P218B: Throttle/Fuel Inhibit B Circuit

What does P218B mean?

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.

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

Symptoms

• Check engine lamp on the following drive
• Possible power limitation

Common causes

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

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