LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Buick >> 1996 >> Roadmaster Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control Systems - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P1643 - Engine Speed Output Circuit >> Diagnostic Procedures
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
  2. With engine running, observe is vehicle tachometer is indicating engine RPM. If RPM is indicated, see DIAGNOSTIC AIDS. If RPM is not indicated, go to next step.
  3. Turn ignition off. Disconnect PCM connector C1. Install Signal Generator Tester (J 33431-B) to engine speed output circuit of PCM harness connector terminal C1 and ground. Turn ignition on. Turn tester on and set tester to generate a tachometer signal. If vehicle tachometer indicates an RPM reading, go to next step. If tachometer does not indicate an RPM reading, check tachometer circuit to instrument panel.
  4. Check for faulty PCM connections. Repair as necessary. After repairs, go to step 6). If connections are okay, go to next step.
  5. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  6. Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1643. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool did not indicate that this test ran and passed, repeat step 2).
  7. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
scientia non olet · About LEMON Manuals