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Tachometer Inoperative

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1999 Oldsmobile Bravada, 1999 GMC Sonoma, 1999 GMC Jimmy, 1999 GMC Envoy, and 1999 Chevrolet S10 Pickup. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform INSTRUMENT PANEL CLUSTER (IPC) SYSTEM CHECK  under SYSTEM TESTS. If entire IPC is inoperative, go to INSTRUMENT PANEL CLUSTER (IPC) INOPERATIVE  . If just tachometer is inoperative, go to next step.
  2. Start and idle engine. Observe tachometer. If an engine speed is indicated at idle, check for intermittent in wiring or connections. See WIRING DIAGRAMS  . If an engine speed is not indicated at idle, go to next step.
  3. Turn ignition off. Disconnect 16-pin engine harness-to-body harness connector C101. See COMPONENT LOCATIONS  . Turn ignition on. Using DVOM connected to ground, measure voltage at female side of 16-pin connector C101 terminal "A" (White wire). If more than 9.5 volts exists, go to step 7). If 9.5 volts or less exists, go to next step.
  4. Turn ignition off. Disconnect IPC connector. Remove instrument cluster as necessary for access to IPC connector. See INSTRUMENT PANEL CLUSTER (IPC)  under REMOVAL & INSTALLATION. Remove IPC connector comb. Using DVOM, check continuity of White wire (tachometer circuit) between 16-pin connector C101 terminal "A" and IPC connector terminal A3. See WIRING DIAGRAMS  . If continuity exists, go to next step. If continuity does not exist, go to step 9).
  5. Check continuity between ground and IPC connector terminal A3 (White wire). If continuity exists, go to step 10). If continuity does not exist, go to next step.
  6. Check for poor connection at IPC connector. Repair as necessary and retest operation. If IPC connection is okay, go to step 15).
  7. Turn ignition off. Disconnect Vehicle Control Module/Powertrain Control Module (VCM/PCM) Black connector (2.2L) or Red connector (4.3L). See COMPONENT LOCATIONS  . Using DVOM, check continuity of White wire (tachometer circuit) between 16-pin connector C101 terminal "A" and VCM/PCM Black connector terminal No. 10 (2.2L) or Red connector terminal No. 20 (4.3L). If continuity exists, go to next step. If continuity does not exist, go to step 11).
  8. Connect DVOM between ground and VCM/PCM Black connector terminal No. 10 (2.2L) or Red connector terminal No. 20 (4.3L). If continuity exists, go to step 12). If continuity does not exist, go to step 13).
  9. Repair open in White wire (tachometer circuit) between 16-pin connector C101 terminal "A" and IPC connector terminal A3. Retest operation.
  10. Repair short to ground in White wire (tachometer circuit) between 16-pin connector C101 terminal "A" and IPC connector terminal A3. Retest operation.
  11. Repair open in White wire (tachometer circuit) between 16-pin connector C101 terminal "A" and VCM/PCM Black connector terminal No. 10 (2.2L) or Red connector terminal No. 20 (4.3L). Retest operation.
  12. Repair short to ground in White wire (tachometer circuit) between 16-pin connector C101 terminal "A" and VCM/PCM Black connector terminal No. 10 (2.2L) or Red connector terminal No. 20 (4.3L). Retest operation.
  13. Check for poor connection at VCM/PCM Black connector terminal No. 10 (2.2L) or Red connector terminal No. 20 (4.3L). Repair as necessary and retest operation. If VCM/PCM connection is okay, go to next step.
  14. Replace and reprogram VCM/PCM. Go to GENERAL MOTORS (TRUCKS & VANS) in COMPUTER RELEARN PROCEDURES in GENERAL INFORMATION.
  15. Replace IPC. See INSTRUMENT PANEL CLUSTER (IPC)  under REMOVAL & INSTALLATION. Retest operation.
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