Powertrain, generic (extended)

P218C Throttle/Fuel Inhibit B Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P218C means the inhibit B line is electrically within limits, yet its state or response does not fit what the controller expects: it may signal a lock when none is requested, or fail to react during a function test. No manufacturer documents P218C publicly. GM's 2005 table for the 3.5-litre V6 (L66) shows the analogous test on line A as P2553: a function check of the relay path, judged by a normal signal on the serial data link with battery voltage above 7 V, run once per drive cycle after ignition off and lighting the MIL on the next drive. California's OBD rule asks for plausibility checks of such inputs. Likely causes are a sticking relay, a slow-switching driver or software mismatch between the modules. P218D/P218E cover hard low and high faults.

Likely causes

Relay in the inhibit path sticking or switching late
Software versions of the communicating modules do not match
Intermittent contact causing implausible line states

Symptoms

  • Check engine lamp on the next drive
  • Occasional power reduction without obvious reason

Repair estimate

DifficultyHardWorkshop job
Parts and labour€50–700
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

throttle fuel inhibit

Related codes

P218BP218DP218EP2553

References: gsi.ext.gm.com, law.cornell.edu.