What it means
Throttle/fuel inhibit B line stuck low. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Throttle/fuel inhibit B is a control line used by the vehicle to allow or prevent engine fueling or throttle operation. The control module monitors the line's electrical state and sets P218D when it detects a low state, which can happen if the wire is shorted to ground or its connection is compromised.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light on
- Engine may crank without starting or fail to start
- Reduced throttle response or engine power
- Security or transmission warning light may come on
How to diagnose it
- Check freeze-frame data and scan for related security, throttle, or transmission codes to see when the inhibit line fault occurs and what other systems are involved.
- With the fault present, inspect the throttle/fuel inhibit B wire and connectors for chafing, moisture, corrosion, loose pins, or pins pushed back from the connector face.
- While watching the relevant scan data or circuit state, gently move the B-line harness to see whether the fault changes with harness movement.
- Use the wiring diagram to identify the B line, then check for an unintended connection to ground and inspect connector contact quality.
- If the wiring and connections are sound, test the connected control modules or components according to the manufacturer's diagnostic procedure.
Common fixes
- Repair chafed insulation on the throttle/fuel inhibit B wire.
- Clean or repair corroded or loose B-line connector terminals.
- Repair a short to ground in the inhibit B circuit.
- Replace a failed connected component or module only after circuit tests confirm the fault.
Can I keep driving?
If the engine starts and runs normally, limit driving and avoid relying on normal throttle response; the fault can cause reduced power or a no-start. If it cranks without starting or power drops sharply, stop somewhere safe and arrange diagnosis.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.