Read this entire document including the notes & comments at the bottom before attempting this procedure.
In order to successfully pass a State Emission Inspection in many states a series of tests conducted by the Motronic Ignition Computer (ECU) internal to a 993 must be completed and result in a PASS status for all the tests. The results of these tests are referred to as the Readiness States. They can be in a PASS, FAIL or NOT-READY state. The tests are made while the car is driven and each driving sequence for testing purposes is referred to as a Drive Cycle. The below procedure is designed to set all the Readiness States once any repairs are made and/or a reset event such as a battery disconnect or a reset using an On-Board Diagnostic Code (OBDC) reader has taken place.
This procedure is based on the published Porsche OBD-II Test drive document. It is intended to make the process simpler to complete successfully on a DIY basis.
Why success at the processes' completion seems somewhat variable for some:
The official Porsche document used to specify running conditions for the Readiness Tests specifies engine speed under specific engine loads for certain tests. This DIY procedure uses engine speed in combination with road speed & gearing as a proxy for engine load. This can result in a little bit of a hit or miss on meeting test conditions required on a single test drive cycle. This is most likely, for some, why completing the test drive and getting across the board PASS results takes more than one drive cycle to complete. 1996 and some early manufactured 1997 OBD-II cars require that all tests to be completed in a single engine running event contributing to the perception of offering additional difficulty completeing the Readiness test sequence.
This document includes consolidated information gleaned from personal experience, several public domain sources including Porsche enthusiast technical forums and Porsche published documents. The procedure described below is used successfully to set the Readiness statuses for many 993 owners, but this is not guaranteed for the above reasons.
 |
| Autel AL 519 Readiness Screen |
- Fuel Tank Ventilation
- Secondary Air Injection
- Oxygen Sensors
- Oxygen Sensor Heating
During the drive cycle, it helps to have a generic OBD-II reader such as the inexpensive Autel AL519 to see what progress you have made by reading out test statuses as "NOT READY", "PASS" or "FAIL" as you complete the process**. Not all generic OBD readers can see the readiness test status information.
**For MY 1996 and some early MY 1997 cars the ECU will only report to the reader statuses once all the tests are complete in a single drive cycle. For later MY 1997 forward cars each readiness status will report to the reader progressivly as each test is passed or fails.
The Drive Cycle:
1) Start the engine from dead cold, let idle for approx. 2 min, 10 secs.2) Accelerate to 20-30 MPH, in the 1600 to 2800 rpm range, (2nd or 3d Gear*), maintaining a steady speed for approx 3 min, 15 secs.(Tests Secondary Air Injection (SAI))
3) Accelerate to 40-60 MPH, do not exceed 60 mph in the 1600 to 2800 rpm range, (5th or 6th Gear*), maintaining a steady speed for approx 15 mins.(Tests Adaption Ranges II, Oxygen Sensor efficiency & Ageing-Heating)
4) Continue at 40-60 MPH, do not exceed 60 mph in the 1600 to 2100 rpm range, (5th or 6th Gear*), maintaining a steady speed for approx 1 min.(Tests Oxygen Sensor efficiency)
5) Decelerate and come to a stop and idle in neutral for 5 mins. for the six-speed cars and in Drive for Tiptronic cars(Tests Oxygen Sensor Period Length)
6) Check the statuses with an OBD reader to see if all have moved to a "PASS" status. If so your car is ready for state emission testing.(Tests Adaption range I & Tank Venting)
Notes:
For the 1996 and some early 1997 Model Year cars:- An initial cold start followed by two complete Drive Cycles without an engine shutdown between is required at a minimum to complete all the tests.
- After the second drive cycle, do not shut the engine off, use an OBDC reader to check to see if all the statuses have moved from NOT READY to PASS and/or FAIL. If not repeat the Drive Cycle without turning the engine off.
- If you see a "FAIL" result for one or more of the tests once the drive cycle(s) is complete, address the failed condition, reset the codes to NOT READY with your reader, and try again.
