Code 21
Code 21 is a diagnostic trouble code related to the Throttle position sensor circuit on the Pontiac Fiero.
Code 21 indicates that the ECM is seeing a throttle position sensor signal voltage that is higher than expected.
Overview
The throttle position sensor, often abbreviated as TPS, tells the ECM how far the throttle is opened.
The ECM uses the TPS signal for fuel control, acceleration enrichment, idle control, deceleration behavior, and general drivability calculations.
Code 21 is set when the ECM detects a TPS signal voltage that is too high for the current operating condition.
Flash pattern
Code 21 is displayed as:
- Two flashes
- Pause
- One flash
This represents code 21.
Animated flash pattern:
Meaning
Code 21 usually indicates a high-voltage condition in the throttle position sensor circuit.
Possible causes include:
- Misadjusted throttle position sensor
- Faulty throttle position sensor
- TPS connector problem
- TPS wiring problem
- Short to voltage in the TPS signal circuit
- Throttle linkage or throttle plate not returning correctly
- ECM input problem
Symptoms
Possible symptoms may include:
- Check engine light
- High idle
- Poor throttle response
- Hesitation
- Surging
- Poor fuel economy
- Harsh or unusual drivability behavior
- Transmission-related symptoms on automatic cars in some conditions
Diagnosis
Basic diagnostic checks include:
- Confirm that Code 21 is present.
- Inspect the throttle position sensor connector.
- Inspect TPS wiring for damage.
- Check that the throttle linkage moves freely.
- Check that the throttle plate returns fully.
- Check TPS adjustment if applicable.
- Check TPS voltage with the throttle closed and while opening the throttle.
- Check for other stored trouble codes.
- Check ECM connector condition if the sensor and wiring appear correct.
Related codes
Related TPS and drivability codes include:
Notes
Code 21 should not automatically be treated as a failed sensor. A misadjusted TPS, sticking throttle, wiring fault, or connector issue can also cause the ECM to see an incorrect throttle signal.
The TPS signal should change smoothly as the throttle is opened. Sudden jumps, dropouts, or incorrect closed-throttle voltage can cause drivability problems.