Ford Explorer: General Information / Description and Operation - Diagnostic Methods
This
document provides critical diagnostic knowledge required for successful
repair outcomes. It identifies technical competencies expected by users
of this manual.
Ford Diagnostic Assumptions
Ford
diagnostics assume the vehicle concern described by the test title is
currently present. Exceptions to this rule are noted in each test. Do
not replace modules or other components as directed by a diagnostic if
the concern is not present at the time of testing.
The Use of Flex Probes and Checking Wiring Pin (or Terminal) Fit
-
To avoid wiring pin (terminal) damage, Rotunda Flex
Probes (NUD105-R025F or Terminal Probe Kit 418-S035) must be used to
connect test equipment or jumper wires to pins.
-
Male to female pin (terminal) fit is critical for a consistent and strong electrical connection.
-
Pin fit may be checked by using the mating pin to
test for normal separation force. A damaged pin will have very low
separation force from the mating pin.
-
Correctly checking the separation force of small
pins may require removal from the connector hardshell (pin guide or
retainer) if it adds drag to the pin insertion or removal.
-
Replace damaged connectors, pins, or terminals.
Measuring Automotive Circuits
Checking Power-Providing Circuits
Measuring
a power providing circuit for voltage with the intended load
disconnected will only identify open circuits (for example, an open fuse
or circuit). This measurement practice will not identify excessive circuit resistance.
-
Circuits carrying approximately 200-1000 mA may be
loaded with a 250-350 mA test light. Measure circuit voltage with a DMM
while the test light is connected. A reduction in the voltage present
during test-light-loading indicates excessive circuit resistance.
-
Conductor sizes 24 gauge (0.5 mm) or smaller are
generally used to carry approximately 1000 mA (1 ampere) or less. Use
of a 250-350 mA test light to load these circuits is appropriate.
-
Circuits carrying more than one ampere should be
loaded with a device requiring similar current (for example, a brake
light bulb). A reduction in the voltage present during loading indicates
excessive resistance.
-
Conductor sizes 20 gauge (0.8 mm) or larger are generally used to carry 1 ampere (1000 mA) or more.
-
Using a voltage-drop measurement is best practice and more accurate for higher current circuits.
Checking Ground-Providing Circuits
The
best method of checking ground circuits is to measure the circuit
voltage drop during component operation (or attempted operation).
-
An ohmmeter may be accurately used if the battery has been disconnected.
-
Expect less than 2 ohms for most small diameter (18 gauge and smaller) wires.
-
Disconnecting the battery is critical because DMM
ohmmeter readings are commonly corrupted by the normal voltage present
(battery connected) across body and chassis ground circuits.
Checking Circuit Resistance or Continuity
-
Expect less than 2 ohms of resistance for most wiring harness circuits.
-
A standard DMM
ohmmeter’s low-resistance resolution (approximately 0.1 ohm) limits its
accurate use to circuits carrying less than approximately 5 amperes.
This is because very small resistances, undetectable by a standard DMM,
cause significant voltage and power loss in higher current circuits.
-
A voltage drop measurement is required for higher current circuits.
-
Standard DMM
apply a small amount of voltage to the circuit or component to
calculate resistance. As a result, these ohmmeters are very sensitive to
any level of voltage present. Voltage present in the circuit will
corrupt the DMM reading.
-
Recommended practice: Reverse the leads and
check for changes in the resistance measurement. Reversing the DMM lead connections should never change the resistance measurement (unless the circuit contains a semi-conductor). Measurement differences when leads are interchanged at the test points indicate invalid test results.
Checking For Unintended Continuity (Shorts) To Other Circuits
A DMM may be used to detect undesired circuit connections to:
-
Ground
-
Recommended practice: Disconnect both ends of
the circuit. Measure the resistance between the suspect circuit and
ground. Expect resistance greater than 10,000 ohms.
-
Other unpowered circuits
-
Recommended practice: Disconnect both ends of
the two circuits. Using an ohmmeter measure between the two circuits.
Expect resistance greater than 10,000 ohms.
-
Powered circuits
-
Recommended practice: Disconnect both ends of
the circuit. Turn on ignition/run power (key on). Using a voltmeter,
measure the voltage between the suspect circuit and ground. Expect no
voltage.
Checking Circuits by Back-Probing a Connector
Back-probing
should only be employed where a diagnostic step requires a circuit to
be tested under actual operating conditions. Back-probing is a risky
testing method due to the uncertainty of the probe connection and the
possibility of damaging terminals
-
Back-probing may be used where a circuit must be
analyzed with the voltage-drop method. All voltage-drop tests will
measure a small amount of voltage (expect less than 5 percent of circuit
operating voltage).
-
A zero-volt result indicates incorrect test conditions (no current flow or bad back-probe connections).
-
Occasionally, module failure mode behavior will
change the operation of a circuit when it is opened for testing.
Back-probing allows testing without altering normal module function.
