Exhaust Gas Recirculation Flow Malfunction
The engine computer found that exhaust gas recirculation flow did not respond as expected. P0400 is a general flow malfunction and does not by itself specify insufficient or excessive flow. Restricted passages, the valve, control system or feedback measurement may be involved. EGR designs vary, so the code alone is not a reason to clean or replace a valve.
Can I keep driving?
If the engine stalls, the light flashes, shaking is severe, or power loss makes traffic unsafe, pull over safely and arrange towing. With a steady light and normal operation, ask a shop for advice based on symptoms before further driving.
What does this code mean for your car?
The same code can need different checks depending on the model and engine. Enter your vehicle details to find relevant sources and checks.
Symptoms
- Check engine light
- Unstable idle or stalling in some cases
- Hesitation or reduced response
Possible causes
- 1Restricted or leaking EGR passages
- 2EGR valve not moving as required
- 3Vacuum control or electrical actuation problem
- 4Inaccurate pressure, flow or position feedback
These possibilities are not ranked by frequency and do not diagnose your vehicle.
Checks you can safely do yourself
Safe checks only: engine off and cold, car on level ground.
- Save the code and freeze-frame data if your scanner offers them, without clearing anything.
- With the engine off and cool, look at accessible hoses and wiring for obvious damage without removing the EGR assembly or using cleaning chemicals.
When you need a shop
Stop and arrange towing for stalling, severe shaking or unsafe power loss. Diagnosis should compare the EGR command with feedback, test wiring and actuation, and inspect the flow path as indicated for that engine.
How much does it cost?
A US repair estimate needs a diagnosis and a local shop quote.
No verified US repair quote is available for this fault. The price depends on diagnosis, vehicle, parts and local labor; request 2-3 itemized quotes.
Get 2-3 quotes
Investigate this code for my carFAQ
Can I keep driving with P0400?
If the engine stalls, the light flashes, shaking is severe, or power loss makes traffic unsafe, pull over safely and arrange towing. With a steady light and normal operation, ask a shop for advice based on symptoms before further driving.
What can cause P0400?
Possible causes include restricted or leaking EGR passages; eGR valve not moving as required; vacuum control or electrical actuation problem; inaccurate pressure, flow or position feedback. These are diagnostic possibilities, not a confirmed diagnosis or a parts shopping list.
Does clearing the code fix the problem?
No. Clearing a code does not repair the problem or prove that no fault exists. It may erase useful evidence and reset readiness monitors. Save codes and freeze-frame data first; confirming a repair requires the vehicle-specific checks.
What if this code appears during a used-car inspection?
Arrange an independent professional pre-purchase inspection before committing. Request a complete scan, readiness status and diagnosis of the relevant system. Get written findings and a repair estimate; an unlit warning lamp does not replace inspection.
How much does a P0400 repair cost?
No verified US repair quote is available for this fault. The price depends on diagnosis, vehicle, parts and local labor; request 2-3 itemized quotes.