P0121 - Throttle Position Sensor 1 Performance: Notes

Fig 1: Identifying Throttle Position Sensor Wiring Diagram

Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

Theory of Operation

The Electronic Throttle Control (ETC) system uses two Throttle Position Sensors (TPS) to monitor the throttle blade position. The Throttle Position Sensors 1 and 2 are located within the Throttle Body assembly. Each sensor has a 5-Volt reference circuit, a low reference circuit, and a signal circuit. Processors are also used to monitor the ETC system data. The processors are located within the Powertrain Control Module (PCM). Each signal circuit provides the processors with a signal voltage proportional to throttle blade movement. The processors share and monitor data to verify that the indicated TPS calculation is correct.

>>When Monitored:<< Ignition on and No MAP Sensor DTCs set.
>>Set Condition:<< The Powertrain Control Module (PCM) detects that the sensor input voltage does not fall within a valid range based on engine speed and load. Two Trip Fault. (Electronic Throttle Control) ETC light will illuminate. P2135 should set with this code also.

Possible Causes
EXCESSIVE RESISTANCE IN THE (K22) TP SENSOR NO. 1 SIGNAL CIRCUIT
EXCESSIVE RESISTANCE IN THE (K122) TP SENSOR NO. 2 SIGNAL CIRCUIT
EXCESSIVE RESISTANCE IN THE (F855) 5-VOLT SUPPLY CIRCUIT
EXCESSIVE RESISTANCE IN THE (K922) TP SENSOR RETURN CIRCUIT
(K22) TP SENSOR NO. 1 SIGNAL CIRCUIT SHORTED TO THE (K122) TP SENSOR NO. 2 SIGNAL CIRCUIT
THROTTLE POSITION SENSOR/THROTTLE BODY
POWERTRAIN CONTROL MODULE (PCM)

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Refer to Pre-Diagnostic Troubleshooting Procedure .