A6 - "Diagnostic Tools" How, Codes, Measurements

DMMS, Test-light, Voltmeter. Ammeter, Ohmmeter, Jumper wires, Scan tool, Oscillopes

Why is voltage also called potential difference?

Changes throughout the circuit when experiencing loads, resistors, ect.

What Are Oscillopes?

Graph Electrical Signals (Voltage) overtime

Define DSOs (Digital Storage Oscillopes)

Store and reconstruct signal samples for analysis

What is a LASs (Live Analog Scopes)

Require a repetitive signal to display real-time voltage changes / voltage signals.

What can Oscillopes diagnose?

Intermittent issues that a standard Voltmeter cannot detect; Compare waveforms to ‘known good‘ waveforms for diagnostics

What is a jumper wire?

they are a crocodile end wires used to located open circuits on the power or ground side.

What Jump-Wire Should I always use?

Fuse protected jump wires.

Safety Advisery in tight spacees for jump-wires?

Backprobe pins, insulated boots.

What is a Voltmeter?

Measures voltage in a certain-point in a circuit. And/or Dropped Voltage; it isn’t sensitive to polarity(so can be connected in either way)

What can a voltmeter diagnose?

can diagnose too much dropped voltage to find out the (stealer) stealing all the current from unwanted resistance; Also can measure enough voltage passing through entirely circuit comparing points.

What is a test light?

Old-Diagnostic tool used to diagnose if a circuit is complete the test light turns on if the voltage is going through it.

How to use a test light?

Positive lead on (positive terminal, or component), Negative lead on (Ground, negative, terminal)

Advisory against test lights?

Test lights should only be used if the manufacturer manual tells you to do so; other than that don’t test lights can damage new car models that use computer controlled systems.

use a Voltmeter as a Parrelel and/or Series?

Connect only in parallel;

How to measure voltage in a Voltmeter?

First get type of current(AC / DC) then start with a higher volt range and lower slowly to get a precise reading on the voltage.

First step to Electrical Diagnosis?

Measure voltage on batter; if the battery 12.6 volt or higher its well charged, if the battery is 11.5 or less its not charged and its a SOC(low state-of-charge)

AC vs DC

AC -Alternating Current; Current flow can go multiple ways. (Common in alternators to recharge the battery)

DC - Direct Current; current flow go only one way (Almost everything powered by energy in a vehicle is DC besides a alternator)

How to connect a Voltmeter?

!Connect the probes! DC

Black probe to negative terminal / ground

Red probe to circuit or device or component

What does Ohmmeter diagnose?

Excessive Resistance & low-resistance

How to use a ohmmeter

An ohmmeter can be used to perform continuity tests for opens or shorts and to read actual resistance in a non-live (dead) circuit

Measurements of a ohmmeter

Usually the selector switch allows the multiplication of the meter reading by either 10, 100, 1000, etc. or 2, 20, 200, 2000, etc. Since all ohmmeters are powered by an internal battery (usually a 9 volt), the ohmmeter can be used as a continuity test in non-live circuits

Polarity of a Ohmmeter?

Since the ohmmeter uses its own voltage source, either lead can be connected to any test point. In using the meter for making continuity checks

Outside current affects Ohmmeter?

Current flow from an outside voltage source, such as a vehicle battery, can damage an ohmmeter. The circuit or component should be isolated from the vehicle electrical system before any testing is done. 

Reading a Ohmmeter?

Zero resistance, or any resistance readings, indicates continuity in the circuit. Infinite resistance indicates an open in the circuit. A high resistance reading where there should be none indicates a problem in the circuit.

What is Ohmmeter also known as?

A static test; voltage drop tests are preferred because when current goes through one pathway it may not be strong enough to handle the load and will fail. Reason being volt drop tests are recommended

Oscillope & Voltmeter is a series or Parrelel and are there polarity sensitive?

Voltmeter is Parralel and is polarity sensitive, Oscillope is sensitive to polarity and is parralel

What is Ohmmeter Polarity & Parralel or Series?

Ohmmeter isn’t sensitive to polarity and can be connected in both series & parralel

1st step before using Ohmmeter?

De-energize the circuit: Always ensure the circuit you are measuring is completely de-energized (no power source connected) before using an ohmmeter. Measuring resistance in a live circuit can damage the meter and potentially cause a shock. 

Ammeter can diagnose what?

