Copyright © 1998 General Motors Corp. 6–29
WTEC II ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL
Main code 21 indicates the throttle position sensor has been retracted or extended by its linkage into an error zone.
This may be due to a fault with the sensor, or a fault in the wiring to the sensor or to the ECU. This code may also
indicate a PWM signal problem. Code 21 12 is set when the ECU receives TPS counts of 14 or less. Code 21 23 is
set when the ECU senses TPS counts of 233–255. Whenever a Code 21 XX condition is detected, the system
defaults to 100 percent throttle and part throttle shifts will be abrupt.
NOTE: Whenever Code 21 12 or 21 23 is set and the ECU was programmed after 9/26/94, the SERVICE icon
on the shift selector will be illuminated.
NOTE: Code 21 XX in conjunction with Code 33 XX or Code 14 XX indicates the potential loss of common
ground wire 135 between the throttle, temperature sensor, and oil level sensor.
Active Indicator Clearing Procedure:
• Power down
• Manual
• Self-clearing
NOTE: Before troubleshooting, read Pages 6–17 and 6–18 of Section 6–5. Also, check the ECU input voltage.
Troubleshooting:
1. Plug in the DDR, select Diagnostic Data, and read throttle counts and percent. If the TPS failed
high (Code 21 23), the problem may be toward the full throttle end of the TPS travel. If the TPS
failed low (Code 21 12), the problem may be at the closed throttle end of the TPS travel.
2. If counts are high but the percentage never reaches 100 percent, TPS linkage may have bound up
and overstroked the TPS to set a false 100 percent reading. After TPS overstroking ceases, the TPS
will not automatically return to 100 percent. After the TPS is correctly installed and adjusted, use
the Pro-Link
®
to reset throttle calibration or cycle the ignition 5 times to reset the 0 percent and
100 percent settings. See TPS section of this book (Appendix F) for installation and adjustment
procedures.
3. If the throttle counts do not change or are erratic, check the throttle sensor wiring for opens, shorts
between wires, or shorts-to-ground. Also check for correct TPS voltages using test wiring harness
J 41339. If wiring problems are found, isolate and repair the fault (refer to Appendix E for repair
information).
4. If the wiring is satisfactory, replace the throttle position sensor and adjust its linkage so the counts
are not in the error zones (See Appendix F).
5. If the throttle sensor and its linkage adjustment are correct and the wiring to the sensor is
satisfactory, the condition is intermittent. Replace the sensor and properly adjust the new sensor.
6. If the condition recurs, use spare harness wires for the throttle sensor circuit. See Appendix D for
available spare wires and Appendix E for connector repair information.
Main Code Subcode Meaning
21 12
Throttle position sensor failed low and
ECU signals 100 percent throttle
21 23 Throttle position sensor failed high
CODE 21 XX — THROTTLE POSITION SENSOR OR PWM FAULT OR
ADJUSTMENT (Figures 6–5, 6–6)
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