P0400 Code — Exhaust Gas Recirculation Flow Malfunction
P0400: Exhaust Gas Recirculation Flow Malfunction. This is a Powertrain trouble code — a generic OBD-II code that means the same thing on every make and model. Severity is generally Medium.
Have the vehicle scanned and the root cause confirmed before extended driving. Severity depends on the specific fault and symptoms.
What the P0400 code means
| Code | P0400 |
|---|---|
| Definition | Exhaust Gas Recirculation Flow Malfunction |
| System | Powertrain — engine, transmission and associated drivetrain systems |
| Code type | Generic (SAE J2012 standard) |
| Subsystem | Auxiliary emission controls |
| Fault reference | Fault #00 within the Powertrain group |
| Typical severity | Medium |
The letter P tells you the code belongs to the Powertrain family, covering engine, transmission and associated drivetrain systems. The second digit shows this is a standardized SAE code, so the definition above applies to any OBD-II compliant vehicle from 1996 onward. Within powertrain codes, it points to the auxiliary emission controls area.
Common causes of P0400
Because P0400 relates to the Powertrain system, likely culprits fall into these buckets. Confirm the actual fault with a scan before replacing parts:
- Faulty or aging sensors and their wiring in the affected circuit.
- Loose, corroded or damaged connectors and grounds.
- A failing component the code names directly (valve, solenoid, module or actuator).
- Related upstream issues — vacuum leaks, low fluids or a weak battery can trigger secondary codes.
How to fix a P0400 code
- Read and record the code with an OBD-II scanner, along with any freeze-frame data.
- Inspect the wiring, connectors and components in the Powertrain circuit the code points to.
- Repair or replace the confirmed faulty part — avoid swapping parts on a guess.
- Clear the code and drive a full cycle, then re-scan to confirm it does not return.
Recall repairs are free at a dealer, so it is worth checking for an open recall or decoding your VIN before paying for diagnostics — some faults are covered.
Related OBD-II codes
Frequently Asked Questions
What does P0400 mean?
P0400 is a Powertrain diagnostic trouble code that means: Exhaust Gas Recirculation Flow Malfunction. It is Generic (SAE standard) — the same meaning on every OBD-II vehicle.
Is it safe to drive with a P0400 code?
Have the vehicle scanned and the root cause confirmed before extended driving. Severity depends on the specific fault and symptoms.
How do I fix a P0400 code?
Confirm P0400 with an OBD-II scanner, inspect the components in the Powertrain system it points to, repair or replace the faulty part, then clear the code and re-scan to verify the fix. A professional diagnosis is recommended if you are unsure.
Code definition sourced from the open-source OBD-II code dataset (SAE J2012 / ISO 15031 standard). VinSpecs is an independent service and is not affiliated with any vehicle manufacturer.