Preparing for Passing an Emissions Tail Pipe Test with a 993:

I regularly read postings like this by folks who were able to clear a failed tailpipe inspection on their 993 by doing this:

" Took my '95 993 (148k miles) [an OBD-I car] for typical California smog test. Never had a failure. Except this time! High HC values [of 47 Parts Per Million - (PPM) Max. allowed 35PPM]."

Added a bottle of Swepco 503 fuel adder, filled the tank, and drove the snot out of the 993 over the weekend (240 miles, up and down the coast. High rev's and aggressive (but safe!) driving). Came back, re-tested, and blew all the numbers out of the water [well within allotted maximums]! Passed with flying colors" "Bottom line, car needed a proper "Italian tune-up". I've been driving the car frequently, but going to Chick fil A with my kids does not cut it. Car needed a serious work-out. Lesson learned."

If you live in a state where tailpipe emissions testing is done here is what preparation is needed to pass the test without drama.

• Checking for the readiness of the emission reporting system to conduct an emissions test:

• For 1995 and earlier OBD-I cars if you have a Check Engine Light (CEL) illuminated do what is needed to clear the code, discussed below. A good inexpensive choice is to run the OBD Codes with a generic handheld Autel AL519 reader. For these early cars, it is usually something very simple like the replacement of the one oxygen sensor, an inexpensive part if purchased in BOSCH branded box from a general auto parts store and is easily replaced in your driveway. The how-to is on this page. The OBD code(s) given, in most cases, makes it specific as to what is needed to be done. Once the cause of the CEL is addressed clear the codes with the reader or by disconnecting the car battery if the CEL persists.

• For ALL OBD-II cars, 1996 forward, These cars have something called Readiness Testing which 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. 
   
  The issue is that unless specific driving conditions are met one or more of the tests remain incomplete and when the car goes in for emission inspection & testing it will fail the emission inspection. Also upon being reset any change in the engine's running condition that has resulted in it not functioning properly will report as a "FAIL" from the system on the related test. Seems simple enough except for the typical car owner it can take weeks or months for the car to have completed all the necessary driving cycles to set all the readiness code statuses to a "PASS" condition. Compounding this is disconnecting the battery is a common procedure during many routine service and repair activities.

Here is how to go about managing the readiness tests:

• First of all, when using an On-Board Diagnostic reader the ignition on the 993 must be on and the Immobilizer inactive on so-equipped cars for the reader to access the MOTRONIC ECU and retrieve the readiness codes. No need for the engine to be running to see the diagnostic information. 
• Run the OBD Codes if a CEL light is present or not using an OBD code reader such as an Autel AL519. check the individual readiness code states and for any "FAIL" statuses, the car will need to have any "FAIL" statuses addressed, the codes reset (cleared) via the reader's reset function or disconnecting the car battery, then run through the OBD-II Test Drive to set all the readiness code statuses from "NOT READY" to "PASS". 
• More on On-Board Diagnostics (OBD) and the readiness code status can be found here. 
• Actions Taken nine times out of ten to remedy a "FAIL" on 1996 forward OBD-II cars there is a problem with the Secondary Air Injection (SAI) System with a few ways to address it here.  Specifically, the air system's check valve is regularly the culprit and can be replaced.

• Change the oil

• If your caps and rotors on your distributors are more than three years old consider changing them this is especially important if you are encountering an occasional  OBD Code "Cylinder Misfire" with a CEL illuminated from time to time that, self-extinguishes.

• Drive the car until it is good and hot just before going in for emissions testing. A half-hour of spirited driving brings the temperature gauge up to its normal operating range. The definition of spirited driving is to run through the gears so in several instances the engine is run near or to redline during acceleration.

• Do not turn the engine off, with the hot engine drive directly to the inspection center to have your car's emissions tested. Do not turn off the engine at any point before the inspection while waiting in the inspection queue for your turn. Turning off and restarting the engine may introduce enough unspent fuel into the exhaust system to trigger a fail on the tailpipe emissions test.

If you found this page informative return to the main page and bookmark it for future 993-related servicing, repair, and upgrading guidance & information. If it saved you some aggravation or even some coin consider a donation through the button on the top left margin of this page.