Powertrain Controls - ECM/PCM

DTC 21 Throttle Position Sensor Circuit (Signal High):

Throttle Position (TP) Sensor Schematic:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle blade. Signal voltage will vary from about 0.5 at idle to about 4.5 volts at Wide Open Throttle (WOT).
The TP sensor signal is one of the most important inputs used by the Powertrain Control Module (PCM) for fuel control and for most of the PCM control outputs.

DIAGNOSTIC TROUBLE CODE (DTC) 21 WILL SET WHEN
TP sensor signal voltage is greater than 3.1 volts, MAP is less than 52 kPa with both conditions met for 2 seconds.

ACTION TAKEN (PCM will default to)
The PCM will determine fuel and air calculations using calibrated values from a default table (0.93V). The MIL will become illuminated.

DTC 21 WILL CLEAR WHEN
A current DTC 21 will clear when high signal voltage above the calibrated threshold is no longer detected. A history DTC 21 will clear after 50 consecutive ignition key cycles without a current DTC 21 being stored.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart,
1. With throttle closed, the TP sensor should read less than 1.25 volts. If it doesn't, make sure cruise control and throttle cables are not being held open.
2. With the TP sensor disconnected, the TP sensor voltage should go low if the PCM and wiring are OK.
3. Probing CKT 452 with a test light to 12 volts checks the sensor ground circuit. A faulty sensor ground will cause a DTC 21.

DIAGNOSTIC AIDS
A Tech 1 scan tool reads throttle position in volts. Should read less than 1.25 volts with throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT. Tech 1 will also display throttle angle. Key "ON" engine "OFF" Tech 1 will display less than 100% at WOT.
An open in CKT 452 will result in a DTC 21.

Refer to Intermittents under Computers and Control Systems/System Diagnosis/Diagnosis By Symptom. - Intermittent Malfunctions