Dodge RAM TRUCK 1500 1995 Service Manual page 1148

14 - I I GENERAL DIAGNOSIS—EICEPT DIESEL
B R
FUEL INJECTOR TEST
To perform a complete test of the fuel injectors and
their circuitry, refer to DRB scan tool and appropri­
ate Powertrain Diagnostics Procedures manual. To
test the injector only, refer to the following:
Disconnect the fuel injector wire harness connector
from the injector (Figs. 44 or 45). Place an ohmmeter
across the injector terminals. Resistance reading
should be approximately 14.5 ohms ±1.2 ohms at
20°C (68°P).
INJECTOR J9214-30
Fig. 44 Typical Fuel Injector Wiring Connector
SPACER J9414-58
Fig. 45 Fuel Injector Internal Components—Typical
FUEL P U i P PRESSURE TEST
Refer to Fuel Pump Pressure Test in the Fuel De­
livery System section of this group.
ON-BOARD DIAGNOSTICS (OBD)—GAS POWERED
VEHICLES
The powertrain control module (PCM) has been
programmed to monitor many different circuits of the
fuel injection system. If a problem is sensed in a
monitored circuit often enough to indicate an actual
problem, a diagnostic trouble code (DTC) is stored.
The DTC will be stored in the PCM memory for even­
tual display to the service technician. If the problem
is repaired or ceases to exist, the PCM cancels the
DTC after 51 engine starts.
Certain criteria must be met for a diagnostic trou­
ble code (DTC) to be entered into PCM memory. The
criteria may be a specific range of engine rpm, engine
temperature and/or input voltage to the PCM.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal­
function has occurred. This may happen because one
of the DTC criteria for the circuit has not been met.
Example: assume that one of the criteria for the
MAP sensor circuit is that the engine must be oper­
ating between 750 and 2000 rpm to be monitored for
a DTC. If the MAP sensor output circuit shorts to
ground when the engine rpm is above 2400 rpm, a 0
volt input will be seen by the PCM. A DTC will not
be entered into memory because the condition does
not occur within the specified rpm range.
A DTC indicates that the powertrain control mod­
ule (PCM) has recognized an abnormal signal in a
circuit or the system. A DTC may indicate the result
of a failure, but never identify the failed component
directly.
There are several operating conditions that the
PCM does not monitor and set a DTC for. Refer to
the following Monitored Circuits and Non-Monitored
Circuits in this section.
MONITORED CIRCUITS
The powertrain control module (PCM) can detect
certain problems in the fuel injection system.
Open or Shorted Circuit - The PCM can deter­
mine if sensor output (which is the input to PCM) is
within proper range. It also determines if the circuit
is open or shorted.
Output Device Current Flow - The PCM senses
whether the output devices are hooked up.
If there is a problem with the circuit, the PCM
senses whether the circuit is open, shorted to ground
(-), or shorted to (+) voltage.
Oxygen Sensor - The PCM can determine if the
oxygen sensor is switching between rich and lean.
This is, once the system has entered Closed Loop. Re­
fer to Open Loop/Closed Loop Modes Of Operation in
the Component Description/System Operation section
for an explanation of Closed (or Open) Loop opera­
tion.