How to Teach Scan Tools and PIDs

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How to Teach Scan Tools and PIDs

• Jim Halderman
• Dayton, Ohio

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Topics to Be Discussed

• Generic compared to factory scan tools
• Normal sensor values
• How to look at scan tool data (PIDs) in a
  particular order to reduce diagnostic time.
• How to use fuel trim to diagnosis fuel delivery
  problems.

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How Do You Teach Scan Tools?

• Let them at it?
• Show the students every parameter (PID)?
• Do you show them a procedure?
• Have you plotted scan tool data?
• How can you tell quickly the range of a sensor?
• How do you spot PIDs that are out-of-range?

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Can Scan Tools Fix Vehicles?

• No
• Scan tools are diagnostic tools.
• Scan tools are used to gather information about
  the vehicle.
• The service technician actually fixes the vehicle.

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Can the Use of a Scan Tool Damage a Vehicle?

• No.
• Care should be taken during certain
  bi-directional commands, but generally, a student
  cannot do harm to a vehicle that could happen
  with other service procedures.

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Getting Started

• Where is the DLC?
• 1996 to 1997 The DLC had to be visible with the
  drivers door open and the technician in a
  kneeling position.
• 1998 and newer The DLC can be located almost
  anywhere and can be covered.
• The cover must not need tools to remove it.

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DLC Locations
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DLC Locations
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DLC Locations
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OBD II DLC Pins

• Pin number 16 is 12 volts (4 amperes max)
• Pin 4 is chassis ground
• Pin 5 is data ground (logic low)

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CAN

• Controller Area Network
• Developed by Bosch and used by Mercedes since
  1988
• Required by all vehicle manufacturers by the 2008
  model year
• CAN C is fast (500,000 bps)
• Watch for scan tools that are CAN ready

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Affordable Scan Tools

• OTC 3960 (less than 300)
• Generic and enhanced domestic

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Affordable Scan Tools

• MAC Task Master-Enhanced OBD II plus domestic OBD
  I
• Lists for 1,000 (500 with student discount or
  to schools)

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Affordable Scan Tools

• AutoEnginuity
• (www.autoenginunity.com
• PC Pocket PC or Palm based products.
• Generic 229.95 plus 99.95 to 149.95 for each
  enhanced
• AutoTap (www.autotap.com)
• Generic OBD II-179.95
• Enhanced (all three domestics) 249.95

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Ever Seen This Before?

• No safety glasses
• Scan tool is right over the airbag
• Does not have a clue what is meant by the data

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Does the Student Know What to Look for?
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What Should a Service Technician Do First?

• Verify the customers concern.
• Check for
• DTCs.

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Steps in the Diagnostic Process

• Perform a thorough visual inspection.
• Check for TSBs.
• Look carefully at scan tool data (PID or
  Parameter Identification).
• Narrow the problem to a system or a cylinder.

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What Should a Service Technician Do First?
(continued)

• Repair the problem and determine the root cause.
• Verify the repair and clear all DTCs.

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There Are 1599 OBD II DTCs
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P0304 Example
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EGR passage problem is shown.
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Remove upper plenum for EGR inspection.
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5 out of 6 are stopped up!
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P0300 Examples
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Micro-Arcing
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Do Not Clean - Replace
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V6
V8
Encoded Cap
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Note Burn Spot
2
2
1
3
3
4
Cylinders 1/4 and 1/2
1
4
6
6
5
C
5
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8
8
1
4
1
2
2
Cylinders 3/5
7
3
4
3
7
6
6
5
5
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7
5
6
8
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EGR Carbon Build up
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Top Ten DTCs

• Based on 800,000 vehicles tested in 2004
• Wisconsin Vehicle Inspection Program
• www.wivip.com

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Why Use a Scan Tool?

• This light means that the vehicle
• is exceeding 1.5 times the Federal
• test procedures standards (FTP).
• It does not necessarily mean that there is a
  driveability-related complaint.
• Is it possible to have a performance complaint
  with a stored trouble code without having an
  illuminated check engine light? YES!!

