TSB110181-052420

Engine Speed Instability Related to Truck Vacuum Blower or Pump Engagement
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Technical Service Bulletin
Technical Service Bulletin:
Released Date: 24-May-2019
TSB110181
Engine Speed Instability Related to Truck Vacuum Blower or Pump
Engagement
Engine Speed Instability Related to Truck
Vacuum Blower or Pump Engagement
Core 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.
Confirmation
Product Affected:
•
•
•
•
•
•
•
ISL9 CM2350 L101
ISX15 CM2250
ISX15 CM2250 SN
ISX15 CM2350 X101
ISX12 CM2350 X102
ISX12/ISX11.9 CM2250
X12 CM2350 X119B
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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5/29/2019
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.
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Document History
Date
Details
2011-6-14
Module Created
2011-12-21
Updated Information.
2012-2-27
Updated Information.
2014-9-29
Additional engines added.
2015-4-22
Additional engines added.
2016-3-14
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.
2019-5-24
Added X12 CM2350 X119B
Last Modified: 24-May-2019
https://quickserve.cummins.com/qs3/pubsys2/xml/en/tsb/2011/tsb110181.html
5/29/2019