TSB110181-092914

Engine Speed Instability Related to Truck Vacuum Blower or Pump Engagement
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Technical Service Bulletin Number
TSB110181
Technical Service Bulletin
Subject
Engine Speed Instability Related to Truck Vacuum Blower or Pump Engagement
Issue
Some units have exhibited engine speed instability when the vacuum blower or pump is
engaged. This instability typically causes the operator to shut down the system. Some units
only exhibit this instability when the transmission is in an overdrive gear. New software added
a feature called Transmission Driven Power Take-Off (PTO) for ISX15 and ISX12
CM2250/CM2350 engines. This new software/feature can address most of these issues.
Verification
In order to properly test for instability; the unit must be operated with the transmission in an
upper gear, the transfer case engaged, and a load placed on the vacuum system.
1. If the unit displays vehicle speed on the dash during operation, most likely the
Transmission Driven PTO feature is not properly set up.
2. The truck body builder may have disabled the vehicle speed sensor (VSS) signal to the
engine control module (ECM).
3. The truck original equipment manufacturer (OEM) may have installed an additional PTO
switch that may be labeled “PTO Control”. This switch will disable the VSS signal to the
ECM.
4. Check that the ECM has the latest available calibration. Engines built prior to April 2011
were shipped with older calibrations.
5. Check for fault codes, including intermittent ones.
6. If the vehicle has a Parking Brake Switch input that is either wired directly to the ECM or
is multiplexed within, INSITE™ electronic service tool Parking Brake Switch must be
ENABLED.
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11/3/2014
Engine Speed Instability Related to Truck Vacuum Blower or Pump Engagement
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Resolution
1. Proper settings for Transmission Driven PTO:

 PTO - Maximum Vehicle Speed - 25 mph

 PTO - Alternate Operation - Enable

 PTO - Ignore Vehicle Speed Source in PTO - Disable

 PTO - Transmission Driven PTO - Enable

 PTO - Transmission Driven PTO - Transmission Driven PTO Type - Transmission
Driven - Irregular Load.
2. Proper settings for PTO:

 PTO - Maximum Engine Load - Backward calculate, using the manufacturer’s
torque rating for the PTO device and the gear ratio between the device and the
engine. Maximum Engine Load = Rated Torque/Gear Ratio.
3. Restore the VSS signal back to original factory condition. The VSS circuit should not be
interrupted. The ECM must read vehicle speed for the feature to work
4. Update the calibration if it is not up-to-date
5. Repair all fault codes.
If none of the above resolves the issue, dealers should contact Dealer Technical Support
(DTS) and distributors should contact the distributor technical support hotline or their distributor
Division Field Service Engineer (DFSE).
Warranty Statement
The information in this document has no effect on present warranty coverage or repair
practices, nor does it authorize TRP or Campaign actions.
Document History
Date
2011-6-14
2011-12-21
2012-2-27
2014-9-29
Details
Module Created
Information update
Updated Information
Adding additional engines which TSB is applicatable to
Last Modified: 02-Oct-2014
Copyright © 2000-2010 Cummins Inc. All rights reserved.
https://qsol2.cummins.com/qs3/pubsys2/xml/en/tsb/2011/tsb110181.html
11/3/2014