Reading and Clearing Diagnostic Trouble Codes

When trying to verify a speed control system electronic malfunction, one of two methods may be used, the Diagnostic Readout Box (DRB) or a Voltmeter.

USING DIAGNOSTIC TOOL
1. Connect DRB Diagnostic Tool to six way diagnostic connector located at right hand side of steering column, then inspect for diagnostic trouble code 15, 34 or 77. Refer to Diagnostic Charts.
2. If DRB Diagnostic Tool displays "No Response," then go to test NS-6A and NS-6B. After performing test NS-6A and NS-6B perform verification test VER-1.
3. If no diagnostic trouble codes are displayed, then refer to tests SC-1A through SC-6A.
4. After performing all other diagnostic tests, perform verification test VER-2.
6. Follow tool manufacturers instructions for proper installation of the tool prior to testing speed control system. If no problems were found, replace engine controller.

USING VOLTMETER
If a DRB Diagnostic tool is not available, check for diagnostic trouble codes as follows:

1. Cycle ignition switch to On position three times. On third cycle, leave switch in On position.
2. Observe Check Engine indicator on instrument cluster. If a diagnostic trouble code is present, CHECK ENGINE indicator lamp will flash (blink) in a series which will show which diagnostic trouble code is the problem.
3. If no diagnostic trouble code, or if code 34 is observed, perform "Electrical Test At Servo", "Speed Control Switch Test" and "Powertrain Control Module Test".
4. If diagnostic trouble code 15 is present, test Vehicle Speed Sensor. Testing of Vehicle Speed Sensor requires the use of the DRB diagnostic tool.
5. If diagnostic trouble code 77 is present, refer to "Speed Control Relay Test".
6. Repair any problems found, then recheck for diagnostic trouble codes after repairs have been completed.
7. If no problems were found, replace powertrain control module.