P1221

Throttle Position (TP) Sensor 1-2 Correlation

Car Fault Codes Chevrolet Fuel & air

Can you still drive? With care, short trips only

Who can fix it? Needs a workshop

Typical repair time 30 minutes – 2 hours

Typical cost SAR 100 to 2,500

What it means

This is a Chevrolet (GM) manufacturer-specific code, and the same number can mean something different on other makes. Each of the two throttle position sensors gives an acceptable voltage on its own, but the two readings do not agree on the same throttle opening. The usual cause is extra resistance in a connector or a worn track inside the throttle body sensor.

Models covered: Chevrolet (GM) models with electronic throttle control, mainly around 1997–2006.

Symptoms4

Sudden reduced engine power while driving.
Check engine light on with a reduced power message.
Hesitant acceleration that does not match pedal input.
Normal operation may return after a restart, then the fault repeats.

Possible causes5

Corroded or damp throttle body connector terminals causing extra resistance.
A worn internal track on one sensor inside the throttle body.
A weak ground or reference shared by both sensors.
A damaged wire that shifts one sensor's voltage without fully breaking it.
A fault in the throttle actuator control (TAC) module or engine computer (rare).

How to diagnose5

Review freeze frame data to see the throttle opening when the code set.
Graph both sensor voltages on a scan tool while slowly opening the pedal and look for a point where they drift apart.
Inspect and clean the connector, then compare again.
Measure voltage drop on the ground and reference circuits and compare with specification.
If the wiring is good and the mismatch remains, the throttle body is the likely cause.

How to fix5

Clean the throttle body connector and treat corrosion.
Repair the ground or wire causing the voltage drop.
Replace the throttle body if one built-in sensor is confirmed worn.
Perform the throttle relearn after any replacement.
Clear the codes and drive with varied pedal positions to confirm the code does not return.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

Cleaning the connector or fixing a ground keeps the cost low, while replacing the electronic throttle body puts it at the top of the range.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Each sensor looks fine alone, so why the code?

The computer also checks that both readings describe the same opening. A difference larger than allowed means one of them cannot be trusted.

Will cleaning carbon from the throttle fix it?

Usually not. This code is about the two sensor signals, not how the plate moves. Cleaning helps performance codes, but here the connector and sensor matter most.

What is the generic equivalent?

Newer models use the generic code P2135 for throttle sensor correlation.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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