Generic OBD-II Operations

Transcription

1 Generic OBD-II Operations This chapter explains how to test 1994 later OBD-II vehicles. Most vehicles are equipped with two testing modes: Generic OBD-II and Enhanced OBD-II. The EPA requires all 1996 later vehicles sold in the USA to meet OBD-II standards. Some vehicles may appear to be OBD-II equipped, they may not be fully compliant. Check the VECI label to determine if a vehicle is an OBD-I or OBD-II model. The following information and procedures are specific testing in Generic OBD-II mode. For general scan tool testing information, see the user s manual for your diagnostic tool OBD-II and What it Means The term OBD stands for On Board Diagnostics. OBD-II is a system that the Society of Automotive Engineers (SAE) developed in order to standardize automotive electronic diagnosis so technicians could use the same scan tool to test any make and model without special adapters. The SAE established guidelines that provide the following: A universal diagnostic test connector, known as the data link connector (DLC), with dedicated pin assignments. A standardized location for the DLC, visible under the dash on the driver's side. A standardized list of diagnostic trouble codes (DTCs). The ability of the vehicle system to record a snapshot of operating conditions when an emissions-related fault occurs. Expanded diagnostic capabilities that record a code whenever a condition occurs that affects vehicle emissions. The ability to clear stored codes from vehicle memory with the scan tool. A glossary of standard terms, acronyms, and definitions used for system components. In addition, SAE has published hundreds of pages defining a standard communications protocol that establishes the hardware, software, and circuit parameters of OBD-II systems. Unfortunately, the vehicle manufacturers have different interpretations of this protocol. As a result, the generic OBD-II communications scheme used varies, depending on the vehicle. SAE publishes recommendations, not laws, but the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) made many SAE recommendations legal requirements, which were phased in over a three-year period. Beginning in 1994, vehicles with a new engine management computer were supposed to comply with OBD-II standards. For 1995, OBD-II systems were to appear on about 40% of the new vehicles sold. The government granted waivers for some OBD-II systems to give manufacturers time to fine-tune their systems. Beginning with the 1996 model year, all new vehicles sold in the USA must be fully OBD-II compliant. 239

2 Selecting The Generic Test Mode 17.2 Selecting The Generic Test Mode The OBDII GENERIC selection is available from the Manufacturer Selection menu (Figure 17-1). SCROLL TO SELECT A MANUFACTURER >SUBARU ( ) TOYOTA ( ) OBDII GENERIC ( ) Figure 17-1 Sample Manufacturer Selection menu z To select the Generic Test mode: Select OBDII GENERIC. The scan tool displays connection instructions (Figure 17-2). CONNECT OBD-II ADAPTER WITH K2 TO 16-PIN OBD-II DIAGNOSTIC CONNECTOR. NO REPAIR TIPS AVAILABLE IN GENERIC MODE. PRESS Y TO CONTINUE. Figure 17-2 Connection instructions 17.3 Connecting To The Vehicle The 16-pin OBD-II adapter (MT ) is used to connect the scan tool to the DLC (Figure 17-3). The adapter attaches to the end of the data cable with captive screws. NOTE: i The K-2A Personality Key must be inserted into the adapter for testing in the generic mode. The DLC is a 16-pin connector. The female half is on the vehicle, and the male end is on the scan tool cable. The connector is D-shaped and keyed so the two halves mate only one way. Pins are arranged in two rows of eight, numbered 1 to 8 and 9 to 16 (Figure 17-4). Figure pin OBD-II test adapter Figure 17-4 DLC configuration 240

