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

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

1. Turn ignition on. Using a voltmeter, measure voltage (backprobe) between ground and PCM connector "B", terminal No. 6 (Light Green/White wire) with throttle closed (idle position), then fully open. Adjust TP sensor if voltage is not as specified. See TP SENSOR VOLTAGE table. See ADJUSTMENTS article for adjustment procedures. If TP sensor tests 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. See Fig 1 . Using an ohmmeter, measure resistance between specified TP sensor terminals. See TP SENSOR RESISTANCE  table. Replace TP sensor if resistance is not as specified. If resistance is as specified, check Light Green wire, Light Green/White wire or Light Green/Black 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 & 4	2.87-5.33
1 & 3	(1) 100-20,000
(1) Varies with throttle position.

Fig 1: Identifying TP Sensor Terminals

Courtesy of SUZUKI OF AMERICA CORP.