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8

Perform a NOx Conversion Test and take screen captures.
INSTRUCTIONS
Read all the parts of step 8 to clearly understand the purpose of the test, know which part of the
graph curves you should monitor and be aware of the possible behaviors of the conversion test.
Note: It will be necessary to start the engine from the rear of the vehicle.
-----------------------------------------------Use this test to compare the inlet and outlet NOx sensor ppm levels. Usually we monitor the last
part of the test, just before shutdown, when the engine runs at high rpm (1800 rpm). Both levels
should be close to each other at that point. See the example below (image).
IMPORTANT NOTE: If the vehicle has the engine ECU software number 23470183 (see step 7),
the test will behave differently than what is shown in the example below. In this case, refer to NOx
Conversion Test With ECU software number 23470183.

USUAL BEHAVIOR

If both NOx sensor ppm levels are close to each other during the last part, as shown in the
example above (image), then both NOx sensors are good.
If ppm levels difference exceeds 10%, then the sensor reading higher should be considered as
defective.

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𝑝𝑝𝑝𝑝𝑝𝑝 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 (%) =

ℎ𝑖𝑖𝑖𝑖ℎ𝑒𝑒𝑒𝑒𝑒𝑒 𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣 − 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣
× 100
𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣

Ex.: 𝑝𝑝𝑝𝑝𝑝𝑝 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 (%) =

(288−279)
279

× 100 = 3.2 (%)

Are both original NOx sensors good (ppm difference ≤10%)? YES 

NO

ppm levels difference = ___________%
Replace the defective sensor 1 if applicable and then perform a new NOx sensor test once again
to make sure that the replacement sensor is good.
-----------------------------------------

NOx Conversion Test With engine ECU software number 23470183
Engine ECU software number 23470183 allows DEF dosing to continue during the last part of the
NOx conversion test (just before shutdown). This causes continued low outlet NOx sensor ppm
levels, as seen in the example below. Take screen captures.

DIFFERENT BEHAVIOR. In this example, the NOx sensors ppm levels are not close to each
other because DEF is still injected during the last part of the test. In this instance, review earlier
sections of the test to ensure that both sensors are responding to changes in the same manner.
Examples of different stages to review are shown below.

1

Change only one sensor, since both will eventually be replaced with the new SCR converter

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COMPARISON SHOULD BE DONE WHEN BOTH NOX SENSORS ARE
READING BELOW 600 ppm

The NOX sensors levels are close to each but earlier during the test (images above & below).

If both NOx sensor ppm levels are close to each other at a point during the test as shown in the
examples (image) above, then both NOx sensors are good.
If ppm levels difference is greater than 10%, then the sensor reading higher should be
considered as defective.
COMMENTS/RESULTS:
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9

If all of the five following conditions are satisfied, do not perform PART 2 of this bulletin.
Send this checklist along with screen captures to the Technical Publications to request approval
for the SCR converter replacement.
Conditions
1)
2)
3)
4)
5)

Engine is free from major component failure/performance issues
Five most recent SCR efficiency values hovering around or below 80% (step 2)
DEF dosing amount tests showed normal values (step 4)
DEF concentration within GOOD range (step 5)
Both original NOx sensors are good (step 8)

All five conditions satisfied, bulletin ended at step 9 (no need to perform sulfur regeneration nor a
road test):



Authorization for the replacement of the SCR converter. An analysis of this checklist with the
comments/results must be done in order to allow the replacement of the SCR converter. Scan and
send this checklist and all the relevant documents, photos, etc. to the Technical Publications
functional mailbox: technicalpublications_prev@volvo.com
Please indicate in the “subject line”: SP18-35 and the short V.I.N.
below…

as

in

the

example

COMMENTS/RESULTS:

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PART 2
#
1

checklist

INITIALS
AND
DATE

Perform one Sulfur Regeneration (Test screen 2589-08-03-02).

COMMENTS/RESULTS:
2

Do a test drive of at least 1 hour to 1 ½ hour at highway speed (45 minutes in each direction).

COMMENTS/RESULTS:
3

Connect PTT and take a screen shot of the last five (5) SCR efficiency evaluations (Test screen
2589‐08‐03‐05).
a) Make sure that the EMS has been able to carry out a new evaluation (see example
below showing the latest evaluation on top of the previous evaluations).
Note: It is very likely that a new evaluation cannot be carried out if the outside temperature
is rather cold during the road test. If this is the case, return the vehicle into service. Please
check the box below and indicate the outside temperature.

 EMS could not carry out a new evaluation

Outside temp: _____ °

b) If SCR efficiency value on the most recent evaluation is >85% vehicle may be released
(Typical new SCR is expected to get >90% SCR efficiency). This special bulletin can then
be closed. Please, Scan and send this checklist and all the relevant documents, photos,
etc.to the Technical Publications functional mailbox:
technicalpublications_prev@volvo.com.
c) Authorization for the replacement of the SCR converter. If post-road test SCR
efficiency value is less than 85%, an analysis of this checklist with the notes/results must
be done in order to allow the replacement of the SCR converter. Scan and send this
checklist and all the relevant documents, photos, etc. to the Technical Publications
functional mailbox: technicalpublications_prev@volvo.com
Please indicate in the “subject line”: SP18-35 and the short V.I.N. as in the example below…

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COMMENTS/RESULTS:

Example of SCR performance test
Before the road test

After the road test (most recent
evaluation=105%)

ADDITIONAL COMMENTSS/RESULTS:

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PARTS / WASTE DISPOSAL
Discard waste according to applicable environmental regulations (Municipal/State[Prov.]/ Federal)

WARRANTY
This diagnostic is covered by Prevost’s normal warranty. We will reimburse you the parts and labor upon receipt
of a warranty claim according to the following:
PARTS COVERED BY THIS BULLETIN
22677399

DEF injection nozzle gasket

Qty: 1

21376801

sealing plate

Qty: 1

Any other parts such as parts installed to correct exhaust leaks or for the replacement of sensors cannot
be charged to this bulletin. These are covered by the normal warranty when applicable and must be
charged on a different operation.
LABOR COVERED BY THIS BULLETIN
The time allowed to complete PART 1 of this bulletin is 2 hours
The time allowed to complete PART 1 & PART 2 of this bulletin is 4 ¼ hours
This allowed time covers the execution of the procedure described in this document only. Any corrective
work such as replacing the DEF injector, correcting exhaust leaks or any diagnostic work of active DTCs
codes other than P20EE is considered a separate operation on the repair order and cannot be charged
to this special bulletin.

Please submit claim via our Online Warranty System, available at www.prevostcar.com (under Service \
Warranty section). Use Claim Type: “Bulletin/Recall” and select ‘’Warranty Bulletin SP18-35 ".

Writer: EL

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Date
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OTHER
VBC Bulletin

N/A

Fail Code

04.04-1

Defect Code

9

Syst. Cond

B

Causal Part

21970125

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Access all our Service Bulletins on

http://techpub.prevostcar.com/en/
or scan the QR-Code with your smart phone.

Prevost engages in a continuous program of testing and evaluating to provide the best possible product. Prevost, however, is not committed
to, or liable for updating existing products.

Writer: EL