DIAGNOSTIC MANUAL
9.6. SYMPTOM 5 (HEAVY DUTY): BLACK SMOKE
OVERVIEW: Hydrocarbon slip occurs when diesel fuel does not fully combust in the aftertreatment
system and slips through the DPF into the clean side of the exhaust. Hydrocarbon slip is associated
with high idle time. The DPF should NOT be replaced due to black staining in the exhaust.
NOTE – The Diesel Particulate Filter (DPF) is not 100 percent efficient. Some evidence of exhaust soot
is normal, and does not indicate a malfunctioning DPF.
WARNING
To prevent unexpected movement of the vehicle and possible injury or death, park the
vehicle on a flat, level surface, apply the parking brake, turn the engine off and chock the
wheels to prevent vehicle from moving in either direction.
NOTE – Before beginning the following step-based diagnostics, perform all vehicle operational checks
page 80.
Step
Action
Decision
1
Diesel Particulate Filter ( DPF) Snap Acceleration Test
(Quick Test). This procedure checks the DPF for cracks
or internal damage without removing the DPF from the
vehicle and is used to test basic functionality of the DPF.
This is to be done prior to removing the DPF.
1.
The transmission must be in neutral and the
parking brake applied.
2.
Start and idle the engine.
3.
Rapidly snap the accelerator pedal from
idle to full throttle. This can be performed
multiple times.
4.
During the engine accelerations, visually
check for a heavy black smoke exiting the
exhaust pipe.
Is black smoke visible?
Yes: Go to step 2
End of diagnostics
113
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