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Scan Tools Should

• Allow a choice of factory versus generic
• Retrieve codes
• View freeze frame
• View datastream
• Perform continuous and non-continuous monitoring
• Check/interpret monitor status
• Perform bi-directional testing
• Clear codes

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Scan Tools

• Generic OBD II
• Also called Global
• Gives emission-related data only with limited
  bi-directional control
• OEM is often referred to as enhanced
• Needed for most manufacturer-specific DTCs

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Scan Tool PIDs

• PID means parameter identification.
• Most students ,when asked, say they are looking
  for something that does not seem right.
• That can be time consuming.
• There are over 400 PIDs (Ford).

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Logical Approach

• Check for DTCs and pending DTCs.
• Involves presenting what data (PIDs) should be
  looked at first, second, etc.
• A logical approach includes what the values
  should be and how to interpret the readings.
• Also includes what needs to be done to determine
  whether the reading is a result of action from a
  fault somewhere else or a failed sensor.

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Generic PIDs

• A recent national average says that 85 of all
  OBD II repairs required only the use of generic
  OBD II alone!

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Generic Versus Factory Side

• Generic
• 1. Used to monitor emission related parameters,
  both
• inputs and outputs.
• 2. Has limited bi-directional testing.
• 3. Allows graphing if the scan tool is capable.
• 4. Follows EPA standards.

• Factory
• 1. Used to monitor all inputs and outputs.
• 2. Has more data.
• 3. Typically faster.
• 4. Usually adds bi-directional testing.
• 5. May or may not allow viewing of EPA standards.

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When to Use a Factory Tool?

• When there is a P1 trouble code.
• When performing any bi-directional testing.
• When performing no-code diagnostics.
• Remember, start off by using generic OBD II.

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Reflashing

• 1. Can a reflash cure a worn out component? No,
  it is meant for a way of addressing an
  engineering defect.
• 2. Most reflashes do not actually fix the
  problem, they simply broaden the task managers
  level of acceptance.
• 3. This is primarily a dealer need by statistics
  standards.
• 4. This could be a scary thing and should not be
  done unless needed.

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Monitors

• Continuous
• Monitors
• Fuel system
• Misfire
• CCM (comprehensive component monitor)

• Non-Continuous Monitors
• Oxygen sensor
• Catalyst
• EGR
• EVAP
• Secondary AIR (not used on all makes/models)
• PCV (beginning 2000 M/Y)
• Thermostat (beginning 2002 M/Y)

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Thermostat Monitor
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PCV Monitor
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AIR Monitor
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Monitor Display
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How the MIL Is Commanded On
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Generic Modes
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Generic (Global)

• Do all vehicles have this? Yes
• Does my scan tool do this type of testing? View
  a scan tool to find out.
• Where is mode six located? The generic side of
  the OBD II.
• Is it called mode 6? Nope!
• Will I be able to understand this information?
  On older scan tools and computers, the material
  is usually displayed in hexidecimal, whereas
  newer scan tools will interpret and display in
  plain English.

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Hexadecimal Numbers

• Generic OBD-II displays often use hexadecimal
  numbers.
• Instead of 10 numbers, hexadecimal uses 16
  numbers.
• The first numbers, 0 to 9, make up the first ten
  numbers.
• Capital letters are used to express numbers 10
  through 16 (A-F).
• A dollar sign is used in front of the number to
  indicate that it is hexadecimal.

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Hexadecimal Uses

• MID Monitor Identification used to be called
  TID (Test Identification).
• 01 is rich-to-lean sensor threshold.
• 02 is lean-to-rich sensor threshold.
• 03 is low sensor voltage for switch time
  calculation.
• CID Component Identification

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PID Hex Numbers

• PID 03 - Fuel system bank 1 lean
• PID 04 - Engine load
• PID 05 - ECT
• PID 06 - STFT
• PID 07 - LTFT

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J1979 Mode 06 Data
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Chrysler Drive Cycle
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Ford Drive Cycle
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GM Drive Cycle
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Drive the Freeze Frame

• One option is to simply drive the vehicle under
  the same conditions that caused the MIL.
• If the conditions are right, the test may pass,
  thereby causing the PCM to turn off the MIL.
• This is much easier than having to perform the
  drive cycle after clearing the DTC.

