Clearing Trouble Codes

The following procedures are provided for use with a Rotunda New Generation STAR (NGS) Tester. For procedures using a generic scan tool, refer to Powertrain Management/Computers and Control Systems.

Special Test Modes

- Diagnostic Test Modes
- PCM Reset Mode

Diagnostic Test Mode

The diagnostic test mode (DTM) aids in servicing output actuators associated with the OBD II system. It allows the technician to energize and de-energize most of the system output actuators on command.

Performing Diagnostic Test Mode

NOTE: You must enter DTM with ignition switch in RUN and the engine off.

- Perform visual inspection and vehicle preparation as required.
- Select "Vehicle and Engine Selection" menu.
- Select year, engine, model with the appropriate qualifier if needed (for example, transmission or 49 state/Cal).
- Select "Diagnostic Data Link" menu.
- Select "Diagnostic Test Mode" menu.
- Enter "Active Tests".
- Enter "Output Control".
- Follow operating instructions from the NGS menu screen.

PCM Reset Mode

The PCM reset mode permits the NGS to command the PCM to clear all DTCs. When resetting the PCM, a DTC P1000 will be set in the PCM until all OBD II system or components have been monitored during OBD II Drive Cycle.

A PCM reset:

- Clears the DTCs
- Clears the freeze frame data
- Clears the oxygen sensor test data
- Resets the status of the OBD II system monitors
- Sets the DTCP1OOO

Performing PCM Reset

- Perform visual inspection and vehicle preparation as required.
- Select "Vehicle and Engine Selection" menu.
- Select year, engine, model with the appropriate qualifier if needed, for example, transmission or 49 state/Cal.
- Select "Generic OBD II Functions" menu.
- Select "Clearing ALL Codes".
- Follow operating instructions from the NGS menu screen.
- Perform OBD II Drive Cycle-Clear DTC P1000.

Clearing DTC P1000

In some localities it may become a legal requirement to pass an Inspection/Maintenance (I/M) test of the OBD II System. If the vehicle OBD II system or its battery has just been serviced, the PCM system is reset to a "not ready for I/M testing" condition. To prepare the vehicle for this test and to clear the DTC P1000, the OBD II Drive Cycle must be performed.

OBD II Drive Cycle

NOTE: The following steps must be run in the order shown. If steps 2, 3 or 4 are interrupted, repeat the step before proceeding. Any safe driving mode is acceptable between steps.

Always drive vehicle in a safe manner according to traffic conditions and obey all traffic laws.

1. Start engine and drive vehicle in typical city stop and go traffic for at least 10 minutes after engine has reached normal operating temperature.

2. Idle vehicle for at least 45 seconds, then accelerate at part throttle to about 72 km/h (45 mph).

3. Cruise and maintain a speed in the range of 48 to 64 km/h (30 to 40 mph) on a level road with throttle held steady for at least one minute.

4. Cruise and maintain a speed in the range of 64 to 105 km/h (40 to 65 mph) on a level road with throttle held steady for at least one minute and 20 seconds.

5. OBD II Drive Cycle has been completed.

Other NGS Features

Other diagnostic methods include the following:

- Parameter Identification (PID) Access Mode, used to monitor sensors and actuators
- Freeze Frame Data Access Mode, used to view emission related data values from specific PIDs
- Oxygen Sensor Monitor Mode, used to monitor the heated oxygen (HO2S) sensor

Transmission Drive Cycle Test

After performing the Quick Test, use the Transmission Drive Cycle Test for checking transmission continuous codes.

NOTE: The Transmission Drive Cycle Test must be followed exactly. A malfunction must occur four times consecutively for DTCs P0781, P0782, P0783, P1731, P1732, P1733 to be set, and five times consecutively for continuous DTC P0741.

1. Record and then erase Quick Test DTCs.

2. Warm engine to normal operating temperature.

3. Make sure transmission fluid level is correct.

4. With transmission In OVERDRIVE, moderately accelerate from stop to 80 km/h (50 mph). This allows the transmission to shift into fourth gear. Hold speed and throttle open steady for a minimum of 15 seconds.

5. With transmission in OVERDRIVE, press TCS (TCIL should illuminate) and moderately accelerate from stop to 64 km/h (40 mph). This allows the transmission to shift into third gear. Hold speed and throttle open steady for a minimum of 15 seconds (30 seconds above 4000 ft).

6. Press TCS (TCIL should turn off) and accelerate from 64km/h (40mph) to 80km/h (50mph). This allows transmission to shift into fourth gear. Hold speed and throttle position steady for a minimum of 15 seconds.

7. With transmission in fourth gear and maintaining steady speed and throttle opening, lightly apply and release brake to operate stoplamps. Then hold speed and throttle steady for a minimum of five seconds.

8. Brake to a stop and remain stopped for a minimum of 20 seconds.

9. Repeat Steps 4 through 8 at least five times.

10. Perform Quick Test and record continuous DTCs.