OBD Diagnostic Monitors (Drive Cycles)

NOTE: When performing diagnostics on a vehicle technicians should be aware that erroneous codes may be introduced by their actions. In order to ensure correct diagnosis, all codes should be noted, before commencing diagnosis, so that induced codes can be identified on completion and safety cleared without further work.

Introduction
Most of the frequent diagnostic tests involving sensors and actuators will run within approximately 20 seconds of starting the engine. The other less frequent diagnostics are timed such that they occur and complete within the Federal Test Pipe (FTP) drive cycle when conditions are appropriate to providing a correct outcome.

For the purposes of the service technician a more expedient method of generating a trip is described below. This should ensure that all diagnostic routines are exercised. Any fault information regarding any of the tests will be held in the GEMS system fault messages received parameters. It must be remembered that the GEMS system operates a two trip logic convention as allowed by CARB; i.e. two defined trips are required to switch on the MIL unless the faults compromise functionality of the whole system, causing the MIL to switch on immediately.

Service Drive Cycle
The Service Drive Cycle procedure confirms the presence of a fault(s), successful repair and clears reported DTC(s) from the ECM. It is not necessary to test the whole vehicle system through its complete range of performance for each DTC. It is recommended that the Drive Cycle is included in the post repair road test.

1. Allow the car to "SOAK" at room temperature until the coolant temperature reaches 60 °.
2. Start engine.
3. Idle for approximately 8 minutes; diagnostics such as a misfire, sensors and actuators will run and produce an outcome. An additional test requiring the engine to run for 15 minutes is present, thus a long idle period is the most appropriate method consuming time without excessive miles being clocked.
4. Accelerate in drive (maximum gear 3rd engine speed 2000 rpm, wide open throttle), up an incline to maintain a high load for approximately 10 seconds, this will test the Neutral Drive switch and Road Speed diagnostics.
5. Drive as normal, while driving, change through the gears briskly such that 40 gear changes are requested. This further tests the Neutral Drive Switch.

NOTE: Required gear changes must be between gears, not between Neutral and Drive.

6. Accelerate in drive to a target road speed in the range of 35-45mph, then cruise at target speed preferably in a flat surface to achieve a steady load. Attempt to maintain the speed for a duration of approximately 3 minutes. This allows adaptations and the Catalyst monitoring routine within the system to take place.
7. Come to idle and park.
8. Rev the engine to 1500/2000 rpm for a duration of approximately one minute.
9. Wait at idle for a period of 2 minutes.
1O. Interrogate Generic Scan Tool and establish faults, if any.
11. Switch off engine.