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DTC P0121: Throttle Position (TP) Circuit Range/Performance Problem

NOTE: If DTC P1450 or P1451 is set, diagnose that DTC first.
  1. Start engine and warm to operating temperature. Turn engine off and connect scan tool to Data Link Connector (DLC). If scan tool is not available, use DVOM to backprobe between ground and PCM 16-pin harness connector "B" terminal No. 6 (Gray wire on Esteem, or Light Green/White wire on Swift).
  2. Turn ignition on and observe TPS voltage with throttle closed (idle position), then fully open. Compare TPS voltage to specifications in TP SENSOR VOLTAGE  table. As throttle position is changed from closed to open, TP sensor voltage should rise smoothly. If TP sensor reading is erratic, go to next step. If TP sensor is okay, check PCM for poor connections. If connections are okay, replace PCM. Retest system.
    TP SENSOR VOLTAGE

    Throttle Position Volts
    Closed 0.2-1.0
    Open 2.8-4.8
  3. Turn ignition off. Disconnect TP sensor harness connector. Use DVOM to measure resistance between specified TP sensor terminals. See Fig 1 . See TP SENSOR RESISTANCE  table. If resistance is not as specified, replace TP sensor. If resistance is as specified, check wires between TP sensor and PCM for high resistance (Pink/Green, Green/Red or Gray wires on Esteem, Light Green/White, Light Green/Black or Light Green wire on Swift). Repair as necessary. If wires are okay, replace PCM. Retest system.
    Fig 1: Testing TP Sensor
    G98A12336Courtesy of SUZUKI OF AMERICA CORP.
    TP SENSOR RESISTANCE

    Between Terminals No. Ohms
    1 & 2 2.5-6.0
    1 & 3 (1) 100-20,000
    (1) Varies with throttle position.
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