OBD II Modes: ($04) Clear Emissions Related Data

 OBDII is a set of standards and practices used to fine tune emission programs across vehicle makes and models. OBDII Mode 1 is for requesting and displaying current emission related scan data. Mode 2 is for requesting Freeze Frame data. Mode 3 is for requesting emission related trouble codes. 

Mode 4 is for clearing emission related data in modules that store OBDII information. Mode 4 is for clearing trouble codes, freeze-frame data and stored test data. Mode 4 also resets all the monitors and turns off the check engine light. 

Kenny@ggauto.repair

OBD II Modes: Mode 3 ($03) Request Emission Related Trouble Codes

OBDII is a set of standards and practices used to fine tune emission programs across vehicle makes and models. OBDII Mode 1 is for requesting and displaying current emission related scan data. Mode 2 is for requesting Freeze Frame data. OBDII is concerned with emission systems but understanding the system can often help with diagnostics. 

Mode 3 is for requesting emission related trouble codes. OBDII codes are prefaced with P0 and are defined by accepted definitions for Generic or Global OBDII. A query for OBD II codes should return the number of modules online responding and which module is responding. You won't get codes from modules other than those containing the OBDII emission data. 

This demo picture is showing 1 ECU module communicating via J1850 protocol and that it is the Engine Module. A Mode 3 request for codes returns the P0 prefixed codes for OBDII emission test failures.

Important to bear in mind when retrieving trouble codes is that they do not indicate parts that need replaced or what is wrong with the car. They indicate failed tests. Diagnostics are the steps you need to take to determine why the tests were failed. But, gathering data is part of the diagnostic method so it's a good start. 

Kenny@ggauto.repair

OBD II Modes: Mode 2 ($02) Display Freeze Frame Data

OBDII is a set of standards and practices used to fine tune emission programs across vehicle makes and models. We covered Mode 1 which is the ability to request current data display. Mode 1 data is actual data, not enhanced or altered. However, because OBDII is an emission standard and not actually a diagnostic program your available data items are limited.  

OBDII Mode 2 is the request of Freeze Frame data. When an OBDII trouble code is set a frame of data is captured at that time. Mode 2 allows the Freeze Frame to be called up for viewing. It can give an idea of the conditions that were present at the time of the fault. There are limited data items, and the frame is not a millisecond of data capture but over the period of a few seconds. Still, the information can often be helpful to diagnostics even though it isn't designed specifically for that. An example would be Freeze Frame for a lean fuel condition. If the Freeze Frame shows the code conditions to be heavy acceleration/ high fuel demand then you can suspect a fuel delivery problem. If the conditions were at idle or low fuel demand then you can suspect a vacuum leak. If you couple that vacuum leak with presence at cold engine temperature then you may even narrow that leak down to an intake manifold sealing problem. 

                                      

Kenny@ggauto.repair

 

Data Driven Diagnostics: IAC Counts

The IAC counts over 30 to maintain engine idle rpm indicate a problem. The most likely is carbon buildup on the throttle plate. 

Before cleaning throttle: 

After cleaning throttle:

Kenny@ggauto.repair

OBD II Modes: Mode 1 ($01) Display Current Data

 OBDII is a set of standards and practices used to fine tune emission programs across vehicle makes and models. It isn't a diagnostic system, it is an emission program. Knowing how OBDII is set up though can often be useful when you actually are doing vehicle diagnostics. There are 10 modes to OBDII. Generic or Global OBDII Mode 1 is there to display current data. Key to know here is that Global Mode 1 data is the actual sensor data as seen by the computer. If you are in OEM datastream, or Enhanced OBDII datastream you may not be seeing the actual data. In those modes, sometimes signals are substituted by default. Not all scan tools (or code readers) can read data and not all can read the various types of data. OBDII Mode 1 is limited to emission related data, yet it is *actual* emission related data. 

Remember that Global OBDII Mode 1 is actual data. 

Enhanced OBDII or OEM data can have substituted or default sensor data. Just something to be aware of when chasing car problems. 

Kenny@ggauto.repair