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CMP Retard PID
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You MUST Crack the throttle above 1000 rpm to
reset the PID!
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PID Resets
Throttle cracked
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Gear Wear!
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Gear /Pin / Washer Kit Available
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Plate spins on shaft!
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Base line for Sensor Values(Except as mentioned)

• Normal operating temperature (cooling fans cycled
  twice)
• Idle (closed throttle)
• All accessories off
• In Park or Neutral
• Closed loop

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Step 1

• Before starting the engine, connect the scan
  tool.
• This step is very important, especially if the
  driveability concern is hard starting or cold
  driveability.

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Step 1 (continued)

• Key on and look at the values for ECT (engine
  coolant temperature) and IAT (intake air
  temperature).
• Basically, the same sensor and the two
  temperatures should agree.

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ECT IAT

• The two temperatures should be the same (within 5
  degrees).
• Both should measure the ambient air temperature.
• If the two indicate different temperatures, the
  one closer to the ambient air temperature is the
  one most likely to be correct.

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ECT IAT (continued)

• The ECT sensor has a higher authority than the
  IAT and is therefore more likely to be the cause
  of a starting or cold running problem.
• The ECT is the only sensor used by the PCM when
  the ignition key is first turned from on to start.

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Step 2MAP BARO

• Another sensor to check is the MAP sensor because
  it is a high-authority sensor, especially on
  speed density controlled engines.
• The MAP reading at KOEO should be atmospheric
  pressure (about 29.50 in. Hg.), depending on
  altitude and weather conditions.
• An easier value to remember is that it should be
  about
• 4.6-4.8 volts

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MAP Sensor Authority

• The MAP sensor is a high-authority sensor on an
  engine that uses the Speed-Density method of fuel
  control.
• If the exhaust is rich, try disconnecting the MAP
  sensor.
• If the engine now runs OK, then the MAP sensor is
  skewed or giving the PCM wrong information.

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MAP Too High or Too Low

• The sensor could be skewed.
• Check the power and ground of the sensor.
• If 5-volt reference (Vref) is low, check other
  sensors that also use the reference voltage.

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Step 3IAC Counts

• After the engine starts, observe the IAC counts
  or percentage.
• The IAC is used to control idle speed by changing
  the amount of air bypassing the throttle plate
  (just like depressing or releasing the throttle
  pedal).

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IAC (continued)

• On a warm engine (cooling fans cycled twice), the
  IAC counts should be 15-25 counts or percentage.
• If the IAC commanded position is low, a vacuum
  leak (speed density engines mostly) could be
  indicated.
• The extra air decreases the vacuum and the MAP
  sensor reads this drop as an increase in load.
  The PCM adds fuel, increasing the engine speed.

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IAC Too High

• If the IAC position is higher than normal. This
  could indicate a dirty throttle plate(s) or a
  vacuum leak on a MAF engine.

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Higher IAC

• A vacuum leak on a MAF engine is actually false
  air not measured by the MAF sensor. This can
  cause the engine speed to decrease due to the
  leaner-than-normal air-fuel mixture. The mixture
  causes the PCM to increase engine speed and
  commands a higher IAC position.
• Note Some minor vacuum leaks can cause the IAC
  to drop just like on a speed density engine.

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Step 4MAF Sensor

• Look at the amount of air entering the engine.
• There should be
• 3 to 7 grams per second (g/s)
• About 1 volt (analog MAF sensor)
• About 0.5 lb. per hour
• About 13-19 kilograms per hour (kg./hr)

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Normal MAF Readings

• Use a scan tool to look at the grams per second.
• Warm the engine at idle speed with all
  accessories off. Should read 3 to 7 grams per
  second.
• GM 3800 V-6 should read 2.37 to 2.52 KHz.
• If not within this range, check for false air or
  contamination of the sensor wire.

