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Released: 03-29-2012 SU1201

Models Affected: All Products with EPA 2010 Cummins SCR-DEF System.

The EPA mandated 2010 Cummins SCR system was implemented last year. While many buses equipped with this new system performed as designed, there were some issues in the field related to this new design. This update will share the corrective actions that we are aware of pertaining to issues experienced this past year.

In order to learn more about cold weather related issues, a Blue Bird Engineering team as well as members of our engine and DEF tanks suppliers conducted cold weather testing at Bergstrom's Environmental Chamber in Rockford, Illinois during the week of July 25‐28, 2011. The purpose of the test was to evaluate potential causes of cold‐weather related engine fault codes experienced by customers during the 2010‐2011 winter season, for vehicles equipped with the EPA 2010 Cummins SCR‐DEF system. The results of the testing showed that the system works as designed when all sub‐components are functioning properly. By design, the system allows up to 70 minutes to thaw before any codes are displayed. If the unit cannot dose after 70 minutes, codes and/or buzzers will appear and the bus will begin to de‐rate.

The following are issues that we experienced related to the SCR system and the corrective actions that have been implemented:

1. Fault code of 1679 and/or 3651. Early production of 2010 Cummins SCR‐DEF system buses contained some faulty DEF tank temperature sensors which prevented the DEF from thawing and the SCR system from priming for DEF dosing. This resulted in a common fault code of 1679 and/or 3651. This caused an un‐erasable/un‐resettable fault code that could only be resolved with a complete re‐calibration of the ECM. This temperature sensor issue within the DEF tank was corrected in January 2011 with any DEF head with a serial number greater than 7775.

2. Fault code of 3596. The root cause of the 3596 codes is a cracked suction tube in the DEF tank head assembly suction tubes. Our DEF tank supplier has completely redesigned this area of the def tank head assembly to eliminate this issue. This change was implemented in July of 2011. The tank heads with new suction tubes are identified by a serial number greater than 23505. All shipments to Blue Bird after 7/13/2011 have the new design.

3. Fault Code 3597.The root cause of 3597 codes is low voltage. Hi‐Idle MUST be used when heaters or air conditioning is being used to keep the electrical output high. Alternator charging capacity, at 800 rpm "curb idle," is insufficient for extreme‐cold conditions. With proper voltage there were no DCU to ECM communication faults activated.

4. Fault Code 3597. Cummins issued TSB110117 which increases the time so that the DCU would be less sensitive to battery voltage fluctuations. See your Cummins dealer for the proper calibration if your engine was produced prior to June 2011.

5. Fault Code 3582- There is an update to the diagnostics so the ECM would prevent flagging false catalyst efficiency faults due to ammonia slip. See your Cummins dealer with capability of changing the ECM calibration for this update.

6. Fault Code 3543-The diesel exhaust fluid quality is not sufficient enough to provide adequate NOx reduction. See your Cummins dealer and have campaign C1166 performed.

7. Service Memorandum SM1109‐ DEF Reservoir Overfill Protection‐ See Service Memorandum SM1109 for instructions on proper filling levels for the DEF reservoir.

8. Service Bulletin S11TL‐D3RE DEF Tank Level Sensor Replacement. On certain model D3RE’s, the Diesel Exhaust Fluid (DEF) tank level sensor did not read accurately on the tank fluid level gauge. See S11TL for replacement instructions.

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