P0401
CAUTION
EGR flow insufficient
The truck's control module (ECU) reports a fault on: EGR flow insufficient.
P0401 means a truck control module (ECU) flagged a fault on EGR flow insufficient, part of the EGR system on heavy-duty diesel trucks. DERATE rates it CAUTION: you can keep driving carefully, but get it checked soon. Part usually replaced: EGR valve, $350–$1,400 (aftermarket to dealer) plus 2–4 h labor.
EGR
Can I keep driving?
Yes, carefully. It does not usually cut power, but get it checked soon.
Part usually replaced
EGR valve
$350–$1,400 (aftermarket to dealer)
Labor: 2–4 h
USD, part only. Labor is billed at the shop's hourly rate.
Data: DERATE verified base, updated October 2026
Related codes
Read it off your own dash
Take one photo and DERATE tells you whether you can keep driving.
Ask DERATE
DERATE assists. It does not replace inspection by a qualified technician.