length DODGE RAM 2001 Service Repair Manual

tional to the amount of oxygen in the exhaust. The
information obtained by the sensor is used to calcu-
late the fuel injector pulse width. This maintains a
14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio,
the catalyst works best to remove hydrocarbons (HC),
carbon monoxide (CO) and nitrogen oxide (NOx) from
the exhaust.
The O2S is also the main sensing element for the
Catalyst and Fuel Monitors.
The O2S can fail in any or all of the following
manners:
²slow response rate
²reduced output voltage
²dynamic shift
²shorted or open circuits
Response rate is the time required for the sensor to
switch from lean to rich once it is exposed to a richer
than optimum A/F mixture or vice versa. As the sen-
sor starts malfunctioning, it could take longer to
detect the changes in the oxygen content of the
exhaust gas.
The output voltage of the O2S ranges from 0 to 1
volt. A good sensor can easily generate any output
voltage in this range as it is exposed to different con-
centrations of oxygen. To detect a shift in the A/F
mixture (lean or rich), the output voltage has to
change beyond a threshold value. A malfunctioning
sensor could have difficulty changing beyond the
threshold value.
OXYGEN SENSOR HEATER MONITOR
If there is an oxygen sensor (O2S) shorted to volt-
age DTC, as well as a O2S heater DTC, the O2S
fault MUST be repaired first. Before checking the
O2S fault, verify that the heater circuit is operating
correctly.
Effective control of exhaust emissions is achieved
by an oxygen feedback system. The most important
element of the feedback system is the O2S. The O2S
is located in the exhaust path. Once it reaches oper-
ating temperature 300É to 350ÉC (572 É to 662ÉF), the
sensor generates a voltage that is inversely propor-
tional to the amount of oxygen in the exhaust. The
information obtained by the sensor is used to calcu-
late the fuel injector pulse width. This maintains a
14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio,
the catalyst works best to remove hydrocarbons (HC),
carbon monoxide (CO) and nitrogen oxide (NOx) from
the exhaust.
The voltage readings taken from the O2S sensor
are very temperature sensitive. The readings are not
accurate below 300ÉC. Heating of the O2S sensor is
done to allow the engine controller to shift to closed
loop control as soon as possible. The heating element
used to heat the O2S sensor must be tested to ensure
that it is heating the sensor properly.The O2S sensor circuit is monitored for a drop in
voltage. The sensor output is used to test the heater
by isolating the effect of the heater element on the
O2S sensor output voltage from the other effects.
LEAK DETECTION PUMP MONITOR (IF EQUIPPED)
The leak detection assembly incorporates two pri-
mary functions: it must detect a leak in the evapora-
tive system and seal the evaporative system so the
leak detection test can be run.
The primary components within the assembly are:
A three port solenoid that activates both of the func-
tions listed above; a pump which contains a switch,
two check valves and a spring/diaphragm, a canister
vent valve (CVV) seal which contains a spring loaded
vent seal valve.
Immediately after a cold start, between predeter-
mined temperature thresholds limits, the three port
solenoid is briefly energized. This initializes the
pump by drawing air into the pump cavity and also
closes the vent seal. During non test conditions the
vent seal is held open by the pump diaphragm
assembly which pushes it open at the full travel posi-
tion. The vent seal will remain closed while the
pump is cycling due to the reed switch triggering of
the three port solenoid that prevents the diaphragm
assembly from reaching full travel. After the brief
initialization period, the solenoid is de-energized
allowing atmospheric pressure to enter the pump
cavity, thus permitting the spring to drive the dia-
phragm which forces air out of the pump cavity and
into the vent system. When the solenoid is energized
and de energized, the cycle is repeated creating flow
in typical diaphragm pump fashion. The pump is con-
trolled in 2 modes:
Pump Mode: The pump is cycled at a fixed rate to
achieve a rapid pressure build in order to shorten the
overall test length.
Test Mode: The solenoid is energized with a fixed
duration pulse. Subsequent fixed pulses occur when
the diaphragm reaches the Switch closure point.
The spring in the pump is set so that the system
will achieve an equalized pressure of about 7.5º H20.