It can diagnose By referring to a specific current draw rating, measuring the amperes and comparing the two values, one can determine what is happening within the circuit to aid in diagnosis. For example, an open circuit will not allow any current to flow, so the ammeter will read zero. More current flows through a heavily loaded circuit, or when the supply voltage is increased, such as when the charging system is operating; it will measure current draw only when the circuit is closed and electricity is flowing.

Is Ammeter polarity sensitive & is it Parralel or Series?

It is sensitive to polarity and is always connected in series

Sensitive vs Non-Sensitive Polarity Tools?

"Polarity-sensitive" means a device or component functions correctly only when the positive (+) and negative (-) terminals are connected in the correct orientation, and reversing the polarity can cause it to malfunction or fail. 

"Non Polar-sensitive" means a device or component functions correctly in both ways (+) and negative (-) terminals are connected in Either orientation, and reversing the polarity can cause no damage to the circuit and tool. 

Series vs Parrelel Diagnostic Tools?

Series diagnostics tools typically perform tests in a specific order, one after another. 

Parallel diagnostics tools allow for testing and measuring multiple systems or components at the same time.

BACKPROBING/PIERCING

Backprobing involves carefully sliding a thin stiff wire or long pin into the back side of the connector to make electrical contact. Use caution when inserting pins into the back side of connectors to avoid damaging them or the wire insulation. Be sure to seal any piercing with liquid electrical tape or even clear fingernail polish to prevent moisture from entering the wiring, and causing corrosion to form. NEVER USE SILICONE AS A SEALING AGENT.

This allows to check for current through a connector this is just a important method to diagnosing

What are jumper wires

Jumper wires are used to bypass sections of a circuit. The simplest jumper wire is a length of multi-strand wire with alligator clips or appropriate spade or pin connectors at each end,Always use a fuse protected jumper wire to prevent accidental damage to the vehicle’s wiring harness. 

What does jumper wires diagnose & how to set up

Jumper wires are used primarily to locate open electrical circuits on either the ground (–) side of the circuit or on the power (+) side. If an electrical component fails to operate, connect the jumper wire between the component and a good ground.

Scope Display(Oscillope) Concept

The scope display represents values of voltage (or current) on a vertical (Y axis) scale, and values of time on a horizontal (X axis) scale. Lines (graticule) on the screen indicate divisions of values, as determined by the selected scope settings. The lower left-hand corner may represent a zero value, or a negative value, depending on the setup or configuration. The values of the vertical divisions are selectable using switches or software and are sometimes expressed as the value of the entire scale, such as a total value of 25 volts from the zero line up to the top of the scale. Other choices might include .1, .5, 1.0, 5, 10, 15 volts, etc. per “graticule” or division, with a number of horizontal and vertical divisions shown on the screen. 

Much like setting up a multimeter, begin with a value higher than expected, and work your way lower until the waveform occupies an area of the screen that lets you see the desired portion. The horizontal line values of time are also manually selected

Define KAM(Keep-Alive Memory)

Stores learned vehicle data & settings even when the power is lost.

Define PID (Parameter identification)

Live data values read from vehicle sensors

Define DLC (Data link connector)

The plug-in port for Scan tools, usually under the dashboard

Define DTC (Diagnostic Trouble Code)

A Numerical Code indicating vehicle issues

Define OBD-II (on board Diagnostic II)

The standard vehicle diagnostic system

Define Amp Clamp (inductive clamp meter)

measures current without breaking the circuit; The clamp surrounds a wire or cable carrying the current, allowing for current measurement without breaking the circuit. Detects the magnetic field generated by the current flowing through the conductor. 

Define Snapshot Data

A recording of the vehicle system conditions at the time of a fault

Define Bi-Directional Scan tool

a Scan tool capable of activating components for testing

Define PCM (Power train control module) reflash

Updating or reprogramming the vehicles control module software

Define TPS (Throttle position Sensor)

DMM vs DSO

common issue in a tip-in hesitation is an intermittent loss of signal from the Throttle Position Sensor (TPS). You can’t see it on the DMM because the problem occurs too fast for the tool to catch. But on a scope, the loss will be immediately seen as you trace the sensor signal on your screen while opening and closing the throttle.

DSO “good patterns“ what are they?

Often you may need to compare the pattern on your scope with a “known good” pattern from another vehicle. You can find several sources for these patterns online.