Back-probing may be employed for circuit analysis if the following cautions are carefully observed:
-
Do not force test leads or other probes into
connectors. Adequate care must be exercised to avoid connector terminal
damage while ensuring good electrical contact is made with the circuit
or terminal. Failure to follow these instructions may cause damage to
wiring, terminals, or connectors, and subsequent electrical faults.
-
Use back probes specifically designed for the
purpose to assist in making a good test connection and to prevent
connector or terminal damage during back-probing.
-
Back-probing is the wrong test for a single point
test for presence of voltage. When zero volts is a possible result, you
cannot tell the difference between a bad probe contact and a zero-volt
result. Disconnect the circuit and test normally.
-
Back-probing is the wrong test for circuit
continuity or opens (using an ohmmeter) between two points. You cannot
tell the difference between bad probe contacts and an open circuit.
Disconnect and isolate the circuit, and test normally.
Circuit Analysis Using Jumper Wires (Creating Substitute Circuits)
Jumper wires may be employed for circuit analysis if the following cautions are carefully observed:
-
Always use fused jumper wires — the recommended
universal-testing jumper wire fuse is 5 amperes or less; larger fuse
ratings should be used only when the load requires them.
-
Use flex probes or equivalent to prevent connector terminal damage.
-
Flex probes are not intended to carry high
current (greater than 5 amperes). Do not use them to connect power for
cooling fans, blower motors, or other high current devices.
-
Follow diagnostic test directions carefully when
using jumper wires to avoid component or harness damage caused by
incorrect jumper connections.
-
Never repair a circuit by adding a new wire in
parallel to the old one (overlaying the circuit) without fully
understanding what caused the circuit to fail. Always find, examine, and
repair the fault to correct the root cause and to repair any adjacent
wiring that has been damaged.
Making Voltage-drop Measurements
A
voltage-drop test measures the loss of power or voltage in a circuit.
Losses can be measured on the ground or power (negative or positive)
circuits of any device.
-
Measuring voltage-drop requires
-
A voltmeter connected at the beginning and end of the suspect circuit.
-
An operating, or attempting to operate, circuit. Power must be on and available to flow.
-
The polarity of the voltmeter lead connections should follow conventional current flow.
-
A zero-volt reading indicates bad voltmeter connections or the component has not been turned on.
-
A small amount of voltage indicates normal circuit
loss. In 12-volt circuits, this is usually less than 0.5 volts (expect
less than 5 percent of circuit operating voltage).
-
Voltage indications greater than 0.5 volts
indicate abnormal voltage loss. Abnormally high voltage drop indicates
bad wires or connectors are causing high circuit resistance.
Using Module PID
Electronic
modules connected to a network usually offer diagnostic scan tool
measuring of internal data or operating values. This data is known as a
parameter ID or PID.
-
Using a diagnostic scan tool, PID input values, output states, and diagnostic states may be read.
-
Monitoring PID
information in the datalogger function of the diagnostic scan tool
allows detailed, accurate testing without vehicle disassembly and
cumbersome equipment.
-
Datalogger displays are the “behind the scenes” information for almost every function on a modern vehicle.
-
Controlling most module outputs with a PID is possible. For example, an output state command PID for a cooling fan, engine RPM, and many other module outputs are commonly available.
Checking Modules
Unnecessary replacement of a module is the result of improper or inadequate testing.
-
Understand correct module function. Read Description and Operation for the system.
-
Make sure programmable parameters are set correctly for
the function in question (Refer to 418-01 Module Configuration for more
information).
-
Resolve DTC first — as directed by workshop manual diagnostics.
-
Test all inputs, both hard-wired and networked.
-
Test outputs (see "Checking module switching circuits" below).
-
Check for module software updates (flash programming).
Checking Module Switching Circuits
-
Using the diagnostic scan tool module Output State
Control function to activate components is a fast way to confirm an
output is capable of being switched on and off by the module. Testing
that reveals normal module output function confirms the need to analyze
the module inputs.
-
Do not apply ground or power directly to module
switched components with jumper wires unless directed by a workshop
manual procedure, as the component could be damaged by a direct
connection to ground or power.
WARNING:
Air conditioning liquid refrigerant R-134a and R-1234yf are
capable of harming eyes or freezing skin. Always wear safety goggles and
avoid contact with liquid refrigerant...
WARNING:
Before working on or disconnecting any of the fuel tubes or fuel
system components, relieve the fuel system pressure to prevent
accidental spraying of fuel...
Other information:
Symptom Chart(s)
Symptom Chart: Brake System
Diagnostics in this manual assume a certain skill level and knowledge of Ford-specific diagnostic practices. REFER to: Diagnostic Methods (100-00 General Information, Description and Operation).
Condition
Possible Sources
Actions
The red brake warning indicator and the yellow ABS warning indicator a..
Special Tool(s) /
General Equipment
Interior Trim Remover
Removal
NOTE:
Removal steps in this procedure may contain installation details.
Open the rear tail gate.
Release the clips and remove the upper liftgate trim panel...