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

NOTE: If DTC P1450 or P1451 is set, diagnose that DTC first.

1. Turn ignition on. Measure voltage (backprobe) between ground and PCM harness connector "B", terminal No. 6 (Gray wire) with throttle closed (idle position), then fully open. See TP SENSOR VOLTAGE  table. Adjust TP sensor if voltage is not as specified. See ADJUSTMENTS article for adjustment procedures. If voltage is as specified, go to next step.
   TP SENSOR VOLTAGE
   
   

   Throttle Position	Volts
   Closed	0.1-1.1
   Open	3.2-4.6

2. As throttle position is changed from closed to open, TP sensor voltage should rise steadily. 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.
3. Turn ignition off. Disconnect TP sensor harness connector. 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 Pink wire, Gray wire or Green/Red wire between TP sensor and PCM for high resistance. Repair as necessary. If wires are okay, replace PCM. Retest system.

TP SENSOR RESISTANCE

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

Fig 1: Testing TP Sensor

Courtesy of SUZUKI OF AMERICA CORP.