The Bureau of Automotive Repair Presents: The 2007 Smog Check Technician Update Course written by Wayne Brumett
This course will provide an overview of the following: • Review of Computer Control Systems Interaction and Advanced Fuel Trim Diagnostics. • Networking and Controller Area Network (CAN). • OBD II - Mode 6 Diagnostics. • OBD II Evaporative Emission Control Systems. • Technical Service Bulletins and using Manufacturers’ Internet sites. • Computer Program Re-flashing. • BAR Program Updates.
NOTICE TO TECHNICIANS:BAR update courses are designed to provide Smog Check Technicians with Information on Program Changes and New Technology that can Affect the Smog Check Program. This course is not designed to teach you in-depth information on a particular subject area (e.g. Mode 6, EVAP Diagnostics, CAN, etc.). As a professional automotive technician, you are expected to educate yourself (i.e. attend courses, read publications & training manuals, etc.) to complement your understanding of this training course material.
To pass this course, you must: • Read the entire course textbook (prior to the course). • Read the two Motor Magazine articles (supplied by your school/instructor) on “CAN” and evaporative (EVAP) system diagnosis. • Turn in for credit the 50 question quiz in the textbook on the first day of class. • Successfully complete all the laboratory examinations. • Attend all course hours. • Pass the written final examination (with a score of 70% or better).
Engine Control System Operating Strategy - Overview - The Input/Output Relationship
Introduction Engine Control System Operating Strategy is: A programmed strategy in the Powertrain Control Module (PCM), that determines how sensor input information will be calculated, and what PCM output commands will be sent to the various actuators that control vehicle operation, based on those sensor inputs. As a technician, it is important for you to understand the relationship between input values and output commands.
Introduction If the input signal to the PCM is inaccurate, then the command from the PCM to the actuator(s) to control the vehicle will also be inaccurate. Garbage In = Garbage Out =
Review of Sensor/PCM Interaction • The following information is the minimum needed for the engine controller to properly control the air/fuel mixture and ignition timing events: • Engine RPM • Engine Load (MAP / MAF) • Driver Demand (TPS) • Engine Coolant Temperature (ECT) • Barometric Pressure (BARO) • Intake Air Temperature (IAT) • Vehicle Speed (VSS) • Battery Voltage • Oxygen Sensor (O2 - used for fine tuning)
Sensor/PCM Interaction - Review • Calculating basic injector pulse width: • Engine RPM • Engine Load (MAP / MAF) • Sensor inputs used to modify basic pulse width: • Driver Demand (TPS) • Barometric Pressure (BARO) • Engine Coolant Temperature (ECT) • Intake Air Temperature (IAT) • Vehicle Speed (VSS) • Battery Voltage • Oxygen Sensor (used for fine tuning)
Sensor/PCM Interaction - Review • Injector pulse width is calculated based on sensor inputs, and fine tuned utilizing the oxygen sensor input(s). • The computer compensates for variations in engine mechanical, electrical and sensor tolerances that develop over the vehicle life span, using Long Term Fuel Trim (LTFT) and Short Term Fuel Trim (STFT) values. • LTFT corrections are made to move STFT towardsthe middle of the fuel correction scale.
Sensor/PCM Interaction - Review The computer operates in either Open or Closed loop. • Open Loop: • The oxygen sensor is ignored and signals from the other sensors, that are used to provide a basic pulse, are evaluated. The computer matches these conditions with values stored in memory (look-up tables) and issues commands to outputs devices (e.g. injector pulse width, timing advance, etc.). • Closed Loop: • The computer now evaluates the oxygen sensor input signal, and issues output commands to fine tune the fuel mixture.
51 102 179 77 26 205 154 230 -60% -80% -40% -20% +20% +40% +60% +80% = Long Term Fuel Trim (LTFT) = Short Term Fuel Trim (STFT) Fuel Trim Operation Adaptive “Learned” Fuel Correction LTFT Subtracting Fuel Adding Fuel Subtracting Fuel 0 10% 10% STFT Now Moves to Middle Long Term Fuel Trim When the Engine Goes Rich, The STFTSubtracts Fuel. If it Cannot Adust Enough, the LTFT Makes a (-) Adjustment to Bring STFT Back into Operating Parameters Short Term and Long Term Fuel Trim Usually Operates Within the 0 – 10% (+/-) Range, When There are No Engine Performance Problems.
