Service Update

SU2201: DEF Diagnostics for CAN Sensors

Models Affected: Certain Blue Bird Buses equipped with Cummins Diesel engines built starting
Jan 2016 with the below engine families:
•
•
•
•
•
•
•

B6.7 CM2350 B121B (Excluding engines built in 2021)
B6.7 CM2450 B155B
ISB6.7 CM2350 B101 (Engines built in 2016 only)
ISL9 CM2350 L101 (Engines built in 2016 only)
L9 CM2350 L116B
L9 CM2350 L123B
L9 CM2450 L126B

Subject: Blue Bird specific troubleshooting required for Cummins TSB210187.
WARNING: Always follow all Federal, State, Local and Shop safety standards and use proper
safety equipment, and thoroughly read and understand all instructions before performing these
procedures. Park bus on level surface, apply parking brake, turn off ignition key, and chock
wheels.
Summary: This document is intended to provide guidance to the specific diagnostic procedures
required by Blue Bird to install an available temporary engine calibration to allow unit operation
during repair parts procurement. A unique authorization code is assigned to each ESN. Contact
your local Blue Bird dealer to verify part availability and obtain an authorization code, if
applicable.
To find your local Blue Bird dealer, go to www.Blue-Bird.com/Find-a-Dealer
Diagnostic Procedure:
• Review the below flow charts for troubleshooting DEF sensor fault codes. For
troubleshooting DTC’s not listed in one the below flow charts, follow Cummins published
troubleshooting documents per the applicable workshop manual.
• If the Blue Bird diagnostic flow chart(s) identifies the DEF sensor assembly is inoperative,
and service parts are unavailable, the Blue Bird dealer is REQUIRED to submit a technical
support ticket via vantage and request a unique authorization code.
• If this unit is being repaired at an authorized Cummins repair facility, the locations are
REQUIRED to contact their local Blue Bird dealer and request they submit a technical
support ticket via Vantage and request a unique authorization code.
• ECM image is highly recommended to be attached to support ticket for faster processing. If
an image is not available, detailed diagnostics and supporting details around fault code
timing will be requested. Lack of supporting diagnostics may result in denial of an
authorization code request.

Once pre-authorization is obtained, email must be sent to T2484@cummins.com with the
following items:
1) evidence pre-authorization was received,
2) ESN,
3) OEM,
4) current ECM code
NOTE: A diagnostic scan tool MUST be used for diagnostics. The instrument cluster does not
provide the level of needed detail to objectively determine the failure(s). Failure to diagnose will
result the in the vehicle illuminating the MIL/amber engine warning after the new sensor/head has
been installed and the calibration reverted back to OEM.
Parts Required:
Qty
1
2

Blue Bird #
10078848
NA

Description
CAP,CONNECTOR
Wire tie (obtain locally)

Protective cover will be provided by Blue Bird dealers at no cost to repair centers. Blue Bird
dealers can order them as needed thru standard parts channels and claim on warranty repairs.
Wire ties to be sourced locally.
1. Key off, cut Ty-wrap(s) and disconnect DEF sensor.
2. Install cover 10078848 onto the frame harness and secure harness end with wire tie. Bend
the DEF header harness away from the OE chassis harness and secure with wire tie.
NOTE: Cummins TSB210187, step 3 states to cut the pig tail off of the DEF sensor header while
the calibration is downloading. DO NOT CUT THE BLUE BIRD DEF SENSOR PIGTAIL. The
cavity plug installed on step 2 is sufficient. Damaging the DEF sensor pigtail or connector may
result in warranty charge backs.
3. Acquire Fleet count for InSite tool to be used and use the ECM code lookup tool listed

below to identify the proper code for the effected bus(s).
https://quickserve.cummins.com/qs3/qsol/service/def_header_ecm_tools.html
4. Install temp ECM calibration. Follow Cummins workshop manual for additional
information/instruction if needed.
5. Disregard Cummins TSB210187 steps 4-8
6. Verify new Cummins Engine Calibration is installed.
7. Required to submit for remittance via Cummins TRP2484.

Service Update

SU2201: DEF Diagnostics for CAN Sensors
FAULT CODES 3868, 4677, AND 4572 ALL CURRENTLY ACTIVE
WITH NO OTHER CODES (EXCLUDING TORQUE REDUCTION
CODES)?

NO

ARE FAULT CODES 3868, 4572, AND 4677
CURRENTLY INACTIVE AND ALL THREE HAVE THE
SAME INACTIVE COUNTS(+- 1)?

