W T E C I I I E L E C T R O N I C C O N T R O L S T R O U B L E S H O O T I N G M A N U A L
The throttle sensor must have been recognized by autodetect or manually selected using the Pro-Link® (see
WTEC III Pro-Link® Manual) before these codes can be logged. See Paragraph 19 for further information.
Main code 21 indicates the throttle position sensor has been retracted or extended by its linkage into an error zone.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. A PWM signal is proportional to throttle position and comes from some source
other than an analog throttle position sensor. 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 233255. Whenever a code 21 XX condition is detected, the
system uses default throttle values and shifts will not adapt.
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:
Before troubleshooting, read Paragraph 56. Also, check the ECU input voltage.
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.
Code 21 12 may occur when the throttle source is J1587 or J1939 and an analog throttle source is
falsely detected. This condition may be due to a problem in an unused TPS branch of a universal
external harness. To prevent this occurrence, remove wire 156 from the ECU connector and insert a
cavity plug in the space vacated by the wire. Be sure that the unused TPS branch is routed away from
potential induced voltage sources and the connector is protected from external contamination.
Code 21 12 can result when the +5V line (wire 124) which powers the analog sensor is shorted to
ground. Wire 124 also powers the OLS, RMR, retarder temperature sensor, sump temperature sensor,
and shift selector and is present in all three ECU connectors.
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.
Throttle position sensor failed low and
ECU signals throttle default value
Throttle position sensor failed high and
ECU signals a throttle default value
CODE 21 XX THROTTLE OR PWM FAULT (Figure 54)