SPN 651
CAUTION
Injector cylinder 1
The truck's control module (ECU) reports a fault on: Injector cylinder 1.
SPN 651 means a truck control module (ECU) flagged a fault on injector cylinder 1, part of the Fuel system on heavy-duty diesel trucks. DERATE rates it CAUTION: you can keep driving carefully, but get it checked soon. Part usually replaced: Fuel injector (one), $350–$1,200 (aftermarket to dealer) plus 2–4 h labor.
Fuel
Can I keep driving?
Yes, carefully. It does not usually cut power, but get it checked soon.
Part usually replaced
Fuel injector (one)
$350–$1,200 (aftermarket to dealer)
Labor: 2–4 h
Price per injector; a set is 6×
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.