TSB110181-031416

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, with transfer cases, 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 engine control module (ECM) software added a feature called Transmission Driven
Power Take-Off (PTO). This new ECM software/feature can address most of these issues.
Verification
Product Affected:





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ISX15 CM2250
ISX15 CM2250 SN
ISX15 CM2350 X101
ISX12/ISX11.9 CM2250
ISX12 CM2350 X102
ISL9 CM2350 L101
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 engine.
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
ECM.
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Engine Speed Instability Related to Truck Vacuum Blower or Pump Engagement
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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.
NOTE: If the vehicle does not have a parking brake switch input, then the OEM or body
builder must install the governor type switch to indicate to the ECM when the transfer
case is engaged.
Resolution
1. Proper settings for Transmission Driven PTO:
 PTO - Alternate Operation - Enable (Recommended for fire trucks and vacuum
trucks only)
 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. Ensure the VSS circuit is not
interrupted. The ECM must read vehicle speed for the feature to work.
4. Update the ECM calibration if not already up-to-date.
5. Repair all fault codes.
If none of the above resolves the issue, contact your authorized Cummins® repair location. For
authorized Cummins® repair locations, follow your technical support escalation process.
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
Details
Module Created
Updated Information.
Updated Information.
https://quickserve.cummins.com/qs3/pubsys2/xml/en/tsb/2011/tsb110181.html
4/5/2016
Engine Speed Instability Related to Truck Vacuum Blower or Pump Engagement
2014-9-29
2015-4-22
2016-3-14
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Additional engines added.
Additional engines added.
Added statement about transfer cases, note about parking brake switch input,
and recommendation for fire trucks and vacuum trucks only. Changed
reference about placing a load on the engine vacuum system to placing a load
on just the engine.
Last Modified: 15-Mar-2016
Copyright © 2000-2010 Cummins Inc. All rights reserved.
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4/5/2016