SPN 5571
CAUTION
DEF high pressure relief
The truck's control module (ECU) reports a fault on: DEF high pressure relief.
SPN 5571 means a truck control module (ECU) flagged a fault on DEF high pressure relief, part of the SCR / DEF system on heavy-duty diesel trucks. DERATE rates it CAUTION: you can keep driving carefully, but get it checked soon. Part usually replaced: DEF pressure line / relief valve, $120–$600 (aftermarket to dealer) plus 1–2.5 h labor.
SCR / DEF
Can I keep driving?
Yes, carefully. It does not usually cut power, but get it checked soon.
Part usually replaced
DEF pressure line / relief valve
$120–$600 (aftermarket to dealer)
Labor: 1–2.5 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.