3 Table pin OBD-II connector pinout PIN FUNCTION PIN FUNCTION 1 Manufacturer s discretion 9 Manufacturer s discretion 2 Bus+ Line, SAE J Bus- Line, SAE J Manufacturer s discretion 11 Manufacturer s discretion 4 Chassis ground 12 Manufacturer s discretion 5 Signal ground 13 Manufacturer s discretion earlier: Manufacturer s discretion 2003 later: ISO CAN The DLC cannot be hidden behind panels and must be accessible without the use of tools. (Figure 17-5). Although out of the normal line of sight, the DLC should be clearly visible to a crouching technician earlier: Manufacturer s discretion 2003 later: ISO CAN 7 K-line, ISO L-line, ISO Manufacturer s discretion 16 Vehicle battery positive Figure 17-5 OBD-II diagnostic connector location If the DLC is not visible, you may find a manufacturers sticker on the lower steering column cover, or below the left side of the dash center, indicating the DLC location. The DLC is designed for scan tool access only. You cannot jumper any of the terminals to display codes on the instrument cluster warning lamp, or malfunction indicator lamp (MIL). z To connect to a vehicle: Follow the on-screen connection instructions (Figure 17-2 on page 240) and press Y. The Main Menu displays (Figure 17-6). MAIN MENU--ENGINE >CODES AND DATA MENU CUSTOM SETUP [PRESS N FOR HELP] Figure 17-6 Sample Main Menu 241

4 Main Menu Selections 17.4 Main Menu Selections There are up to three main menu choices in Generic Testing Mode: CODES AND DATA MENU displays a sub-menu of choices for viewing parameter data, diagnostic trouble codes (DTCs), and various oxygen sensor (O2S) signal characteristics. CUSTOM SETUP configures scan tool settings, see the manual for your diagnostic tool. REVIEW MOVIE appears on a menu only after a movie is recorded. The Review Movie feature works the same in Generic Testing Mode as with specific manufacturers. See the manual for your diagnostic tool for details Codes and Data Menu This selection is available from the MAIN MENU in Generic OBD-II mode. Select CODES AND DATA MENU and a sub-menu (Figure 17-7) displays. CODES AND DATA MENU >CODES ONLY O2 MONITORS PENDING CODES DATA (NO CODES) FREEZE FRAME Five menu choices are available: Figure 17-7 Codes and Data Menu CODES ONLY displays diagnostic trouble codes (DTCs). O2 MONITORS displays various signal characteristics of O2S response. PENDING CODES displays codes that occurred once, but must occur again before a DTC is set. DATA (NO CODES) displays various sensor, switch, and actuator inputs and outputs. FREEZE FRAME displays certain data parameter readings that the vehicle stores when a DTC is set. Scan Tool Communication The selections from the Codes and Data Menu require that the scan tool communicate with the powertrain control module (PCM). The ignition must be on to establish communication. After making a selection, the scan tool displays the message in Figure WAITING FOR PCM TO COMMUNICATE WITH SCANNER Figure 17-8 Waiting to communicate message If communication is not established within 5 seconds, the scan tool displays the message in Figure 17-9 on page

5 NO COMMUNICATION. IS KEY ON? IS DLC CONNECTED? WAIT 15 SECONDS. PRESS N TO REENTER VEHICLE IDENTIFICATION OR SEE REFERENCE MANUAL. Figure 17-9 No communication message This message stays on the screen until communication is established, or until N is pressed. When communication is established, the scan tool will go to the selected function. Interrupted Communication If communication is interrupted during testing, but power remains connected, a No Communication message displays (Figure 17-9). This could happen if the connection to the vehicle is loose or the ignition is turned off. This message stays on the screen until communication is reestablished, or until N is pressed. Codes Only This selection displays DTCs in a standard, 5-character alphanumeric format. The first character, a letter, defines the system where a code was set, or displays U if there is a communication fault (Table 17-2). Table 17-2 First DTC character indications 1 st DTC CHARACTER SYSTEM WHERE A CODE WAS SET P B C U Powertrain Body Chassis Network The second character will be a 0, 1, 2, or 3 (Table 17-3). The meaning of a 2 or 3 varies according to the system character (P, B, C, or U). Table 17-3 Second DTC character indications 2 nd DTC CHARACTER TYPE OF CODE 0 SAE-defined (generic) code 1 Manufacturer-defined (enhanced) code P2 = SAE-defined (generic) code P3000-P3399 = Manufacturer specifications 2 & 3 P3400-P3899 = Reserved by SAE for future use B2 & C2 = Reserved for manufacturers B3 & C3 = Reserved by SAE for future use 243

