P218A: Throttle Actuator B Control System - Idle Position Not Learned

P218A is the throttle B counterpart of P2176: on engines with a second electronic throttle, usually one per cylinder bank, that second unit failed to learn its closed rest position. GM's 2023 table 23OBDG07 runs the same three-step learn for bank 2 as for bank 1. First the plate must reach the closed target within 1.5 %, then the motor has to press it onto the stop with enough duty cycle, and finally the stored voltages must fall inside 0.33-0.58 V for sensor 1 and 4.42-4.67 V for sensor 2; any failed step stores the code within one trip. No other manufacturer documents P218A publicly. Ice, carbon, a weak motor or wiring faults at throttle B are typical causes, and engine power may be limited. Electrical motor faults of throttle B use P210A.

High severity. Can I keep driving?Be careful: the car may suddenly lose power. If it goes into limp mode, get off the highway and calmly make your way to a repair shop.

Symptoms

Check engine lamp
Uneven idle between the banks
Reduced power

Most likely causes

Carbon or ice keeping throttle B off its closed stop
Weak motor or gear wear in throttle unit B
Position sensors of throttle B outside the learn window
Supply or signal wiring fault at throttle B

What to check, in order

Start with the simplest. You can tick off each step.

Check the pedal and throttle connectors
Use live data to confirm that both sensors rise smoothly and consistently
Clean the throttle if it has carbon buildup
Run the relearn procedure with the scanner if the manufacturer requires it
Replace the part identified by the diagnosis

Good to know

Repair difficulty: medium
It can trigger limp mode.
It affects emissions.

What each character of P218A means

P: Powertrain: engine and transmission
2: Generic code: same on every make
1: Air and fuel
8A: Specific fault in that system

Frequently asked questions

Can I keep driving with code P218A?

Be careful: the car may suddenly lose power. If it goes into limp mode, get off the highway and calmly make your way to a repair shop.

What causes code P218A?

The most common causes are: carbon or ice keeping throttle B off its closed stop; weak motor or gear wear in throttle unit B; position sensors of throttle B outside the learn window.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.