OBD SYSTEMS
OBD II
"OBD" is an acronym for the On Board Diagnostic System.
California OBD II applies to all gasoline engine vehicles up to 14, 000 lbs. Gross Vehicle Weight Rating (GVWR) starting in the 1996 MY and all diesel engine vehicles up to 14, 000 lbs. GVWR starting in the 1997 MY.
Several states in the Northeastern United States have chosen to adopt the California emission regulations starting in the 1998 MY and are known as "Green States".
Green States receive California-certified vehicles for passenger cars and light trucks up to 6, 000 lbs. GVWR. Starting in the 2004 MY, Federal vehicle over 8, 500 lbs. will start phasing in OBD II.
Starting in 2004 MY, gasoline-fueled Medium Duty Passenger Vehicles (MDPVs) are required to have OBD II. Federal OBD II applies to all gasoline engine vehicles up to 8, 500 lbs. GVWR starting in the 1996 MY and all diesel engine vehicles up to 8, 500 lbs. GVWR starting in the 1997 MY.
OBD II system implementation and operation is described in the remainder of this document.
MALFUNCTION INDICATOR LAMP ILLUMINATION
"MIL" is an acronym for the Malfunction Indicator Lamp.
If the ECM recognizes a malfunction that leads to increased emissions values, it indicates them by lighting the MIL which is located in the instrument cluster.
The ECM switches on the MIL after the ignition is switched on. Shortly after the engine is started, The MIL goes out if the ECM does not detect a malfunction that increases the emissions values.
If the ECM recognizes a malfunction that leads to increased emissions during the operation of the engine, the ECM switches on the MIL and an entry is stored in the DTC memory of the ECM.
CAN DATA LINK
"CAN" is an acronym for Controller Area Network.
The ECM communicates with all databus capable control modules by a CAN Data Link.
The databus capable control modules (i.e. Engine Coolant temperature Sensor) are connected by two data bus wires which are twisted together (CAN_High and CAN_Low), and exchange information (messages) to the ECM. Missing information on the databus is then recognized and stored as a malfunction.
The ECM illuminates the MIL through the CAN data link and tells the MIL to turn on, turn off, or blink.
ELECTRONIC POWER CONTROL WARNING LAMP
"EPC" is an acronym that stands for the Electronic Power Control (E-gas).
The ECM monitors all EPC components after the ignition is switched on.
If a malfunction is recognized in the EPC system during the operation of the engine, the ECM switches on the EPC which is located in the instrument cluster and an entry is stored in the DTC memory of the ECM.
PRELIMINARY CHECK
Before performing any pin point test or component diagnosis, a Preliminary Check must be performed.
Connect the scan tool.
Switch the ignition on.
Using the scan tool, check for any stored or related DTC's.
If other DTC's are stored
Repair these DTC's first before performing the following procedure.
If no other DTC's are stored
Using the scan tool, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
Perform a road test to attempt to duplicate the customers complaint.
If the DTC returns
Perform the diagnostic procedure.
If the DTC does not return
The fault is intermittent or a sporadic condition may exist.
Check the suspected component, electrical harness and electrical harness connectors for damage, corrosion, loose or broken terminals.
If necessary, repair the faulty wiring connection.
Perform a road test to verify the repair.
If the DTC returns
Perform the diagnostic procedure.
If the DTC does not return
The fault may have been the result of a loose electrical connection.
Generate readiness code. Refer to READINESS CODE DESCRIPTION .
End of diagnosis.
READINESS CODE
The following table provides quick links to all instructions in this article.
| READINESS CODE DESCRIPTION . |