On Board Diagnostic Codes (OBDC) use notes

What On-Board Diagnostic reader will work with a 993 & 964?  - By US law all cars manufactured in 1996 forward have to produce generic codes that are compatible with a generic reader that covers basic engine systems that influence emissions this is also true for the 993. Also, some generic readers can reach back to the 964 cars and read their codes as well. 

Reading real-time running data from the various sensors, the ability to turn devices on and off manually, and reading codes from the non-emissions related 993 modules/systems, ABS. HVAC etc. is something a very few reasonably priced readers can do. 

Non-emission-related modules include  HVAC, ABS, Supplemental Restraint System (air-bag), and Transmission (for Titronoc equipped cars). A commercial product that can read all the modules, display and record running data, and actuate certain functions, for example, the supplemental air injection blower, is  Durametric Enthusiast Cable & software, Also there is the  Rennlist Scantool Windows software freeware used with a generic OBD cable such as available through Tore at BergvillFX.com. that has some advanced features although I have been unable to find a published feature list or instruction manual for this software. Beyond these don't expect any of the less than $500 readers to read all the 993's modules' codes no matter what the box says.

Here are OBDC readers the can access all the modules in a 964/993:

• The Bosch Porsche "hammer" (KTS 301) or the Porsche  PST2 or PIWIS v1 or v2;
• Freeware Rennlist Scantool Windows software used with the T-OBD serial port adapter;
• The commercial product, Durametric Windows software with their proprietary serial cable
• Jennisken's OBD UDT/PDT999 diagnostic tool

What are Readiness Tests/Codes/Flags:

For ALL OBD-II cars, 1996 forward, These cars have something called Readiness Testing it is a series of EPA mandated specific timed tests the engine management does during specific running conditions and at cold start. Whenever the battery on the car is disconnected all the readiness codes, sometimes referred to as flags,  are reset to "NOT READY" as the system cycles through redoing tests. 

If all your need is to read emission codes or OBD-II readiness statuses to prepare for state emission testing a good inexpensive generic reader is all you will need such as the Autel AL519 handheld reader.

Using your OBD reader with a 993 /964: 

Your car has one of two styles of OBD ports, one is; 

• The somewhat square style pictured at the top of this page is located in the driver footwell on the sidewall of the center console. All OBDII cars and late OBD1 cars have this style socket. The other is; 
• The older OBDI round-style socket requires an adapter to use with the square plug that is standard on most readers. The round adapter can be purchased here. Early 1995 model-year 993 cars have a round port cover plate on the passenger footwell outer wall, not on the center console side.

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Here is a page with information on Pre-MY 1996 OBD-I Diagnostics

If your 1996 or newer OBDII car has the immobilizer function both the ignition switch needs to be in the ON position and the immobilizer disengaged for the reader to make contact with the various modules in the car. Doing this involves locking and then unlocking the door using the electronic fob to enable the ECU before inserting the key in the ignition or attaching the reader. Also, the wired connection is through a serial cable so if your reader is a cable used in conjunction with a laptop it may have a more successful time establishing communications (handshake) with the laptop powered by wall current vs running on battery power alone. Some readers may require more than one port plug-in attempt to successfully establish communications. I have had this issue with Durmetric using a laptop and their older OBD cable & software. 

By law in 1996 and so with a 1996 and forward 993 the OBD socket to plug the reader must be in the driver-side footwall. In the 993 it is behind a black plastic door on the carpeted side of the center console under the dash. On the earlier 964, the socket is under a round cover on the sidewall of the footwell. 

On-Board Diagnostic connections -  I have found that as a best practice if one experiences a fault code related to an electronic sensor such as an oxygen sensor, wheel rotation sensor or an electronic device such as the Idle Control Valve it is best to clean the electrical plug and socket to the device before assuming it is a failed component as a dirty connector is simply a fact of life on a 25+-year-old car. Also if your OBDC Reader is acting strangely it is not a bad idea to clean the diagnostic port on your car and the plug supplied with your reader.

OBD Code Ignition Faults - On a 993 if the ignition wires are bad, one of the rotors or caps are bad, the plugs are fouled or a rotor cap is loose the light will likely be on with a misfire OBD Code present.