An Excessive Increase in Fuel Trim May Be Due To: Fuel starvation (restricted filter, low pump pressure, etc.) Ignition system problems (i.e., misfires) Vacuum leak Mechanical problems AIR System moving air up stream during closed loop Upstream Exhaust leak False Sensor Readings (MAF/MAP, O2, etc.) An Excessive Decrease in Fuel Trim May Be Due To: Excessive fuel Pressure Restricted Air flow Leaking Injectors False Sensor Readings (MAF/MAP, O2, etc.) Fuel Trim Diagnostics
Sensor/PCM Interaction – Look Up Tables So how does the PCM make the decision on how to adjust the fuel, ignition timing, and when to turn on/off the actuators? The PCM is programmed from the factory with a series of mathematical algorithmic “look up tables.” These look up tables are similar to the multiplication tables you learned in grade school, only much more evolved.
Sensor/PCM Interaction – Look Up Tables In this multiplication table, when you converge the outside numbers you want to multiply, you find the answer. Example: 3 X 3 = 9
Load Increase CELL Sensor/PCM Interaction – Load Cell Load Cell: An embedded program in the Look Up Table that determines fuel delivery and timing from RPM/load sensor inputs Using this multiplication table principle, lets build a simple load cell table, using just two inputs to determine the injector pulse width and ignition timing for a simple (theoretical) engine. As the throttle opens, more air enters the engine. The Mass Air Flow (MAF) sensor records the increase in air entering the engine. Based on the engine speed (RPM) and MAF readings (load), the look up table assigns preset commands for injector pulse width and ignition timing.
Sensor/PCM Interaction – Look Up Tables Of course, there are many sensor inputs that the PCM receives. The PCM, based on the inputs it receives, has to find a matching cell (as close as possible) in the ‘Look Up Table.” The PCM issues output commands (based on the selected cell) to operate the vehicle. PCM LOOK UP TABLE PCM Receives Inputs PCM Sends Output Commands to Actuators Based on the Cell Selected PCM Selects Cell PCM Selects Closest Cell Match
Sensor/PCM Interaction – Adaptive Strategy Have you ever heard of this situation before? A technician diagnoses a bad throttle position sensor (shows 2 volts at idle) as the reason for high engine idle and engine performance/emission problems. He installs a new sensor, but the vehicle still runs poorly – why? Answer: The technician did not reset the PCM’s adaptive strategy.
Sensor/PCM Interaction – Adaptive Strategy An “Adaptive Strategy” is programmed into a PCM’s “Keep Alive Memory” (KAM) to allow the computer to adapt to deteriorating component conditions (i.e., sensors, actuators, worn parts, etc.) and a driver’s driving habits. This programmed strategy allows the PCM to adapt (learn) to use abnormal inputs, and still allow the vehicle to operate within a normal vehicle performance range (within reason). The KAM will maintain this “learned” strategy as long as it is supplied battery voltage.
Sensor/PCM Interaction – Adaptive Strategy In our scenario with the bad TPS, the technician, after completing the TPS repairs, did not clear the old TPS (adaptive strategy) information from the KAM (using the scan tool or disconnecting the battery). The PCM was still using the stored (erroneous) information it learned (adapted) from the old defective part (2 volts at idle) to run the system. This is why the vehicle still performed poorly after the repair.
Sensor/PCM Interaction – Adaptive Strategy Eventually, the PCM would have learned (adapted) to the new TPS input values (after a series of drive cycles), and returned to normal operation. By not resetting the PCM adaptive strategy, the customer would be upset when the vehicle was returned to them as having been “repaired,” but still ran poorly. Telling the customer to “just drive the car and it will get better” probably won’t set too well with your customer.
