DTC P0121: Throttle Position (TP) Circuit Range/Performance Problem (Esteem 1.6L & Swift)
NOTE:
On Esteem 1.6L and Swift, if DTC P1450 or P1451 are set, diagnose that DTC first.
- 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 C22 terminal No. 6 (Gray wire on Esteem 1.6L, or Light Green/White wire on Swift), or between ground and PCM 20-pin harness connector terminal No. 25 (Gray wire on Esteem 1.8L).
- 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 Esteem 1.8L Closed .35-.65 Open 3.5-4.5 All Others Closed 0.2-1.0 Open 2.8-4.8 - On Esteem 1.6L and Swift, go to next step. On Esteem 1.8L, warm engine to normal operating temperature. Ensure fast idle cam and cam follower lever are not in contact with each other. Loosen TP sensor screws. If using scan tool, turn ignition off and connect scan tool to DLC. If scan tool is unavailable, backprobe digital voltmeter between PCM 20-pin connector terminal No. 25 (Gray wire) and ground. If voltage is to specification, go to next step. If voltage is not to specification, turn TP sensor clockwise or counterclockwise until correct voltage is to specification. See TP SENSOR VOLTAGE table.
- 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.TP SENSOR RESISTANCE
Between Terminals No. Ohms 1.8L Esteem 1 & 3 4000-6000 1 & 2 (1) 100-6500 All Others 1 & 2 2.5-6.0 1 & 3 (1) 100-20,000 (1) Varies with throttle position.