P218B: Throttle/Fuel Inhibit B Circuit

P218B is a general electrical fault in the second throttle/fuel inhibit line, B. An inhibit line carries a signal with which another unit can tell the engine computer to keep the throttle closed or stop fuelling. No manufacturer documents the B line publicly. The only published use of this function concerns the A line: GM's 2005 table for the 3.5-litre V6 (L66) places it in the throttle valve control section, where the injection and throttle processors check each other, and monitors it with P2553-P2555 once per drive cycle after ignition off, lighting the MIL on the next drive cycle. California's OBD rule requires inputs of this kind to be checked for circuit faults. Open wires, corroded pins and module connector faults come first; reduced power is possible.

Low severity. Can I keep driving?You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.

Symptoms

Check engine lamp on the following drive
Possible power limitation

Most likely causes

Open or high-resistance inhibit B wire
Corroded or loose pins at the engine or throttle module connector
Fault in the unit that drives the inhibit signal

What to check, in order

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

Check the connector and wiring
Use live data to compare the reading with actual conditions
Measure power, ground, and signal
Replace the sensor if the circuit is good

Good to know

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

What each character of P218B means

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

Frequently asked questions

Can I keep driving with code P218B?

You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.

What causes code P218B?

The most common causes are: open or high-resistance inhibit B wire; corroded or loose pins at the engine or throttle module connector; fault in the unit that drives the inhibit signal.

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.