WTEC II ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL
F–2 Copyright © 1998 General Motors Corp.
APPENDIX F — THROTTLE POSITION SENSOR ADJUSTMENT
A. Description of Operation
(cont’d)
3. Throttle percentage is proportional to counts; low counts correspond to low percent and high
counts correspond to high percent (Table F–1, Page F–4).
4. The conversion from counts to percent throttle is performed easily once the idle and full throttle
positions are set (see adjustment procedures below). The idle and full throttle positions correspond
to counts which can be viewed with a diagnostic tool. The ECU determines percent throttle by the
equation:
Where:
Idle Count = Count on diagnostic tool when engine is idling.
Current Count = Count on diagnostic tool at the present throttle position.
Full Throttle Count = Count on diagnostic tool at wide open throttle.
NOTE: Refer to Appendix N for DDR information.
5. The throttle position sensor is self-calibrating within its normal operating range. Each time the
vehicle is started and the ECU is initialized, the idle counts that are used for closed throttle are
increased by 15 counts from its previous lowest reading. Also, the wide open throttle counts are
reduced by 15 counts from its previous highest reading. Once new counts are read from the
current sensor position, the idle and wide open throttle count set points are continually readjusted
to the lowest and highest counts, respectively. This compensates for fuel control system wear or
previous mechanical adjustment. One area of particular concern is when the throttle sensor
extends into the error zone. This indicates a TPS misadjustment to the ECU and 100 percent
throttle is assumed until readjustment is performed. Simply clearing the Code 21 XX will not
resolve the 100 percent (WOT) shifting situation.
NOTE: After replacing or adjusting the throttle position sensor linkage, the technician should use the
diagnostic tool to clear the throttle calibration. Go to the DDR selection menu and locate ACTION
REQUESTS. Select RESET THROTTLE CALIBRATION and ENTER to set the 0 percent throttle
counts. After the idle counts are established, the throttle should be moved to the Full position to
establish the full or Wide Open Throttle (WOT) position (100 percent). The full throttle counts will be
the same as the idle counts until the throttle is moved. The full throttle counts are set when maximum
travel is reached so stopping before actual full throttle will set the 100 percent point artificially low.
Refer to Figure F–2 for proper counts and percentage. Refer to Figure F–3 for illustration of throttle
position adjustment.
Current Count — Idle Count
Full Throttle Count — Idle Count
% Throttle = x 100
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