DIAGNOSTIC MANUAL
10.7. GRAPH 7: INVERTED EXHAUST GAS TEMPERATURES (INEFFICIENT DOC)
1. Diesel Oxidation Catalyst Inlet
Temperature (DOCIT) (degrees
Fahrenheit) [Red]
2. Diesel Particulate Filter (DPF) soot
load (percent) [Blue]
3. Diesel Oxidation Catalyst (DOC)
at operating temperature and
stabilized.
4. Diesel Particulate Filter Outlet
Temperature (DPFOT) (degrees
Fahrenheit) [Green]
5. Diesel Oxidation Catalyst Outlet
Temperature (DOCOT) (degrees
Fahrenheit) [Purple]
Figure 32
Graph 7: Inverted exhaust Gas Temperatures (Inefficient DOC)
Graph Analysis:
This graph shows inverted exhaust gas temperatures indicating an inefficient Diesel Oxidation Catalyst (DOC).
Inverted temperatures in the exhaust stream occur when the Diesel Particulate Filter Outlet Temperature
(DPFOT) is higher than Diesel Oxidation Catalyst Outlet Temperature (DOCOT) after the DOC has reached
operating temperature and stabilized (see callout 3, graph 7). This is caused by unburned fuel reacting with
the DPF, instead of the DOC, causing an increase in DPFOT. This test does not give pass or fail results. It only
allows the user to validate operation of the aftertreatment system by monitoring exhaust gas temperatures.
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