O2 Sensor Reflects A Rich Condition (high voltage Signal) 2 STFT is Now Within 5% 3 STFT Reacts to the High O2 Sensor Voltage with a (-) 10 adjustment 5 LTFT Adjusts Down To Bring STFT closer to “0” Adaptive Strategy Program Initially Assigns a +7 LTFT Value 1 4 TIME BASE LTFT Adaptive Strategy The PCM has the ability to adjust to the driving habits of the driver. In this scenario, we will see how the Long term Fuel Trim (LTFT) is adjusted due to changes in the oxygen sensor and Short Term Fuel Trim (STFT). This Adaptive Cell has Now Been Corrected to This New LTFT Value
Speed Density Long Term Adaptive Cells Let’s see this adaptive strategy in action. In the next 5 scan tool screens, we will see the fuel trim cells for a 2000 Dodge Intrepid with a 3.5L engine, as viewed on a Chrysler DBR II scan tool. Based on inputs, the PCM selected Fuel Trim Cell #: C12. The cell is commanding a negative (-) 4 % trim (adapted strategy). On this vehicle, during openloop operation, LTFT is used to establish injector pulse width. Note that STFT is zero. Open Loop Engine Speed is 795 RPM (Idle) Trans in Drive Injector Pulse Width is 2.8 mS Long Term Fuel Trim is (–) 4.1 (subtracting fuel) Short Term Fuel Trim Is at 0.0
Speed Density Long Term Adaptive Cells On this next screen, as the engine RPM increases above 1900, LTFT moves into the upper row of cells that have adapted to a previously learned condition. Note: Cells C4 & C5 are indicative of the load and RPM that would be used during an ASM test or Drive Cycle. With this load (MAP=11.9) and RPM (1919) O2 Reacts to engine conditions (high volts) STFT Repsonds to O2 with – 6.2% If STFT goes too negative, LTFT will adopt a more positive (+) strategy to add fuel for future use of this cell The PCM chose cell C5
Speed Density Long Term Adaptive Cells In this next screen, we see the results of a major fuel trim correction. The technician installed a new part, but did not reset the adaptive strategy. The PCM is using a learned value from the bad part (+13%) in cell C8. Since the problem has been corrected, the LTFT is now over fueling, and the STFT is making a major correction (-14%) to adapt to the new situation. LTFT Learned Value from Bad Part = + 12.7% It will take a couple of drive cycles for the system to adapt to the newly installed part, but the customer may complain about driveability problems. STFT Is trying desperately to reduce fuel trim = - 14.1%
Speed Density Long Term Adaptive Cells Note: Injector Pulse Width is now zero In this next sceen, the vehicle is decelerating and all fuel trim has been cut to zero With the throttle close, the PCM selects cell C15 to cut fuel delivery (- 7%)
Resetting Long Term Fuel Trim Cells In this next screen, we see that the technician has reset the adaptive fuel trim memory (via the scan tool). Note that all the fuel trim cells are now set to zero. With the system reset, the vehicle’s driver may notice that the vehicle’s throttle response may now be sluggish, until the system has time to adapt. Fuel Trim Cells Reset to Zero
- Review - As you can see, if sensor(s) input (e.g., MAF, TPS, IAT, ECT, etc.) is incorrect, the PCM will still try to match the (erroneous) inputs it receives to the closest matching cell. Due to the bad sensor input(s), the cell selected by the PCM will not be appropriate for the actual operating conditions of the vehicle. The vehicle may now experience an emission(s) failure/driveability problem. Example: If the wrong cell was selected by the PCM (e.g., using bad MAF info), that cell may not allow EGR activation; thus the vehicle may fail for NOx. If the correct cell were selected, the EGR would be activated, and the NOx problem would not be present.
- Review - - REMEMBER - • Garbage In = Garbage Out =
AUTOMOTIVE NETWORKS For many years, as vehicle manufacturers added new features to their vehicles, they had to add more sensors, actuators, and wiring to accommodate these new features. These additions added more complexity to the vehicle, and required a larger and more expensive central computer. For example, when electric cooling fans were first controlled by the OBD system, it was not uncommon for an engine to have three coolant temperature sensor/switches: one for the coolant temperature input to PCM, one for the electric cooling fan operation, and one for the coolant temperature warning light or gauge on the dash. These extra sensors/switches were redundant, and added weight (less fuel economy) to the vehicle, and added more potential for system failure (shorts, opens, etc.). To eliminate these problems, manufacturers changed to a network system.
AUTOMOTIVE NETWORKS When you use the internet, or use your ATM card at the bank or market, you are using a network system. This system shares information with other workstations (banks, internet providers, etc.) on a common carrier system (e.g. telephone or internet system). A Local Area Network (LAN) is a network that is contained to one local area, like your home, shop, or car. Car manufacturers have been using LAN systems on cars for years.
AUTOMOTIVE NETWORKS The advantage to having a LAN system are: • Eliminates hard wiring of sensors/actuators to every component (e.g. PCM, warning lights, fans, etc.), which results in lower production costs. • Eliminates redundant components and wiring, which reduces vehicle weight (better fuel economy). • Reduces potential system failures (shorts, opens, etc.), since there is less wiring. • Information transfer is faster between component systems.
CONTROLLER AREA NETWORK (CAN) NO, we are not talking about this kind of Can!
CONTROLLER AREA NETWORK (CAN) Most vehicle manufacturers are moving to a network system called “Controller Area Network” (CAN). This system will be required on all light duty vehicles sold in California by MY 2008. The advantage of this system is that all vehicles will have a standardized communication protocol, so your scan tool will be able to communicate with this high speed network system.
CONTROLLER AREA NETWORK So how does this “CAN” system work? In general, the system employs a “data bus” (bus) wire to carry individual information packets (sensor outputs, computer commands, etc.) throughout the network system. Think of this bus as a freeway, with on ramps and off ramps to cities (i.e., modules) that can exchange information. The cars are like information packets traveling the bus. Trans Module HVAC Module Dash Module Information Packet
CONTROLLER AREA NETWORK The CAN bus wire is usually a two wire configuration, with a positive (+) and negative (-) wire. Each wire is capable of transmitting information. The wire is twisted to reduce stray (induced voltage) signals coming into the bus wire from adjacent high voltage sources (e.g., secondary ignition wires, coils, etc.).
