Description and Operation

OBD-II Overview

1. Overview The California Air Resources Board (CARB) began regulating On-Board Diagnostics (OBD) for vehicles sold in California starting with the 1988 model year. The first stage, OBD-I, required monitoring of the fuel metering system, exhaust gas recirculation (EGR) system, and additional emission-related components. The Malfunction Indicator Lamp (MIL) was required to illuminate to warn the driver of a malfunction and the need for emission control system repair. Associated with the MIL was a Trouble Code or Diagnostic Trouble Code (DTC) identifying the specific location of the malfunction. The OBD system was proposed by CARB to improve air quality by identifying vehicles exceeding emission standards. The adoption of amendments to the Federal Clean Air Act in 1990 also prompted the Environmental Protection Agency (EPA) to develop On-Board Diagnostic requirements. CARB OBD-II rules were followed until 1999, when federal rules were used. The OBD-II system complies with government standards by monitoring the emission control system. When a system or component exceeds an emission threshold or operates outside its tolerance, a DTC is stored and the MIL illuminates. The Diagnostic Executive is a computer program in the Engine Control Module (ECM) or Powertrain Control Module (PCM) that coordinates the OBD-II self-diagnostic system. This program controls all monitors and interactions, DTC and MIL operation, freeze frame data, and the scan tool interface. Freeze frame data describes the stored engine conditions, such as engine status, fuel control status, spark, RPM, load, and warm-up status at the point where a malfunction is first detected. Previously stored conditions will be overwritten only if a fuel or misfire malfunction is detected. This data is available through the scan tool to assist vehicle repair. The center of the OBD-II system is a microprocessor called the Engine Control Module (ECM) or Powertrain Control Module (PCM). The ECM or PCM receives data from sensors and other electronic components (switches, relays, etc.). Based on the information received and programmed in its memory (keep-alive memory and others), the ECM or PCM generates output signals to control various relays, solenoids, and actuators. 2. Hardware Configuration and Related Terms 1) GST (Generic Scan Tool)

2) MIL (Malfunction Indicator Lamp) - MIL transistor operation

The Malfunction Indicator Lamp (MIL) is connected to the ECM or PCM connector. The MIL is supplied from the battery (open-collector driver). In most vehicles, the MIL is installed on the instrument panel. The lamp driver cannot be damaged by a short circuit. Lamps with power dissipation much higher than the total power dissipation of the MIL and the lamp in the tester may cause a malfunction indication. ▷ With the ignition ON and engine speed (rpm) < MIN. RPM, the MIL switches ON for a visual check by the driver. 3) MIL Illumination When the ECM or PCM detects an emission-related malfunction during the first driving cycle, the trouble code and engine data are stored in freeze frame memory. The MIL illuminates only when the ECM or PCM detects the same malfunction associated with the trouble code in two consecutive driving cycles. 4) MIL Extinguishing ● Misfire and fuel system malfunctions: For a misfire or fuel system malfunction, the MIL may be turned off if the same malfunction is not detected during monitoring in three consecutive driving cycles in which conditions are similar to those under which the malfunction was first detected. ● All other malfunctions: For all other malfunctions, the MIL may be turned off after three consecutive driving cycles during which the monitoring system responsible for illuminating the MIL operates without detecting the malfunction, and no other malfunctions have been identified that would independently illuminate the MIL in accordance with the requirements described above. 5) Clearing Trouble Codes The diagnostic system may erase a trouble code if the same malfunction is not re-registered in at least 40 engine warm-up cycles, while the MIL is not illuminated. 6) Controller Area Network (CAN) Communication Line

• Bus Topology: Line (bus) structure
• Wiring: Twisted pair
• DLC External Cable Length: 5 m max.
• Data Transfer Rate
• Diagnostics: 500 kbps
• Service mode (reprogramming, VIN write): 500 kbps or 1 Mbps

7) Driving cycle. A driving cycle consists of engine start and engine shutdown. 8) Warm-up cycle. A warm-up cycle means sufficient vehicle operation such that the engine coolant temperature has risen at least 40 °F (22 °C) from engine starting and reaches a minimum temperature of at least 160 °F (70 °C). 9) Trip. A trip is vehicle operation (after an engine-off period) of sufficient duration and driving mode such that all components and systems are monitored at least once by the diagnostic system, except for catalyst efficiency or evaporative system monitoring when a steady-state (constant speed) check is used, subject to the limitation that all manufacturer-defined disablement conditions must be met at least once during the first part of the engine start of the applicable FTP cycle. 10) Diagnostic trouble code format.

• Diagnostic Trouble Code (SAE J2012)
• DTCs used in OBD-II vehicles begin with a letter followed by four numbers.

