaru Forester | Electrical System | 1 | — |
| 2018 Subaru Impreza | Electrical System | 1 | — |
| 2018 Subaru Legacy | Electrical System | 1 | — |
| 2018 Subaru Outback | Engine | 1 | — |
| 2017 Subaru Crosstrek | Engine | 1 | — |
| 2017 Subaru Forester | Engine | 1 | — |
| 2017 Subaru Impreza | Engine | 1 | — |
| 2016 Subaru Crosstrek | Electrical System | 1 | — |
| 2016 Subaru Forester | Electrical System | 1 | — |
| 2016 Subaru Impreza/Outback Sport | Engine | 1 | — |
A model year is listed because the code is named in its own record — a bulletin filed against it, or an owner’s complaint about it — not because every one of these vehicles sets it. Counts are documents in NHTSA’s files, not failure rates.
Subaru filings that name P0400
Source: NHTSA manufacturer communicationsBulletins and campaigns Subaru filed with NHTSA whose summary names P0400. Quote the document number at the service desk — it is a diagnosis the maker has already written down.
- 11-200-20R Service bulletin2020-05-06 · Electrical System — Software
- 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. The record above is what Subaru and its owners have filed about it; the code’s page across every make has the whole file.
Common questions
Source: NHTSA files and the OBD-II standardIs P0400 a known problem on Subaru vehicles?
It is a documented one: NHTSA's files hold 25 manufacturer filings and 0 owner reports naming P0400 on 23 Subaru model years (2016–2020). Whether it is a problem on one particular car is a diagnosis, not a count — but a bulletin that names the code on your model year is the place to start.
Which Subaru models does P0400 appear on most?
2017 Legacy/Outback (2 documents), 2016 Legacy/Outback (2 documents), 2020 Crosstrek (1 document).
Does P0400 on a Subaru mean it is recalled?
No. Recalls are filed by campaign and matched by VIN; no recall is triggered by a scan tool. Check the VIN at nhtsa.gov/recalls, or open the model year's page here for the campaigns filed against it.