Testing Procedure
WARNING: This page is about a different car, the 2003 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Many aftermarket OBD II scan tools are limited in diagnostic capabilities, using the SAE Recommended Practice J1978, which defined the basic requirements of an OBD II scan tool. Most manufacturers service manuals describe repair procedures that require scan tool diagnostic capabilities beyond the ability of the aftermarket OBD II scan tools using only SAE Recommended Practice J1978. To perform these diagnostic test functions without having each manufacturers hand-held tester requires enhanced OBD II scan tools using the basic requirements and a standard set of diagnostic test modes, the SAE Recommended Practice J1979, which defines the test modes used by both the vehicle and the OBD II scan tool to access vehicle information and functions.
To perform test procedures outlined in most manufacturers service manuals, an OBD II scan tool compliant with SAE J1979 is required to contain the following test modes:
- MODE 1 - Display current diagnostic data parameters.
- MODE 2 - Display freeze frame data captured by the vehicle along with DTC(s).
- MODE 3 - Display emission-related powertrain DTC(s).
- MODE 4 - RESET ECM/PCM: Clear DTC(s), freeze frame data, and any other diagnostic information from the on-board controller's memory.
- MODE 5 - Displays results of Oxygen Sensor monitoring tests.
- MODE 6 - Displays results of on-board monitoring tests for non-continuously monitored systems.
- MODE 7 - Displays results of on-board monitoring tests for continuously monitored systems and status of vehicles on-board readiness code tests. In addition to these standard set of diagnostic test modes, the SAE Recommended Practice J1979, some scan tool manufacturers have provided even more enhancements, such as road test support through capture of sequences of data parameters (SNAP SHOT MODE), and user-selectable parameter list (DATA LIST) allowing user to trade off update (refresh) rate for amount of data.
- MODE 8 - Request control of on-board system, test or component.
- MODE 9 - Displays vehicle information; VIN and calibration numbers, etc.
To ensure correct diagnosis and repair, testing should be done in the following sequence:
- Record Customer Complaint
Ensure all customer complaints or observations are recorded. Test drive vehicle with customer when necessary for malfunction verification. - Retrieve Diagnostic Trouble Codes
Using Toyota hand-held tester or scan tool, retrieve Diagnostic Trouble Codes (DTC) from Engine Control Module (ECM) and record any freeze frame data (if applicable). See RETRIEVING DIAGNOSTIC TROUBLE CODES . - Clear Diagnostic Trouble Codes
Using Toyota hand-held tester or scan tool, clear DTCs and freeze frame data from ECM. See CLEARING DIAGNOSTIC TROUBLE CODES . - Visual Inspection
Inspect all electrical connectors and wiring for suspected circuit or component. Ensure all connections are clean and tight. - Confirm Symptoms & Diagnostic Trouble Codes
Perform road test. Determine if original symptoms still exist. Using scan tool or Toyota hand-held tester, retrieve DTCs from ECM. See RETRIEVING DIAGNOSTIC TROUBLE CODES . - Diagnose & Repair Diagnostic Trouble Codes
Perform appropriate DTC test listed under DIAGNOSTIC TESTS as necessary. For DTC descriptions, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are present and a no start condition exists, proceed to BASIC DIAGNOSTIC PROCEDURES - V6 & V8 article. If no DTCs are present and a driveability condition exists, proceed to TROUBLESHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.). - Verification Procedure
After repairs have been completed, clear all DTCs from ECM. See CLEARING DIAGNOSTIC TROUBLE CODES . Perform road test. Ensure no DTCs exist and all symptoms and/or complaints have been repaired.