Normal Driving Modes
Engine idle, warm-up, acceleration, deceleration
and wide open throttle modes are controlled based on
all of the sensor inputs to the ECM. The ECM uses
these sensor inputs to adjust fuel quantity and fuel
injector timing.
Limp-In Mode
If there is a fault detected with the accelerator
pedal position sensor, the ECM will set the engine
speed at 1100 RPM.
Overspeed Detection Mode
If the ECM detects engine RPM that exceeds 5200
RPM, the ECM will set a DTC in memory and illu-
minate the MIL until the DTC is cleared.
After-Run Mode
The ECM transfers RAM information to ROM and
performs an Input/Output state check.
MONITORED CIRCUITS
The ECM is able to monitor and identify most
driveability related trouble conditions. Some circuits
are directly monitored through ECM feedback cir-
cuitry. In addition, the ECM monitors the voltage
state of some circuits and compares those states with
expected values. Other systems are monitored indi-
rectly when the ECM conducts a rationality test to
identify problems. Although most subsytems of the
engine control module are either directly or indirectly
monitored, there may be occasions when diagnostic
trouble codes are not immediately identified. For a
trouble code to set, a specific set of conditions must
occur and unless these conditions occur, a DTC will
not set.
DIAGNOSTIC TROUBLE CODES
Each diagnostic trouble code (DTC) is diagnosed by
following a specific procedure. The diagnostic test
procedure contains step-by-step instruction for deter-
mining the cause of the DTC as well as no trouble
code problems. Refer to the appropriate Diesel Pow-
ertrain Diagnostic Manual for more information.
HARD CODE
A DTC that comes back within one cycle of the
ignition key is a hard code. This means that the
problem is current every time the ECM/SKIM checks
that circuit or function. Procedures in this manual
verify if the DTC is a hard code at the beginning of
each test. When the fault is not a hard code, an
intermittent test must be performed. NOTE: If the
DRBIIIt displays faults for multiple components (i.e.
ECT, VSS, IAT sensors) identify and check the
shared circuits for possible problems before continu-
ing (i.e. sensor grounds or 5-volt supply circuits).
Refer to the appropriate schematic to identify shared
circuits. Refer to the appropriate Diesel Powertrain
Diagnostic Manual for more information.
INTERMITTENT CODE
A DTC that is not current every time the ECM/
SKIM checks the circuit or function is an intermit-
tent code. Most intermittent DTCs are caused by
wiring or connector problems. Problems that come
and go like this are the most difficult to diagnose;
they must be looked for under specific conditions that
cause them. NOTE: Electromagnetic (radio)
interference can cause an intermittent system
malfunction. This interference can interrupt com-
munication between the ignition key transponder and
the SKIM. The following checks may assist you in
identifying a possible intermittent problem:
• Visually inspect the related wire harness connec-
tors. Look for broken, bent, pushed out or corroded
terminals.
• Visually inspect the related wire harness. Look
for chafed, pierced or partially broken wire.
• Refer to hotlines or technical service bulletins
that may apply. Refer to the appropriate Diesel Pow-
ertrain Diagnostic Manual for more information.
ECM DIAGNOSTIC TROUBLE CODES
IMPORTANT NOTE: Before replacing the ECM for
a failed driver, control circuit or ground circuit, be
sure to check the related component/circuit integrity
for failures not detected due to a double fault in the
circuit. Most ECM driver/control circuit failures are
caused by internal failures to components (i.e. relays
and solenoids) and shorted circuits (i.e. sensor pull-
ups, drivers and ground circuits). These faults are
difficult to detect when a double fault has occurred
and only one DTC has set. If the DRBIIIt displays
faults for multiple components (i.e.VSS, ECT, Batt
Temp, etc.) identify and check the shared circuits for
possible problems before continuing (i.e. sensor
grounds or 5-volt supply circuits). Refer to the appro-
priate wiring diagrams to identify shared circuits.
Refer to the appropriate Diesel Powertrain Diagnos-
tic Manual for more information.
8Ea - 2 ELECTRONIC CONTROL MODULES WG
ENGINE CONTROL MODULE (Continued)
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