P0121

THROTTLE POSITION SENSOR





Symptom Of Fault.
The CHECK ENGINE lamp (MIL) is on.
High idling speed. A/C compressor does not work.

Conditions.
P0120: All-embracing DTC.
P0121: Engine running and throttle closed: >1.0 V or <0.24 V
P0122: Engine running: <0.2 V for 5 seconds.
P0123: Engine running: >4.96 V for 5 seconds.

Diagnostic Help.
The throttle position sensor reading can be obtained on an ISAT scan tool.

- Turn the ignition switch to the ON position and then back to the OFF position.
- Connect an ISAT scan tool.
- Select "READ FUNCTIONS".
- Select "THROTTLE POSITION".

If the throttle position sensor is in perfect working order the ISAT scan tool should show the current throttle position, 10-90% (0.5 to 4.5 V) from fully up (not depressed) to fully depressed accelerator.

Checking The Wiring.
Intermittent faults may occur as a result of occasional short circuits and breaks in the wiring. Jiggle the leads and in-line connectors at several places and in different directions to reveal faults in the wiring harness. Observe the multimeter, ISAT scan tool or test lamp while carrying out this check.





Diagnostic Procedure.
1. Check the throttle position sensor's ground connection and power supply

- Turn the ignition switch to the ON position and then back to the OFF position.
- Unplug the throttle position sensor's 3- pin connector.
- Take voltage readings on the connector.

^ pin 1 to 13: about 5 V
^ B+ to pin 2: about 12 V.

Are all voltage readings correct?
YES: Continue with point 2.
NO: Rectify the lead in question and proceed to point 3.





2. Check the engine control module's throttle position input

- Turn the ignition switch to the ON position and then back to the OFF position.
- Unplug the throttle position sensor's 3-pin connector.
- Connect an ISAT scan tool.
- Select "READ FUNCTIONS".
- Select "THROTTLE POSITION". The reading obtained on the ISAT scan tool should be about 99%.
- Connect a jumper lead between pins 3 and 2 of the throttle position sensor's connector. The reading obtained on the ISAT scan tool should be about 0%.

Are all readings OK?
YES: Change the throttle position sensor and continue with point 3.
NO: Rectify the lead in question and proceed to point 3.





3. Final check:

- Clear the diagnostic trouble code.
- Implementation of driving cycle:
Drive the car at varying loads and engine rpm for 5 minutes.
- Evaluation of driving cycle:
Check whether the diagnostic trouble code has recurred.

Has the diagnostic trouble code recurred?

YES: Continue at "Before Replacing a Control Module. Component Tests and General Diagnostics
NO: The remedial measure taken was correct.