Part 2 of 2

Code Chart 21:

TPS Circuit:

CIRCUIT DESCRIPTION:
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle valve. Signal voltage will vary from .33 to 1.33 volts 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 Engine Control Module (ECM) for fuel control and for many of the ECM controlled outputs.

TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step checks to see if DTC 21 is the result of a hard failure or an intermittent condition.

2. This step simulates conditions for a DTC 21. If the scan tool displays over 4 volts, the ECM and wiring are OK.

3. This simulates a high signal voltage to check for an open or short in CKT 417. The scan tool will not read battery voltage, but the ECM should recognize the signal on CKT 417.

4. Refer to Service and Repair for TP sensor replacement procedures.

5. The 5 volt reference for the MAP sensor and the A/C refrigerant pressure sensor connect to the same 5 volt power supply in the ECM. If the 5 volt reference circuit to the MAP sensor and A/C refrigerant pressure sensor has a short to ground, the Throttle Position (TP) sensor 5 volt reference circuit will also have a short to ground because they connect to the same power supply in the ECM. A short to ground on either 5 volt reference circuit does not damage the ECM 5 volt power supply. When the short is repaired, the ECM 5 volt supply will return to normal.

DIAGNOSTIC AIDS:
A scan tool displays throttle position in volts. Closed throttle voltage should be .33 to 1.33 volts. TP sensor voltage should increase at a steady rate as throttle is moved to WOT.

If DTC 21 is intermittent, Testing and Inspection