The first letter of the diagnostic trouble code identifies the function of the controlled device that has malfunctioned. The letter "P" indicates a powertrain device, "C" indicates a chassis device, "B" indicates a body device, and "U" indicates a network or data communication circuit. The first digit indicates whether the code is generic (common to all manufacturers) or manufacturer-specific. "0" and "2" mean generic; "1" indicates manufacturer-specific. The second digit indicates the affected system, with a number from 1 to 7. The list below shows which numbers are assigned to each system.

1. 1
   Fuel and Air Metering
2. 2
   Fuel and Air Metering (injector circuit malfunction only)
3. 3
   Ignition System or Misfire
4. 4
   Supplemental Emission Control Monitors
5. 5
   Vehicle Speed Control and Idle Control System Monitors
6. 6
   Computer Output Circuits
7. 7
   Infection Transmission

The last two digits of the diagnostic trouble code indicate the component or section of the system where the malfunction is located. 11) Freeze frame data. When a freeze frame event is triggered by an emissions-related DTC, the ECM or PCM stores various vehicle information as it existed at the time the malfunction occurred. The DTC number together with the engine data can be useful to the technician in determining the cause of the malfunction. After the 1st driving cycle data for a DTC is stored in freeze frame memory, it remains there even when the malfunction occurs again (2nd driving cycle) and the MIL illuminates.

• Freeze Frame List

a.	Calculated Load Value

b.	Engine Speed

b.

Fuel Trim

d.	Fuel Pressure (if available)

e.	Vehicle Speed (if available)

f.	Engine Coolant Temperature

g.	Intake Manifold Pressure (if available)

h.	Closed Loop or Open Loop Operation

I.	Malfunction Code

3. OBD-II Readiness Monitors 1) Catalyst Monitor. The catalyst monitor is a self-diagnostic strategy in the ECM or PCM that uses the heated oxygen sensor (HO2S) downstream to determine when the catalyst has dropped below its minimum efficiency in its ability to control exhaust emissions. 2) Misfire Monitor. A misfire is defined as the lack of proper combustion in the cylinder due to absence of spark, poor fuel metering, or poor compression. Any combustion that does not occur in the cylinder at the proper time is also a misfire. The misfire detection monitor detects misfires due to fuel, ignition, or mechanical causes. The purpose is to protect the catalyst from irreversible damage and to warn the customer of an emission failure or inspection/maintenance failure by illuminating the MIL. When a misfire is detected, special software called freeze frame data is activated. Freeze frame data records the operating conditions of the vehicle when a fault is detected by the misfire detection monitoring strategy. 3) Fuel System Monitor. The fuel system monitor is a self-diagnostic strategy in the ECM or PCM that monitors the adaptive fuel table. The fuel control system uses the adaptive fuel table to compensate for normal variability of fuel system components caused by wear or aging. During normal vehicle operation, if the fuel system appears to be biased lean or rich, the adaptive value table shifts the fuel delivery calculations to remove the bias. 4) Engine Cooling System Monitor. The cooling system monitor is a self-diagnostic strategy in the ECM or PCM that monitors the ECTS (Engine Coolant Temperature Sensor) and thermostat for circuit continuity, output range, and rationality faults. 5) O2 Sensor Monitor. OBD-II regulations require monitoring of the upstream heated oxygen sensor (HO2S) to determine whether sensor deterioration has exceeded threshold values. In addition, the HO2S is located downstream of the warm-up three-way catalytic converter (WU-TWC) to determine catalyst efficiency. Although the downstream HO2S is similar in type to the one used for fuel control, it functions differently. The downstream HO2S is monitored to determine whether voltage is generated. This voltage is compared with the calibrated allowable range. 6) Evaporative Emission Control System (EVAP) Monitor. The monitor is a self-diagnostic strategy within the ECM or PCM that checks the integrity of the EVAP system. The complete evaporative system detects leaks or combined leaks equal to or greater than a leak caused by a 0.040 inch and 0.020 inch orifice. 7) Air Conditioning System Monitor. The air conditioning monitor is a self-diagnostic strategy in the ECM or PCM that monitors the malfunction of all air conditioning system components when the A/C is switched on. 8) Comprehensive Component Monitor. The comprehensive component monitor is a self-diagnostic strategy in the ECM or PCM that detects malfunctions of any electronic components or transmission system that provide input to the ECM or PCM and are not exclusively input to any other OBD-II monitor. 9) Air Conditioning Component Monitoring Requirement: If the vehicle includes an engine control strategy that changes fuel delivery at idle and/or spark control while the air conditioning system is on, the OBD II system must monitor all electronic air conditioning system components for malfunctions that prevent the system from causing alternative control when the A/C system is on, or cause the system to activate alternative control while the A/C system is off. In addition, the OBD II system must monitor malfunctions of all electronic air conditioning system components that are used as part of the diagnostic strategy for any other monitored system or component. Implementation Plan: There is no built-in engine control strategy that changes fuel and/or spark control when the air conditioning system is on. Malfunctions of air conditioning system components are not used as part of the diagnostic strategy for another monitored system or component.