CONTROLLER AREA NETWORK (CAN) Connected to the bus are modules (most are programmable). These modules are like small computers. Most modules can receive information packets off of the bus (like sensor/actuator information –off ramps), and also send information packets (like on ramps) to travel on the bus, to be used by other modules. Using these modules eliminates the need to have large and expensive centralized computers.
CONTROLLER AREA NETWORK Modules can be placed at various locations on the vehicle, in close proximity to sensors, actuators, and components they serve. Since most modules are programmable, and use a standardized communication protocol, they can be programmed to accommodate any new sensor, actuator, or component the manufacturer chooses to add during updates - without extensive re-wiring. Module Bus Wire
CONTROLLER AREA NETWORK At this point, you might be asking yourself: “So how does all that information get transferred on a single (two wire) network? Isn’t there going to be a traffic jam of information going to and from the modules?”
CONTROLLER AREA NETWORK The Module Converts the Analog Temp Signal into a Digital Information Packet, to be Sent Out on the Bus. The Information Packet is Given a Priority Code. In this Case, it is Given a High Priority OK kid, You have got your priority code, now get on that bus and tell everyone who wants to know, that we have a big problem with the engine! Each module is programmed to emit it’s data, using an electronic code. This coded data packet is given a priority, based on how important it is to the operation of the vehicle. The Engine Temp Sensor Sends a HOT ENGINESignal to the Module
CONTROLLER AREA NETWORK Each module, commonly refereed to as a “slave” module, is connected to a “Master” module. The Master module sorts the information packets on the bus, and decides the order in which an information packet should be sent (via priority) on the bus (like a traffic officer). Some of the slave modules are in a sleep mode, and the Master module has to wake them up. The reason they are in the sleep mode is to reduce parasitic battery drain when the vehicle is not in use.
CONTROLLER AREA NETWORK The Master module will wake up a slave module for the following reasons: • Another module is requesting information that the sleeping module can provide (e.g., sensor/actuator information). • Another module is sending information that the sleeping module needs (e.g., actuator commands, etc.). • The Master module determined that more computing ability is needed to operate the vehicle, so it uses the computing resources of the sleeping module to assist in carrying out difficult computing functions (an additional computer resource).
CAN Bus Speed (in kbps) CONTROLLER AREA NETWORK There are three classes of CAN. The classes are defined by the Society of Automotive Engineers (SAE) based on data speed of the bus; measured in kilobytes per second (kbps): • CAN “A” – Has very slow data transference speed, at about 10 kbps. This class was used on early vehicle systems, but is seldom used today. • CAN “B” – Has medium data transference speed at about 83 - 125 kbps. This class is used for vehicle systems that don’t require exceptional data transference speed (e.g., body control module, HVAC module, etc.). • CAN “C” – Has high data transference speed, at about 500 - 1000 kbps. This class is used primarily on powertrain and chassis systems that require high data speed (e.g., electronically operated: throttle, steering, brakes, etc.). Usually, this system only has three modules (e.g., PCM, TCM, ABS).
CONTROLLER AREA NETWORK Most vehicles today employ the use of both CAN “B” and “C” bus systems to operate the vehicle. To allow these two bus systems, of vastly different data rate speeds, to share information with each other, the CAN system employ a “Gateway” module. The Gateway acts as an interface between the different buses (like an interpreter), which allows them to share information. Usually, the Master module and the Gateway module are incorporated into one unit. CAN “B” CAN “C” GATEWAY
CONTROLLER AREA NETWORK System Failure: If one of the two wires on the CAN “B” bus has a short/open, then the following mayhappen: • The system will still operate, but may not function as designed. System may be slow in operation. • Depending on where the short/open is located, some part of the system may not operate at all. • If a sensor input from a defective section cannot get a signal to a good module needing that sensor input, then that good module may not operate as designed (e.g., bad module attached to speed sensor may cause problems with PCM outputs).
CONTROLLER AREA NETWORK System Failure (con’t): • In a severe CAN “B” bus wire failure (both wires open/grounded), multiple system failures can occur. • Improper dashboard warning light operations may occur. • MIL will be illuminated.
CONTROLLER AREA NETWORK I GUESS THE BUS STOPS HERE! System Failure (con’t): The CAN “C” bus may be faster, but it is not as fault tolerant as the CAN “B” bus. Any shorts or opens maymake the system inoperable, and cause false dash readouts (e.g. engine temperature).