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MAF Sensor Diagnosis

• If the MAF sensor wire were to become coated, it
  cannot measure all of the incoming air.
• A normal warm engine at idle should be 3 to 7
  grams per second.
• Rapidly depress the accelerator pedal to WOT. It
  should read over
• 100 grams per second (scan tool) or
• higher than 7 kHz (digital MAF sensor)
• 4 volts (analog MAF sensor)

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MAF and Altitude Reading

• Barometric pressure (BARO) is determined by the
  Powertrain Control Module (PCM) software at WOT.
• At high airflows, a contaminated MAF sensor will
  under estimate airflow coming into the engine,
  and therefore, the PCM determines that the
  vehicle is operating at a higher altitude.

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Visual Inspection

• Look for a very dirty filter.
• Look for a K N filter that has been over-oiled.
• Look for fuzz on the sensing wire from fibers
  coming off of the filter paper.

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Fuzzy MAF
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False Air
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Mass Air Flow (MAF)-False Air
Usually affects operation in drive may run OK if
driving in reverse.
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MAF Sensor Authority

• High-authority sensor
• If in doubt - Take it Out!
• If the MAF sensor is disconnected, the PCM
  substitutes a backup value.
• If the engine runs OK with the MAF disconnected,
  then the MAF has been supplying incorrect
  information.

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Step 5Injector Pulse-Width

• On a warm engine, the injector pulse-width should
  be
• 1.5 to 3.5 milliseconds.

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Injector Pulse-Width Too Long

• If the PW is higher than normal (higher than 3.5
  ms)
• Extra load on the engine, such as the AC is on or
  other accessory.
• Engine has a vacuum leak or some other fault,
  causing a leaner-than-normal air-fuel mixture.

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Injector Pulse-Width Too Short

• If the injector pulse width is shorter than 1.5
  ms, the
• engine could be getting fuel from some other
  source such as
• from the EVAP system
• (purge valve stuck open)
• from the fuel in the crankcase being drawn in
  through the PCV system
• from a bad fuel pressure regulator

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Step 6Checking for Fuel Control

• If the pulse-width is a concern, verify proper
  oxygen sensor operation.
• Create a vacuum leak, and pulse-width should
  increase.
• Add propane to the inlet and pulse-width should
  decrease.

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Check Action/Reaction

• Oxygen sensor voltage should increase, and
  injector pulse-width should decrease.
• Oxygen sensor voltage should decrease, and
  injector pulse width should increase.

• Add propane
• Create a vacuum leak

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Normal Pulse-Width

• At idle, at 2000 RPM in neutral, or in park, the
  pulse-width can range from 1 to 5 milliseconds,
  but is usually between 1.5 and 3.5 ms.

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Step 7 Oxygen Sensor

• Look at the oxygen sensors for proper operation.
• Upstream sensors should fluctuate higher than 800
  mv and lower than 200 mv.

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Downstream Oxygen Sensor

• The downstream oxygen sensors should be
  relatively stable and not show too much change in
  the voltage.

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False Lean Readings

• A cracked exhaust manifold can cause oxygen to be
  drawn into the exhaust upstream from the oxygen
  sensor.
• An ignition misfire can also cause a false
  low-oxygen sensor reading.
• Remember that the oxygen sensor looks at the
  oxygen in the exhaust, not the unburned fuel!

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Antifreeze Contamination

• If the engine has had a blown head gasket, be
  sure to check or replace the oxygen sensor.
• The silicates can coat the sensor.
• Dexcool and other organic acid technology (OAT)
  coolants do not cause this problem.

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Antifreeze on an O2 Sensor
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Oxygen Sensor Authority

• The O2S is a high-authority sensor when the
  engine is operating in closed loop.
• The sensor can add or subtract up to 25 from the
  base pulse width (some vehicles even more).
• If the sensor is skewed, it can create a
  driveability problem.
• If in doubt, take it out.
• If the sensor voltage is not connected, the PCM
  will go into open loop.

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Step 8Fuel Trim

• Short-term fuel trim (STFT) is used by the PCM to
  correct for exhaust readings that are slightly
  rich or slightly lean.
• STFT can add or subtract fuel quickly.
• STFT can add or subtract only a limited amount of
  fuel.

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Long Term Fuel Trim

• Long-term fuel trim (LTFT) can add or subtract
  more fuel than STFT.
• LTFT is slower than STFT.
• The purpose of LTFT is to keep STFT within plus
  or minus 10.

