Variable Tumble Control System (VTCS) Vacuum Switch Inspection (Miata)

1. Disconnect vacuum hose and 2-pin harness connector from VTCS vacuum switch. Connect vacuum pump to port on VTCS vacuum switch and DVOM to VTCS connector terminals. Slowly apply vacuum to VTCS vacuum switch. See VTCS VACUUM SWITCH VACUUM APPLICATION  table. If VTCS vacuum switch is okay but PID value is out of specification, check for short or open circuit. Go to next step. If continuity is not as specified, replace VTCS vacuum switch.
2. Open Circuit Inspection
   
   Disconnect PCM harness connectors. Using DVOM, check for continuity in following circuits:
   • Power circuit (Orange wire) between VTCS vacuum switch harness connector terminal "A" and PCM 31-pin harness connector terminal No. 4J.
   • GND circuit (Black wire) between VTCS vacuum switch harness connector terminal "B" and ground through common connector.

   If continuity is present, go to next step. If continuity is not present, repair open circuit in suspect wire or replace wire harness. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, return vehicle to original condition.

3. Short Circuit Inspection
   
   Check for continuity to ground in Orange wire between VTCS vacuum switch harness connector terminal "A" and PCM 31-pin harness connector terminal No. 4J through common connector.

If continuity is present, repair short circuit to ground in Orange wire between VTCS vacuum switch harness connector terminal "A" and PCM 31-pin harness connector terminal No. 4J through common connector or replace wire harness.