POWER TAKE-OFF (PTO)
Peterbilt Motors Company 8-9
PTO INSTALLATIONS – 389 FAMILY
Standard PTO operation is also called cab PTO. With this feature, the operator can set the engine to pre-programmed set
speed(s) and ramp the engine speed up and down with the set/resume switch. To control the PTO there are various dash
switches that we offer. Standard with every vehicle is the Cruise Control/PTO on off switch and the Set/Resume switch.
There are also several additional PTO control switches that can be used. The PTO control switch will be plumbed with air
lines that will be plugged at the firewall bulkhead. See Section 7 for PTO dash switch plumbing and firewall bulkhead
locations. With the MX engine when the PTO dash switch is engaged a pressure switch on the air lines under the dash
will send a signal to the engine to go into PTO mode. On Cummins engines, when the cruise control switch is activated
and all parameters set in the ECM for PTO mode are met, the engine will go into PTO mode. In this mode, the engine will
respond to all PTO mode parameters that have been programmed into the software. These parameters can be changed
with INSITE on all Cummins engines and DAVIE on all MX engines. There is a PTO light on the dash that should be
wired to the PTO to inform the operator when the PTO has engaged or disengaged. This should be wired to the PTO
output, not just a dash switch or PTO enable circuit. The wire can be found in the right hand rail in the area of the
transmission. The wire is labeled WHT1513 PTO Circuit.
On Allison transmissions, the PTO’s will require an electric signal. We do not currently offer an electric PTO switch for the
389 family, but there are several options available. The most common method of getting an electric signal for the PTO is
to get a factory air switch and install a pressure switch on the air line. It is recommended to provide a 12 volt signal to the
transmission control module (TCM) and have the TCM programmed to check for specific requirements such as engine
speed, gear selection, output speed etc. before engaging the PTO. If the TCM logic is bypassed and the PTO is engaged
directly it could cause damage to the PTO and the transmission. Contact your local Allison rep for more information.