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LTFT and STFT Diagnosis

• I suggest students ignore STFT.
• STFT is what is happening this instant.
• LTFT gives a history of the exhaust mixture and
  is more helpful when it comes to a diagnosis.
• Add the two together to get total amount of added
  or subtracted fuel.
• LTFT 8, STFT -3, total 5.

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Fuel Trim
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LTFT Numbers

• Ignore any fuel trim numbers less than 10.

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LTFT Too High

• Look for a vacuum leak.
• Look for a cracked exhaust manifold.

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-LTFT Too High

• Check for too high fuel pressure.
• Check for a leaking fuel pressure regulator.

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Fuel Trim Example

• LTFT 12
• STFT 2
• How is the engine running now?

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Fuel Trim Example

• Answer
• The engine is operating OK now because the PCM
  has compensated for a slightly lean air-fuel
  mixture by increasing the injector pulse-width by
  about 14.
• Look for a vacuum leak or low fuel pressure.

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Fuel Trim Cells

• Computers use 16 or more cells for fuel trim
  corrections.
• Look at the fuel trim numbers in the cell where
  the problem is occurring.
• For example, looking at the fuel trim numbers at
  idle, will not show what is happening under a
  load at highway speed.

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Vortec Fuel Delivery
60PSI
55PSI
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Test Drive Analysis Flat-Rate Style

• Low power complaint
• Drive will consist of WOT.
• You must check the oil level first!
• Watch MAP and O2 sensor reaction.

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Test Drive Analysis

• MAP does not go high (4.6-4.8 volts) there is an
  intake restriction.
• Look for clogged air passages.
• O2S voltage goes low the fuel system is likely
  going lean.
• Look for a weak pump or a clogged fuel filter.

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Step 9KOEO Oxygen Sensor Test

• Look at O2S sensor voltage when the engine is
  cold and the ignition is first turned on.
• The heaters will cause the O2S to become
  conductive and the bias voltage will be gradually
  lowered as the sensors heat.
• Look for a sensor that fails to achieve a voltage
  of less than 100 mV after three minutes.

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KOEO O2S Test (continued)
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Carefully watch the bias voltage sent to the
oxygen sensors by the vehicle computer as the
ignition is turned on (engine off). As the
heater inside the oxygen sensors works, the
sensors become more conductive to ground and the
voltage should drop.
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After about three minutes, all sensors should
show about the same low voltage. A sensor that
remains high could be the cause of a hard-to-find
driveability problem, yet not trigger a
diagnostic trouble code (DTC).
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KOEO O2S Test

• A post-catalytic converter O2S will cause a
  driveability concern because the primary function
  of OBD II is to control exhaust emissions. If
  the rear O2S goes high, the PCM will try to make
  it go low by removing fuel, which can cause a
  driveability concern and no DTCs.
• The downstream HO2S causes the PCM to set the
  target air-fuel ratio needed by the catalytic
  converter.

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Lambda (Greek Letter)

• Lambda of 1.0 represents an air-fuel ratio of
  14.71.
• Lambda lower than 1.0 means the mixture is rich.
• Lambda higher than 1.0 means a leaner mixture.
• Multiply 14.7 times Lambda to get the air-fuel
  mixture.

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Commanded Lambda
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Step 10Snap Shot Testing

• Use a scan tool to record events over time.
• Trigger manually recommended for most cases (can
  be set to trigger when a DTC is set).
• Look at the data by scrolling through all data.

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Step 11Plot Snap Shot Data

• Select high- authority sensors (MAP, MAF, O2S,
  TP)
• Look at the plots.

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Plotting Snap Shot Data

• The trick is to look at the range of sensor
  values along the side.
• The range represents the high and the low values
  recorded for that sensor.

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Summary

• Teach a procedure that includes generic, as well
  as, enhanced scan tool usage.
• State normal sensor values.
• Use data plotting as a min/max feature.
• Use fuel trim numbers for fuel delivery diagnosis.

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Thats All Folks!
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Jim Halderman145 Golfwood Drive Dayton, OH
45449(937) 859-4107jim_at_jameshalderman.com