A malfunction in the throttle position sensor circuit will set diagnostic trouble Codes 21 and/or 22. For testing and adjusting procedures, see THROTTLE POSITION (TP) SENSOR in ADJUSTMENTS article in this section. Use the following procedure to diagnose TP sensor.
Using ohmmeter, measure resistance or continuity of throttle position sensor between designated terminals with selected feeler gauge thickness between throttle lever and stop screw. See Fig 1 . Adjust or replace TP sensor if resistance is not within specification. See THROTTLE POSITION (TP) SENSOR RESISTANCE table.

Fig 1: Identifying TP Sensor Terminals

Courtesy of GENERAL MOTORS CORP.

THROTTLE POSITION (TP) SENSOR RESISTANCE

Application

Ohms

Standard Emissions

Between Terminals 1 & 2 ⁽¹⁾

0-5000

Between Terminals 1 & 2 ⁽²⁾

Infinity

Between Terminals 1 & 2 ⁽³⁾

0-5000

Between Terminals 1 & 3 ⁽³⁾

240-1140

Between Terminals 1 & 3 ⁽⁴⁾

3170-6600

Between Terminals 1 & 4

4370-8130

Upgraded Emissions

⁽⁵⁾

⁽¹⁾	With .012" (.30 mm) feeler gauge installed between throttle stop screw and lever.

⁽²⁾	With .035" (.89 mm) feeler gauge installed between throttle stop screw and lever.

⁽³⁾	Throttle valve at idle position.

⁽⁴⁾	Throttle valve at fully open position.

⁽⁵⁾	For information on TP sensor, see THROTTLE POSITION (TP) SENSOR in ADJUSTMENTS article in this section.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Throttle Position (TP) Sensor