YES

AFTER ENGINE START, UNPLUG DEF TANK SENSOR
CONNECTOR. PAUSE 10 SECONDS, THEN RECONNECT.
IDLE ENGINE FOR 1 MINUTE. DO 3868, 4677, AND 4572
GO INACTIVE(ENGINE WARNING GOES OUT, MIL STAYS
ON)?

YES
CHARGE AND TEST BATTERIES INDIVIDUALLY. ALL THREE
PASS?

YES

NO
YES

NO

KOEO, WITH SENSOR CONNECTED,
MEASURE(BACKPROBE) VOLTAGE BETWEEN PINS 3 AND
4. IS VOLTAGE >10 VOLTS?

NO

SAVE INSITE ECM IMAGE IN
.EIF FORMAT. CREATE
SUPPORT TICKET VIA VANTAGE
AND ATTACH FOR
ESCALATION.

YES
REPLACE BATTERY(S) AS
NEEDED AND RE-TEST
NO
NO

KOEO, WITH SENSOR CONNECTED,
MEASURE VOLTAGE(BACKPROBE)
BETWEEN PINS 1 AND 3. IS VOLTAGE
BETWEEN 1.5 AND 2.3 VOLTS?

SERVICE HARNESS AS REQUIRED.
ENGAGE BLUE BIRD FIELD SERVICE FOR
ASSISTANCE
PERFORM A/T HARNESS MODIFICATION.
FOLLOW SI 35-300-131 EXACTLY. NO
DEVIATIONS APPROVED. HARNESS MUST BE
RAN TO BATTERIES ONLY!

KOEO, WITH SENSOR CONNECTED
MEASURE(BACKPROBE) VOLTAGE BETWEEN
PINS 2 AND 3. VOLTAGE 2.5-3.5 VOLTS?

NO

NO

DISCONNECT DEF SENSOR. DOES
VOLTAGE MOVE TO WITHIN PROPER
LIMITS?

NO

YES

DEF SENSOR ASSY HAS FAILED. ARE
SERVICE PARTS AVAILIBLE?

NO

YES

YES

REPLACE DEF SENSOR ASSY

YES

NO

YES

KOEO, AT 3-PIN ENGINE DATALINK CONNECTOR, SNIFF
J1939(500K/CUMMINS PRIVATE) CAN FOR
0xA3_FC31, FD35, AND FD36 MESSAGES.
ARE MESSAGES PRESENT
(SELECT NO IF UNABLE TO VERIFY)?

Service Update

SU2201: DEF Diagnostics for CAN Sensors

FAULT CODES 3868, 4677, 4572, 3232, 2771,
6688, 4151, AND 3868 ALL CURRENTLY ACTIVE
WITH NO OTHER FAULT CODES(EXCLUDING
TORQUE DERATE CODES)

NO

DOES THE AFTERTREATMENT IGN FUSE HAVE 12 VOLTS
ON EACH SIDE?

YES

NO

YES

SPECIFIC LIST OF CODES ALL CURRENTY INACTIVE,
SIMILAR COUNTS, WITHIN 1 ECM MINUTE OF EACH
OTHER, AND LESS THAN 20 ECM HOURS OLD?

YES

REMOVE A/T RELAY. ARE WITNESS
MARKS PRESENT ON RELAY
TERMINALS?

IS THE UNIT EQUIPPED WITH AN
A/T RELAY?

YES

REPLACE FUSE AND T/S
HARNESS FOR OVER
CURRENT CONDITIONS

NO

NO
YES
NO ACTION REQUIRED. WANT TO
ESCALATE?

NO

REPLACE SOCKET PINS
AS NEEDED
REPLACE AS NEEDED

REPLACE RELAY.
FAULTS STILL ACTIVE?

NO
NO

YES

YES
SAVE INSITE IMAGE IN .EIF
FORMAT. CREATE SERVICE
TICKET VIA BLUE BIRD
VANTAGE AND ATTACH
IMAGE FOR ENGINEERING
REVIEW

YES

ARE >10 VOLTS AND
GROUND PRESENT ON ALL
EFFECTED COMPONENTS?
NO

NO

INSPECT HARNESS FOR DAMAGE/
FAILURE. PROBLEM IDENTIFIED?

YES

PERFORM 10 ENGINE STARTS.
FAULTS RETURN?

CHARGE AND TEST
BATTERIES INDIVIDUALLY.
ALL CHECK OK?

YES

PERFORM THE A/T REWIRE INSTRUCTIONS

NO

COMPLETE

Service Update

SU2201: DEF Diagnostics for CAN Sensors