DTC 21

Fig. 004 - Wiring Diagram for Code 21 TPS Circuit High. VIN C:

CODE 21, TPS CIRCUIT HIGH

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle blade. Signal voltage will vary from about .5 volts at idle to 4.5 volts at wide open throttle.
The TPS signal is one of the most important inputs used by the ECM for fuel control and for most of the ECM control outputs.
Trouble Code 21 means that the ECM has seen a high TPS voltage for:
a. Over about 10 seconds in WOT
b. Below 1000 RPM
c. Below a specified engine load.
Due to the pull-up resistor between Terminals "15" and "5" within its ECM, an open in the TPS circuit will place about 5 volts (high TPS signal) at Terminal "5" of the ECM.

Fig. 003 - Chart - Code 21 Throttle Position Sensor Circuit (Open or Misadjusted).:

1. Checks the circuit from the TPS connector back to the ECM. Both wires should read about 5 volts.
2. Checks to see if the fault of low voltage at the TPS connector is an open in the circuit or a faulty ECM connector or ECM. A normal reading at the ECM is about 5 volts.
3. This step simulates closed throttle so, dwell should increase if the ECM is good.
4. This step tests the resistance of the TPS switch itself. A normal reading is under 20,000 ohms.