6 Main Menu Selections The third DTC character indicates the system where the fault occurred (Table 17-4): Table 17-4 Third DTC character indications 3 rd DTC CHARACTER SYSTEM WHERE FAULT OCCURRED 1 Fuel or air metering problem 2 3 Ignition malfunction or engine misfire 4 Auxiliary emission control system problem 5 Vehicle or idle speed control system problem 6 Computer or output circuit fault 7 Transmission control problem 8 The final characters in the DTC tell you the conditions that triggered the code. Different sensors, actuators and circuits are assigned blocks of numbers; and the lowest number in the block indicates a general malfunction. This is the generic DTC. Higher numbers in the assigned block called enhanced codes provide more specific information, such as low or high voltage, slow response, or an out-of-range signal. Code Clearing Clear trouble codes from PCM memory through the scan tool. The CLEAR CODES selection is available from the Codes Only Exit menu, but not from the Data (No Codes) Exit menu. z To clear the codes: 1. Press N from any codes display. The Exit menu displays. 2. Select CLEAR CODES. The scan tool returns to the CODES ONLY mode, and the display indicates that codes are cleared by stating NO CODES PRESENT. If the code-clearing operation fails for any reason, the previous codes reappear. If this occurs, press N to return to the EXIT menu and repeat the CLEAR CODES operation. O2 Monitors This selection lets you view various 02S signal response characteristics. There are two different monitors: one for pre-converter sensors and one for post-converter sensors. The PCM looks for three main things from the pre-converter oxygen sensor: Maximum voltage Minimum voltage Switching rate The PCM looks for the sensor signal to rise above 600 millivolts, fall below 300 millivolts, and switch in less than 100 milliseconds to monitor the pre-converter O2S. The PCM performs a 244

7 fuel control routine and examines the pre-converter sensor readings during known air/fuel mixtures. The PCM looks for specific sensor values, based on the mixture levels it provides. The post-converter check is significantly different. The PCM sees almost no switching when the converter is functioning properly. To test the sensor, the PCM forces a fuel control routine that the converter cannot compensate for, and then monitors the sensor response. Both sensors are also monitored continuously for open and short circuits. Select O2 MONITORS and a screen similar to Figure displays. SCROLL TO SELECT A TEST: >RICH TO LEAN SENSOR THRESHOLD VOLTAGE LEAN TO RICH SENSOR THRESHOLD VOLTAGE LOW SENSOR VOLTAGE FOR SWITCH TIME CALC Figure Sample O2 Monitors screen There are 9 sensor response signal tests available (Figure 17-11). Rich H D B A C G Lean F E I Figure O2 sensor monitor tests A Test 1: Rich to lean sensor threshold voltage B Test 2: Lean to rich sensor threshold voltage C Test 3: Low sensor voltage for switch time calculation D Test 4: High sensor voltage for switch time calculation E Test 5: Rich to lean sensor switch time F Test 6: Lean to rich sensor switch time G Test 7: Minimum sensor voltage for test cycle H Test 8: Maximum sensor voltage for test cycle I Test 9: Time between sensor transitions Pending Codes Pending codes set when operating conditions are out of the normal range, but not all the criteria to set a DTC occur. For example, a failure must occur on two consecutive trips or drive cycles before certain OBD-II codes set. In this case, a pending code is recorded during the first trip when the failure first occurs. 245

8 Main Menu Selections Data (No Codes) OBD-II vehicles transmit PCM operating data to the scan tool, but do not DTCs in this mode. The scan tool does not affect PCM operation, and the vehicle can be driven normally for road testing (Figure 17-12). Use the CODES ONLY selection to read DTCs. OBD II DATA ** DATA (NO CODES). OK TO DRIVE ** (NO CODES AVAILABLE IN THIS MODE) ENGINE 0 THROTTLE(%) 0.0 Figure Sample Data (No Codes) display Freeze Frame This selection lets you view certain data parameter readings that the vehicle stores the instant that a code (DTC) is set. Parameters displayed will vary, depending on the code. 246