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

What does P218A mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine lamp
• Uneven idle between the banks
• Reduced power

Common causes

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

Likelihood is a general estimate across vehicles; your make and model may differ.