LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Suzuki >> 1999 >> Grand Vitara JS, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0121: Throttle Position (TP) Sensor System Performance >> Diagnosis & Repair Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnosis & Repair Procedure

  1. Remove PCM cover, located below right side of instrument panel. Start engine and allow to reach normal operating temperature. Turn engine off. Connect DVOM (backprobe) between PCM 26-pin connector "B" terminals No. 12 (Red/Green wire) and No. 20 (Gray/Yellow wire). Turn ignition on. Measure voltage with throttle in closed and fully open positions. DVOM should display .35-.65 volts with throttle in closed position and 3.5-4.5 volts with throttle in fully open position. If voltage is as specified, go to next step. If voltage is not as specified, go to step  3 .
  2. Visually inspect for any obstructions or leaks in MAF sensor ducting. Repair as necessary. If air intake system checks okay, replace PCM. See REMOVAL, OVERHAUL & INSTALLATION article. Retest system.
  3. Turn ignition off. Ensure there is clearance between fast idle cam and follow lever. Disconnect TP sensor harness connector. Using ohmmeter, measure resistance between TP sensor terminals No. 1 and 3. See Fig 1 . Resistance should be 4-6 k/ohms. Connect ohmmeter between TP sensor terminals No. 2 and 3. Resistance should vary 0-4.6 k/ohms according to throttle opening. If resistance is as specified, go to next step. If resistance is not as specified, replace TP sensor. See REMOVAL, OVERHAUL & INSTALLATION article. Retest system.
  4. Using DVOM, measure voltage between ground and TP sensor harness connector terminal No. 3 Gray/Red wire). If 4.5-5.5 volts exists, go to next step. If 4.5-5.5 volts does not exist, check for open in Gray/Red wire. See WIRING DIAGRAMS article. Repair as necessary. If Gray/Red wire is okay, replace PCM. See REMOVAL, OVERHAUL & INSTALLATION article. Retest system.
  5. Using ohmmeter, check continuity between ground and TP sensor harness connector terminal No. 1 (Gray/Yellow wire). If continuity exists, go to next step. If continuity does not exist, check for open in Gray/Yellow wire. See WIRING DIAGRAMS article. Repair as necessary. If Gray/Yellow wire is okay, replace PCM. See REMOVAL, OVERHAUL & INSTALLATION article. Retest system.
  6. Connect DVOM (backprobe) between ground and PCM 26-pin connector "B" terminals No. 12 (Red/Green wire). Turn ignition on. Loosen TP sensor retaining screws. Rotate TP sensor to achieve .35-.65 volt with throttle closed. Tighten TP sensor retaining screws. Fully open throttle. TP sensor reading should be 3.5-4.5 volts. If TP sensor voltage is within specification after adjustment, retest system. If correct TP sensor voltage cannot be obtained during adjustment, replace PCM. See REMOVAL, OVERHAUL & INSTALLATION article. Retest system.
Fig 1: Identifying Throttle Position (TP) Sensor Terminals
G99E50777Courtesy of SUZUKI OF AMERICA CORP.
scientia non olet · About LEMON Manuals