Volvo Symptom D12D US02 Service Manual page 94

Group 20
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.
Engine Brake Does Not Function
In most cases, a non-functioning engine brake may be
caused by problems with systems that are prerequisites
for engine brake function, such as vehicle speed and
engine oil temperature. In addition, mechanical or
electrical problems in components, especially EPG-
or VCB-related components, may affect engine brake
function.
The following checks should be performed in order until
the fault is found. These checks also can help exclude
components with no faults or malfunctions. The amount
and sequence of checks depend on results from Basic
Checks (including active or inactive fault codes noted),
Poor Engine Brake Performance
Engine brake performance is affected primarily by engine
friction, the EPG brake, and the VCB brake. Faults in
these components may decrease engine braking.
An engine brake "cutting off" at higher speeds may be
caused by excessive charge pressure (possibly due to
low air pressure to the EPG); if the engine control system
senses abnormally high charging pressure, it will not
enable the engine braking function).
The following checks should be performed in order until
the fault is found. These checks also can help exclude
components with no faults or malfunctions. The amount
and sequence of checks depend on results from Basic
Step 1: Fault Code Readings
90
C2002639
D
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.
For specific symptoms, see:
•
"Engine Brake Does Not Function" page 90
•
"Poor Engine Brake Performance" page 90
"Engine Brake Complaints" page 89
vehicle conditions, vehicle service and repair history,
other symptoms, and information from the driver.
•
"Step 1: Fault Code Readings" page 90
•
"Step 2: Visual Inspection (System Checks)" page 91
•
"Step 3: VCADS Pro Tests" page 91
•
"Step 4: Component and Function Checks" page 93
"Engine Brake Complaints" page 89
Checks (including active or inactive fault codes noted),
vehicle conditions, vehicle service and repair history,
other symptoms, and information from the driver.
•
"Step 1: Fault Code Readings" page 94
•
"Step 2: Visual Inspection (System Checks)" page 94
•
"Step 3: VCADS Pro Tests" page 95
•
"Step 4: Component and Function Checks" page 96
"Engine Brake Complaints" page 89
Active and inactive registered fault codes can point to
faults but also be a fault finding aid for the symptom.
Freeze frames of information for specific fault codes may
also be helpful for finding causes for the symptom.
Fault tracing using relevant service information
should always be carried out for relevant fault codes.
Components/functions of special interest:
•
MID 128, Engine ECU
PID 84 Vehicle speed
PID 91 Accelerator pedal
PID 102 Intake manifold pressure
PID 153 Crankcase pressure
PID 175 Engine oil temperature
PPID 122 Compression brake, VCB