6/30/23, 12:58 PM

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Volvo Selective Catalytic Reduction (SCR) Muffler
Troubleshooting Guide - US10+OBD13 And Newer
Emissions
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Component Overview
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The SCR contains a coated substrate that, with the input of heat and DEF,
changes NOx into nitrogen and water vapor. The SCR's job in the Emissions
After-Treatment System (EATS) is to lower the NOx level emitted into the
atmosphere.
The performance of the SCR is evaluated by the NOx sensors. There are
NOx sensors that are located on upstream (inlet) and downstream (outlet)
ends of the SCR.
Important: the SCR is the last component in the EATS which makes
it susceptible to any upstream failures.

Primary failure mode of the Muffler (SCR) is:
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Coating of the substrate being compromised
Indigestions of foreign objects such as oil, coolant, fuel, etc.

Diagnosis and Repair
Prior to proceeding with any of the information below, any codes,
symptoms or failures of upstream components must be diagnosed and
corrected first.
Upstream components include:
Base Engine (Starting or operation issues)
EGR System
Fuel System (Engine supply and aftertreatment hydrocarbon injector
supply)
Turbocharger/Boost
Diesel Oxidation Catalyst (DOC)
Diesel Particulate Filter (DPF)
Aftertreatment sensors (Exhaust temperature)

The three DTCs below indicate problems with SCR function. These DTCs
should only be diagnosed if they are active or if the DTC Confirmed status is
True in the Detailed status information section.

Fault
Code

Descriptions

P20EE

SCR NOx Catalyst Efficiency Below Threshold (Bank 1)

P103C

NOx Catalyst Efficiency Inducement, Selective Catalytic
Reduction (SCR) Unit

P207F

SCR NOx Catalyst Efficiency Below Threshold (Bank 1)

Evaluations for SCR Muffler Replacement
The following systems need to be evaluated in progressive order to
determine the state of the SCR.
1. DEF System - Test the Urea/DEF Systems functionality for proper:
Quality
Check DEF Quality using Refractometer (88890105)
Litmus Test paper (88890110)
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Quantity
SCR Dosing Test in PTT, Operation 2589-08-03-05
subsection 1-3.
With the dosing nozzle removed, inspect for crystal build up.
If any of the above tests fail: Correct the issue, clear fault codes, and
release the truck.

2. NOx Sensor Condition - Evaluate the condition of both NOx
Sensors.
Look for the following:
Non-OEM (3rd party) sensors, use CBR-2114 for guidance.
Any/All NOx sensor fault codes. See CBR-2116 for a list of
these faults and recommendations.
If Non-OEM or faulty Nox Sensor(s) is found: Replace the sensor(s),
clear faults and release the truck.

3. NOx Sensor Function and SCR Assessment- Evaluate NOx sensor
function using the appropriate test for the vehicle's emission level,
indicated below. Follow the directions in the Action column for Nox or
SCR Replacements.
Emission
Level

PTT Operation

Action

OBD 13-16

2549-08-03-03 Nox
Conversion Test

Follow test recommendation, if no
fault found replace the SCR in
accordance with Impact
procedures.

OBD 17 to
current

2589-08-03-18
Exhaust
Aftertreatment
System Analysts

Follow test recommendation and
release truck.

or
2549-08-03-03 NOx
conversion test below
EATS annalysis
OBD 17-18
TC Only

No test…

Replace Both Nox Sensors if not
replaced within past 3 months
and release truck. If truck has
received both Nox sensors within

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past 3 months replace the SCR in
accordance to impact
procedures.

Rules for Replacement
Standard Diagnostic time is 3 hours.
Note that Warranty will only cover replacement of the SCR if one of the
three codes in the section above is present. If the SCR is suspected to
have failed due to upstream contamination with no codes present, an
eService case is required for further evaluation.

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p103c00

p207f00

volvo

scr

p20ee00

unlocking uptime
Categories
Make and Model > Volvo > VNL
Make and Model > Volvo > VNR
Make and Model > Volvo > VNM
Make and Model > Volvo > VNX
Make and Model > Volvo > VAH
Make and Model > Volvo > VHD
Vehicle System > Emissions

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