The cycle rate of pump strokes is quite rapid as the
system begins to pump up to this pressure. As the
pressure increases, the cycle rate starts to drop off. If
there is no leak in the system, the pump would even-
tually stop pumping at the equalized pressure. If
there is a leak, it will continue to pump at a rate rep-
resentative of the flow characteristic of the size of the
leak. From this information we can determine if the
leak is larger than the required detection limit (cur-
rently set at .040º orifice by CARB). If a leak is
revealed during the leak test portion of the test, the
test is terminated at the end of the test mode and no
further system checks will be performed.
25 - 16 EMISSIONS CONTROLBR/BE
EMISSIONS CONTROL (Continued)

Items found requiring adjustment and/or repair
should be corrected before delivery of the vehicle.
NOTE: It is the dealer's responsibility to protect
new vehicles from damage and deterioration prior
to retail delivery both before and after new vehicle
preparation.
The information includes the following features:
Inspection points are cross-referenced to the New
Vehicle Preparation Form as follows:
²Titles indicate the general area being inspected
or the types of checks being made (i.e., underhood,
body-exterior, road test, etc.).
²Sub-Titles identify the types of items to be
inspected in that area (i.e., lines/hoses, wiring, etc.).
Procedures follow a logical order to prevent dupli-
cation and wasted effort.
Tips to help you do a better job are found as
NOTES.
RECEIVING
INSPECTION
The following procedures are recommended for
your own protection upon receipt of new vehicles.
When a new car is delivered by the carrier, it should
be inspected to ensure that it is in good condition
and to determine if there is any shortage or transpor-
tation damage.
EXTERIOR
Upon receipt of a new vehicle, check immediately
for:
²Under carriage damage
²Chipped or cracked windshield, broken windows,
and loose or missing moldings and name-plates
²Dents, scrapes, scratches, chips, dirt in paints or
other damage to the body exterior
²Damaged or missing side view mirror(s)
²Missing wheel nuts
²Broken or missing lenses
²Chafing, bruises, cuts, or scrapes on tire side-
walls or tread
²Missing underhood items
²Missing fuel filler cap
²Shipped loose items-license plate bracket, spare
tire, jack and tire wrench, radio antenna, floor mats,
wheel covers, cargo nets, fuses and other items²Ensure that IOD fuse is removed
²Check battery test indicator when easily visible,
or use voltmeter (battery must be at 12.4 volts or
greater). Charge to ensure green dot-visibility, per-
manent damage may occur if battery remains in a
discharged state for any length of time.
INTERIOR
Check interior items such as:
²Rearview mirror
²Accessory control knobs
²Smokers package items
²Keys
²Radio
²Special equipment items listed on shipper
²Owner's Manual and Consumer information Bro-
chures (normally stored in the glove box).
²Cuts, abrasions or stains on interior trim.
NOTE: Remember a careful look at new vehicles
when they are received may prevent problems when
preparing vehicles for delivery to your customers.
MAJOR INSPECTION POINTS
(1) Check operation of hood latch and safety catch-
adjust as required.
(2) Check all fluids for proper level and top off
with the proper fluid as required-engine oil, auto-
matic transmission fluid, brake master cylinder,
clutch master cylinder, power steering, windshield
washer, and cooling system. (Vehicle must be at nor-
mal operating temperature for some of these checks.)
(3) Check brake, clutch, fuel, and power steering
lines and hoses for leaks and clearance from moving
and hot objects-reroute to the proper location and
tighten as required.
(4) Check battery state of charge-recharge if neces-
sary, to ensure green dot is visible or instrument
panel voltmeter indicates 12.4 volts or greater.
(5) Check routing and connections of underhood
wiring, vacuum hoses, refrigerant lines and coolant
hoses for leaks, loose connections and clearance from
moving objects reroute and tighten connections as
required. Install IOD fuse on applicable vehicles.
NOTE: Reset radio, clock, compass, etc., after
installing, if vehicle is being delivered.
BR/BENEW VEHICLE PREPARATION 30 - 3
INTRODUCTION (Continued)