Service Bulletin
Volvo Trucks North America
Greensboro, NC USA Trucks
Date Group No. Release Page
11.2011 200 05 01 1( 5 )
Low Power Output
Symptom Fault Tracing
Low Power Output
PV776-89036459
USA50827 English
Volvo Trucks North America Date Group No. Release Page
Service Bulletin 11.2011 200 05 01 2( 5 )
Low Power Output, Fault Tracing
Symptom fault tracing
Depending on vehicle configuration, conditions related to
low power output symptoms may be caused or influenced by
specific faults or malfunctions in other vehicle components
such as axles, engine rating, bodybuilder adaptations, etc.
In such cases, refer to the specific service information
for those components. Also, fuel saving features may
be enabled on the vehicle, which could result in low
power in certain circumstances. Refer to Function Group
210, “Driving power and fuel consumption” for specific
information about VOLVO Mass-Based Variable Torque.
Note: You must read and understand the precautions
and guidelines in Service Information, Function Group 20,
"Engine Safety Practices" before performing any suggested
procedures. If you are not properly trained and certified in
a procedure, ask your supervisor for training before you
perform it.
General Information
Note: Always use Tech Tool for fault tracing.
W0064147
Note: During fault tracing, the engine should be run at the
operating temperature as well as at the temperature where
the symptom occurs.
• Low power in combination with normal fuel consumption
may have several causes. If no external symptoms
are displayed, check the fuel, air, exhaust system,
compression, the mechanical parts of the engine and
the engine control system.
Volvo Trucks North America Date Group No. Release Page
Service Bulletin 11.2011 200 05 01 3( 5 )
Basic Conditions for Achieving the Correct Tractive Power
The following conditions should be met in order for the Air Supplied to the Engine
engine to yield the right tractive power:
A reduced amount of air supplied to the engine means that
• Access to the right amount of fuel the fuel delivery is also reduced, and this results in lower
• Access to the right amount of air power output.
• The engine should emit exhaust gases without any The supply of air to the engine may be affected by:
hindrance • A damaged or restricted air inlet
• The engine should be in a mechanically fault-free • A restricted or dirty air cleaner (ACL)
condition
• A leaking charge air pipe (joints)
• The ignition temperature is sufficiently high in the
cylinders • A leaking charge air cooler
• The engine control system, including sensors, should be • A clogged charge air cooler
free from faults • Damaged turbine wheels in the turbocharger or
Fuel turbocharger housings
If the engine is supplied with too little fuel or fuel of a poor • A restricted exhaust gas recirculation (EGR) cooler
grade, this will have a negative effect on the tractive power. (exhaust gases not adequately cooled)
Environmental diesel fuels also have a negative effect on
• Defective EGR control valves
tractive power. • Altitude
The following can negatively affect fuel injection: It is important that both the engine's air inlet and the
turbocharger are free from faults.
• Restricted or dirty fuel filter(s) or fuel/water separator
filter Never replace a turbocharger because of poor power output
without first determining that the turbocharger has damaged
• Faulty overflow valve
components.
• Worn or faulty fuel supply pump
Exhaust System, Back Pressure
• Air leakage into the fuel supply pump supply line
Restrictions on the exhaust side means that it is difficult to
• Kinks or blockage in any of the fuel lines emit exhaust gases, therefore causing the exhaust back
• Restricted vent line or valve at the fuel tank pressure to increase. This, in return, results in difficulty
getting a sufficient amount of fresh air into the cylinders to
• Impurities in the fuel efficiently burn the fuel being injected into the cylinders.
• Poor fuel grade
The direct result of this is a lower intake manifold pressure,
inferior response, and higher fuel consumption.
An incorrectly rebuilt exhaust system with a lot of bends
may mean that the engine cannot emit its exhaust gases
freely. The same problem will arise if the exhaust system
is damaged (flattened), or if the shutter in the exhaust
pressure governor (if equipped) seizes or is damaged.
Compression
The compression is a good measure of the mechanical
condition of the engine. If there is sufficient compression,
the temperature in the cylinder is probably also sufficient.
Generally speaking, low compression is noticeable when
you have starting problems that worsen as the engine gets
hot or when there is blue oil smoke or abnormal amounts of
crankcase gases. A problem may be indicated when one
cylinder's compression is significantly lower than the others.
Minor deviations between cylinders are normal.
Volvo Trucks North America Date Group No. Release Page
Service Bulletin 11.2011 200 05 01 4( 5 )
Engine Control System
The engine control system, including sensors, should be
free from faults.
Note: When there are faults on some components, such as
the intake manifold pressure sensor, the result is a natural
reduction of the tractive power.
Evaluation
If none of these areas shows abnormal values, yet the
customer still maintains that the vehicle still has low power,
a reliable dynamometer test should be carried out.
If this test does not show that the vehicle has low power, no
further technical measures should be taken. Go through
the results together with the customer.
The customer's complaints could be related to the vehicle's
specification, or that the customer's references are not
comparable with the actual vehicle. If faults can not be
found on the vehicle, there could be other circumstances
that make the customer dissatisfied, i.e. his experience of
noise from the vehicle may have changed. Also, fuel saving
features may be enabled on the vehicle, which could result
in low power in certain circumstances.
If the dynamometer test shows that the vehicle clearly
has low power, fault tracing should continue in order to
determine in which system the fault may be.
Fault Tracing
Temporary faults can be difficult to trace since the fault may
not occur when the vehicle is brought in to be checked.
Fault tracing should be performed based on what the
driver has experienced. The information that the driver
has provided in conjunction with the gathering of factual
data should form the basis of how the problem should be
resolved.
Whenever possible, try to recreate the problem in an
environment and situation similar to the one described by
the driver.
Begin by determining if anything has recently happened
to the vehicle that could point to the electrical system, but
which does not have anything to do with the engine control
system.
Volvo Trucks North America Date Group No. Release Page
Service Bulletin 11.2011 200 05 01 5( 5 )
Sudden Loss of Power
Sudden power loss may be caused by:
• Failure in a component or system causing a lack of fuel
or air, or intake/exhaust restrictions.
• Poor fuel quality.
• Mechanical problems in internal engine components.
• Factors monitored by the engine control system,
including sensor faults, high coolant temperature or high
engine load.
• Exhaust gas recirculation (EGR) valve faults.
• Turbocharger malfunction.
Gradual Loss of Power
Gradual power loss may be caused by:
• Gradual failure in a component or system causing
irregular combustion.
• Air intake restrictions.
• Exhaust restrictions.
• Exhaust gas recirculation (EGR) valve faults.
Engine Does Not Reach Rated Speed
Difficulty reaching rated engine speed may be caused by:
• Problems in the fuel or intake system.
• Specific diagnostic trouble fault codes (DTC) generating
a response by the engine control system.
Low Power After Vehicle Repair
In case of sudden low power after a vehicle is repaired
or rebuilt, it should be determined whether the cause is
related to an engine component or a fault in another vehicle
component. Low power can also be caused by:
• Incorrect (unauthorized) or improperly installed engine
components.
• Engine control module (ECM) limiting engine speed
or torque because of a diagnostic trouble code (DTC)
generated by faulty or improperly installed electrical
components.