- If all the drive cycle tests are not completed before the engine is shut down, all the completed cycle status flags for that trip will revert to NOT READY. Early OBD-II 993s set monitors based on tests conducted in a single continuous engine running event including one or more Drive Cycles.
- These cars do not report out to the OBDC Reader individual Readiness statuses as individual test requirements are met, just all the results once all the test requirements have been completed after a series of Drive Cycles.
- There may need to be an extended, overnight cool-down period and then a new drive cycle sequence attempt conducted from an initial dead-cold engine if the Secondary Air Injection (SAI) test has not been completed at the beginning of the initial drive cycle in the sequence. This can arise when one clears the codes, causing a readiness reset via an OBDC Reader or a battery disconnect where the drive sequence is begun with a previously run engine that is not dead-cold.
- As each element of the test moves to a "PASS" or "FAIL" state, it will not revert to "NOT READY" until a reset event such as a reset using the OBDC Reader or the disconnection of the battery.
- If you see a "FAIL" result discontinue the Drive Cycle, address the failed condition, reset the codes, and try again. The reason is that there is no point in going any further as a system reset will be required and the test run will need to be repeated anyway to clear the "FAIL" and some tests may only run sequentially if a previous test related to it has moved to "PASS"
- Once the drive cycle is completed and one or more of the statuses is "NOT READY" and none have moved to "FAIL" do not reset the statuses with your code reader, just run through all the drive cycle steps again to pick up the additional "PASS" statuses needed.
- One can leave the Altel reader attached during the drive and check as each individual status flips to "PASS" or "FAIL" if one likes.
- The statuses are set individually over time as the vehicle is driven unrelated to the number of trips with engine shut-downs between.
- There may need to be an extended, overnight cool-down period and then a second drive cycle conducted if the Secondary Air Injection (SAI) status has not moved to "PASS" at the initial cold start at the beginning of the drive cycle. This can arise when one clears the codes, causing a readiness reset via an OBDC Reader or a battery disconnect where the drive sequence is begun with a previously run engine that is not dead-cold.
- The best result in getting all the statuses to change to a "PASS" is by being easy on the throttle with light accelerations when required.
- One source from the Pelican Parts discussion board in 2009, stated backing up with the car before or during testing or using cruise control will cause a problem with running the drive cycle. I have not been able to verify this. But by prepositioning your car the night before so no backing up is required in the morning the engine will be dead cold to test the SAI system and eliminates the need to put the car in reverse before the test run.
- After using this document any feedback to improve its clarity, accuracy, functionality, or reliability is greatly appreciated and can be added in the reply section below or by emailing me at Andrew.hess@differentlight.biz
- For reference here is the original factory OBD-II Drive cycle document.
kavocat
ReplyDeleteA Rennlist Member's comment
Thank you Andy for the consolidated notes.
I have read similar notes on the drive cycle from various places on the internet, and was frustrated by the rigid and precise times (many, like Andy’s consolidated notes, say “2 minutes and 10 seconds” and “3 minutes and 15 seconds”). Others claim that any stops during the drive cycle will cause it to fail.
My experiences have been different. My car had all red flags when I bought it (due to the battery being disconnected). I woke the following morning and started the car in my driveway. I let it idle for about 10 minutes (while I made my coffee) and then backed out and started to drive. I kept the speed under 30 mph and headed toward the freeway. It took about 10 minutes to get to the freeway, including five stops for traffic lights and stop signs. I then got on the freeway and drove at a steady 55-60 mph for 11 miles. I exited the freeway, parked in shopping center, and let the car idle for a few minutes. I checked the scanner and everything was green.
I recently reset a CEL, and, naturally, all flags were red. I did the above procedure again and it did not work – all the flags were still red. I tried again the following morning - same procedure as above - and the second time all the flags turned green.
Based on my experiences, I think the important part is to follow the recommended sequence, but not to worry about the precise and rigid times. It may take one drive, or it may take two. YMMV.
My car is 1997 C4S.