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DTC codes / P21xx · Fuel and air metering / P218E

P218EThrottle/Fuel Inhibit B Circuit High

P218E indicates that the powertrain control module has detected a high-voltage condition on the throttle/fuel inhibit B circuit, which is a safety path used to cut throttle or fuel delivery under certain fault conditions. The computer compares the commanded state of this circuit to the actual feedback signal and sets the code when the circuit voltage stays above the expected threshold for a calibrated time.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light or service engine soon light, often with no other noticeable symptoms
  • Reduced engine power or limp-home mode, where the throttle response becomes severely limited
  • The engine may crank but fail to start, or stall immediately after starting, if fuel delivery is inhibited
  • Intermittent hesitation or sudden loss of power during acceleration when the circuit acts up
  • A stored code P218E with no drivability complaint, especially after a battery or throttle body service

Common causes, most likely first

  1. A short to voltage on the throttle/fuel inhibit B circuit wiring, often from chafed insulation or pinched harness
  2. A faulty throttle actuator control module or electronic throttle body internal fault affecting the inhibit circuit
  3. Corroded or loose terminals at the throttle body, pedal, or powertrain control module connectors
  4. A failed or sticking throttle/fuel inhibit relay that keeps the circuit energized when it should be off
  5. Water intrusion into a connector or module causing unintended voltage on the inhibit circuit
  6. A software calibration issue in the powertrain control module that misinterprets the inhibit circuit voltage

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes, freeze-frame data, and the inhibit circuit voltage parameter to confirm the fault is current
  2. Visually inspect the throttle body, pedal, and powertrain control module connectors for corrosion, water, or loose pins, and repair as needed
  3. Back-probe the throttle/fuel inhibit B circuit at the module and measure voltage with the key on to verify the high-voltage condition
  4. Disconnect the inhibit relay or actuator and recheck the circuit voltage to isolate whether the fault is in the wiring or a component
  5. Perform a wiggle test on the harness while monitoring the inhibit circuit voltage to locate intermittent shorts
  6. Repair or replace the shorted wiring section, relay, or throttle body as indicated by the isolation tests
  7. Clear the codes, perform a throttle body relearn or idle relearn if required, and verify the repair with a road test

What the inhibit circuit really does

  • The throttle/fuel inhibit circuit is a safety feature designed to cut power if the computer detects a runaway throttle condition, so a fault here can cause a no-start or limp mode even when the engine itself is healthy.
  • Many technicians replace the throttle body first, but a chafed wire near the pedal assembly or a corroded ground can set P218E without any fault in the throttle body itself.
  • A weak or failing battery can cause momentary voltage spikes that trigger P218E, so always check battery health and charging system output before condemning expensive modules.
  • After any throttle body or pedal replacement, a relearn procedure is mandatory on many vehicles; skipping it can leave the inhibit circuit voltage out of range and set the code again.
  • The code can be stored by a low-voltage event during engine cranking, so check for a history of other low-voltage codes before chasing the inhibit circuit.

Can I keep driving with P218E?

If the vehicle is in limp mode or will not start, do not drive it because the inhibit circuit can cut throttle or fuel without warning. If the only symptom is a warning light and the car drives normally, you can drive cautiously to a repair shop, but avoid heavy acceleration and have it checked promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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