Whats a scan tool

A scan tool is a diagnostic tool that connects to the DLC (Data Link Connector) to communicate with the vehicle’s computers. Scan tools can be used to read DTCs (Diagnostic Trouble Codes), perform tests and monitor specific system data; Scan tools show a text display of labeled values determined by the manufacturer’s control systems and the programming module used in the scan tool. The display can be reorganized, frozen, recorded and interpreted

How to use a scan tool

Make sure the ignition key is in the OFF position when connecting a scan tool cable connector to the DLC. On pre-OBD II vehicles (1995 and earlier), an adapter may have to be used. If the scan tool is not powered through the DLC, connect the power lead(s) to the cigarette lighter or battery.

The scan tool may ask you certain questions to identify the vehicle being serviced. Most scan tools have buttons or knobs with which to input information. Once the vehicle is identified, you can then select the desired diagnostic information.

what is the code definitions in OBD-II ?

OBD II trouble codes consist of one alpha character followed by four digits. The alpha character indicates the area of the vehicle where the failure occurred. This includes (B) Body, (C) Chassis, (P) Powertrain, and (U) Network. The first digit of the DTC denotes the origin of the code. Codes authored by the SAE are identified by a zero (0). These codes are known as generic DTCs since they are the same for every vehicle. Manufacturer specific codes are indicated by the number one (1). These DTCs are part of the manufacturer’s enhanced diagnostic software, and vary between vehicle brands. The second digit in the DTC identifies the system experiencing the problem, while the last two digits correspond to a specific code definition.

DTCs vs OBD-II

DTCs (Diagnostic Trouble Codes) are the specific codes generated by a vehicle's onboard diagnostics (OBD) system, while OBD-II refers to the standard for that system

Explaining Bi-Directional Scan tools & Snapshot

Most scan tools provide “snapshot” data. This allows the technician to record problems while driving the vehicle. If there is an intermittent or condition–specific problem, the technician can takes a ‘snapshot’ of the engine control system operating conditions and PIDs, capturing the various sensor readings when the malfunction occurs. The technician can then review the information back at the shop to find the cause of the problem.

Some scan tools can be used to perform tests and are known as bi-directional scan tools. The scan tool can activate various switches and actuators and then tell you whether a component is functioning properly.

Types of Short circuits

2 types a short on the ground and a short on the power; If the short is within a component, the component will not operate properly or may not operate at all.

Check the resistance of the component with an ohmmeter; if there is a short, the resistance will be less than specified

Short to power

A short to power between circuits usually results in components operating unintentionally. This can be due to worn, abused or burned wiring insulation

Short to ground

A short to ground will usually cause a fuse to blow as soon as it is installed. However, if the short is on the ground side of the load but before a ground-side switch, the fuse will not blow but the component will not turn off. A voltmeter or a circuit probe will be useful for diagnosing electrical faults. 

Short finder

A short to ground also can be detected using a compass-like device called a “short finder.” The short finder is connected between the fuse terminals (in place of the blown fuse) and will create a pulsing magnetic field in the circuit. After installing the short finder, turn on the load device. Move the short finder meter along the circuit, beginning at the fuse box. The meter needle will deflect with each magnetic current pulse. When the meter is moved past the short, the needle will stop deflecting. This area should be checked for the cause of the short.

Burned Fuse & Problem solving

When u come across a burned fuse you will need to replace it after replacing the fuse all may seem to work well but when a fuse burns its because of high current this condition can be caused by poor insulation in the wiring, or moisture entering through a worn spot.

A mysterious short may be caused by a momentary overload. This may be due to the high load of a defective motor unit as it starts up. Usually it takes a lot more current to get an electric motor moving than to keep it moving. 

A jammed unit may cause a fuse to blow. If a motor or its mechanism is jammed, the protection device will perform its job - motor protection! A conversation with the driver may tip you off to the real cause of this kind of transient condition. More than one wiper motor or door window motor frozen in place with ice has popped its protective device when the customer turns the switch on. In the case of wiper blades, the circuit breaker will likely automatically reset. 

In the event a normal blade fuse blows, or a fusible link burns out, something is faulty and needs to be corrected.

The open may be created by a defective switch, relay or wire. In order to restore the circuit, we must find and repair the open. Check the wiring diagrams carefully and trace the normal current flow. Then trace the circuit using a voltmeter