Getting meaningful OBD Code information from your reader -  On our cars, many of the fault codes are the result of indirect information received from the oxygen and other sensors that are analyzed by the Motronic Electronic Control Unit. For this reason, the proper operation of the sensors is paramount in allowing your reader to give you good information. For example, if you have ignition or emission codes that relate to data the oxygen sensors provided it is advisable to replace any suspect oxygen sensors then clear the codes and see if any return before coming to any conclusions as to the root cause of the Diagnostic Code.

Here is the master list of codes for 1996 forward OBD-II cars and definitions for each code.

I use Durametric's Enthusiast cable for my OBD-II 1996 Carrera in combination with a laptop computer and their software. I understand it doesn't include low-level coding access to the modules as the professional product does, a feature I do not miss as I don't think there are any direct access codes that can be changed without replacing a chip on a 1996 993.

Here is the functionality it provides for the 993:

Here is the functionality it provides for the 964:

In the USA OBD-I cars are the model year 1995 and earlier cars. The system uses one oxygen sensor that measures the entire effectiveness of the emission system and so does not test the operation of the emission Auxillary Air Injector System separately, a system that only influences emissions for a few seconds at startup. For this reason, these cars generally pass state emission inspections even if the air injector system or any of its components are faulty as long as the Check Engine Light is not illuminated.

The USA OBD-II cars are the model year 1996 and forward years. They use four oxygen sensors and therefore can measure both the effectiveness of the catalytic converter AND separately the Auxiliary Air Injection System. This is why an inoperative air injection system on these cars will cause a diagnostic fault and a check engine light that will cause the vehicle to fail a state emissions inspection. This will be the case even in states that do inspections but do not carry out tailpipe testing. If your car is an OBD-II vehicle here is a page that discusses mitigations to faults related to the Auxillary Air Injector System.

I  have found that at times Durametric provides erroneous information.

 Things such as listing fault codes that do not exist in the Porsche OBDC catalog of codes or even codes that seem to not clear properly when reset. To minimize this issue always check the Durametric website and verify you are using the latest version of their software. Be sure to uninstall the old version before installing the new one to avoid functional issues. 

In my case, I purchased a 2nd basic function generic handheld Autel AL519 reader just for reading ignition module codes that I use from time to time to validate what I am seeing from the Durametric software. As a plus, the Autel reader also displays the individual status for all five non-continuous readiness codes for all 1996 OBD-II and forward model year cars.

Early OBDC-II cars manufactured in 1996,  the first year of OBDC-II compliance only report out to an OBDC Reader when all the tests are completed in a single continuous engine running a  test drive cycle. If all tests are not completed during this running all the codes revert to "NOT READY" when the engine is turned off and the testing cycle will start over the next time the engine is started. Later model-year cars will store and report individual test results as they are completed and resume testing for incomplete tests upon an engine restart. This is why some may find that it takes longer or seems more difficult to set the readiness flags on 1996 and some early build 1997 model year cars.

Here is a page that discusses how to conduct a drive cycle to set all the Readiness Codes.

Here is a page discussing how to prepare for a State emissions test with a 993

  Basic OBDII Readiness Codes Non-Continuous Monitoring Tests*:

(*see descriptive note below)

     - Three-Way Catalytic Converter (TWC) Efficiency
     - Fuel Tank Ventilation (EVAP)
     - Secondary Air Injection (SAI)
     - Oxygen Sensors
     - Oxygen Sensor Heating

   Basic OBDII Readiness Codes Continuous Monitoring Tests:

(Monitors these functions every time the engine is running)

     - Fuel System (TRIM)

     - Electronic Control Module (ECM) Diagnostic Trouble Code faults (DTC)
     - Cylinder Misfire - A fault is thrown if too many misfires are detected.

*Non-continuous monitors execute only under specific conditions and driving behavior. The vehicle operating conditions required for the non-continuous monitors to execute are referred to as the enabling criteria. Some monitors require the vehicle to follow a prescribed drive cycle routine as part of the enabling criteria. 

Some non-continuous monitors require two drive cycles to complete testing.  This is due to the need for a cold start to verify the operation of the Supplemental Air Injection (SAI) system or variables such as speed, engine and ambient temperatures, load, fuel level must be met for the monitor to complete all the tests. Here is a page on how to conduct the required drive cycles.

Once the tests are complete the OBD-II Readiness statuses within the ECU move from "NOT READY" to "PASS" or "FAIL". 

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#OBD #OBDC #OBDC-II #On board diagnostic