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Nissan System ReadinessPosted 11/24/2003By Paul Kujawa
The System Readiness Test (SRT) is used to support enhanced emissions inspections on vehicles equipped with on-board diagnostics (OBD) II. As you may know, the engine control module (ECM) performs functional tests on a variety of systems, with some of the more critical systems involved in controlling vehicle emissions being selected to be part of the SRT. The SRT involves the ECM's self-diagnosis system performing an inspection sequence on a given system, and then displaying through a scanner whether that system has been tested and passed the test. A system that has been tested and passed the test is displayed on the scanner as "complete." A system that has not been tested, or has not passed the test, is displayed on the scanner as "incomplete." Some states require that all SRTs be complete and that no diagnostic trouble codes are present for the vehicle to pass the emissions test. Systems commonly selected to be part of the SRT are catalytic converter operation, oxygen (O2) sensor operation, O2 sensor heater operation, EGR system operation and evaporative emission system operation. On Nissan vehicles, the ECM will perform a functional test of a given system once during each trip, as long as specific vehicle operating conditions are met during that trip. Once the functional test has been completed on a system, the ECM will not perform that test again until the key has been turned off, the engine restarted, the vehicle is driven and operating conditions are once again met. After two trips of successfully testing a system, the SRT will be displayed on the scanner as complete for that system. It is important to note that if the ECM self-diagnosis memory is cleared, the SRT items will be returned to "incomplete" status. It's often difficult to meet all of the vehicle operating conditions that are required by the ECM for the ECM to perform the functional test for a given system. This results in an "incomplete" next to a given system and a failed emissions test. To help meet the operating conditions required by the ECM, a driving pattern was designed that provides information such as engine temperature, engine rpm, vehicle speed, transmission gear position and base fuel schedule. The driving pattern is usually supplied in the factory service manual for a particular vehicle, but the pattern is typically a general driving pattern. Due to difficulty in completing system readiness testing on many 1996 and 1997 Nissan and Infiniti vehicles, Nissan Motor Corp. released technical service bulletins (Infiniti: No. ITB98-011c and Nissan: No. NTB98-018c) containing comprehensive road test driving patterns to enable the ECM to complete the SRT. Note: These service bulletins have specific individual driving patterns for each of the models Nissan builds and can have different driving patterns within a given model with variables such as Federal or California emissions, manual or automatic transmission and even ECM part number. If a vehicle comes in for repair due to an incomplete SRT, always check SRT status prior to servicing the vehicle to verify the SRT is still incomplete in case a normal driving pattern had been achieved and the SRT completed since the emissions test indicated an "incomplete" status. If the SRT status is still incomplete:
When you are trying to complete the SRT, the most important thing is to maintain the correct base fuel (B/Fuel) schedule as indicated on the drive pattern. B/Fuel schedule is an indication of engine load and is shown as the injector milliseconds that should be maintained during the drive cycle. Vehicle speed should be allowed to vary as necessary to maintain the correct B/Fuel schedule during cruise portions of the drive pattern as indicated. Also, when required B/Fuel schedule values are high, it can be easier to maintain the correct B/Fuel schedule by driving up a slight hill in the recommended gear range. Going down slight inclines can make it easier to maintain lower B/Fuel schedule values. A/C "on" will increase B/Fuel schedule. A/C "off" will lower B/Fuel schedule as well, to help try to maintain the correct B/Fuel schedule needed to complete the SRT. The SRT can also be helpful in confirming a repair if a diagnostic trouble code had been set that is related to a system covered in the SRT. After completing the repairs and clearing the code, the vehicle can be driven using the correct drive pattern. If a scanner shows the SRT to be "complete" after the drive pattern has been completed, the repair was likely successful.
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Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
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