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DTC codes / P21xx · Fuel and air metering / P218F

P218FReductant No Flow Detected

P218F means the engine control module has commanded the selective catalytic reduction system to inject diesel exhaust fluid, but it has detected no corresponding flow or pressure change in the reductant line. The computer is not seeing the expected feedback from the dosing module or pressure sensor, so it flags a no-flow condition.

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

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms at first
  • A message on the dash warning that the vehicle will be speed-limited or will not restart after a certain number of engine starts
  • Reduced engine power or a limp-home mode once the fault is active for a short period
  • Rough running or increased exhaust smoke if the system has been disabled and the engine is operating in a fallback strategy
  • A noticeable increase in diesel exhaust fluid consumption in some cases, or no consumption at all if the pump has failed
  • An audible whine or lack of the usual pump priming sound when the key is turned on

Common causes, most likely first

  1. A failed or clogged reductant dosing injector or nozzle that prevents fluid from being sprayed into the exhaust
  2. A reductant pump that has seized, lost its prime, or has an internal electrical failure
  3. A blocked, kinked, or frozen reductant line between the tank and the dosing module
  4. A faulty reductant pressure sensor or level sensor providing implausible readings to the control module
  5. Air trapped in the reductant system after a refill or repair, causing a temporary no-flow condition
  6. A blown fuse or corroded connector in the reductant pump circuit
  7. Crystallized diesel exhaust fluid in the line or injector due to prolonged sitting or a previous leak

How to diagnose and fix it

  1. Check the diesel exhaust fluid level and quality, and top up with the correct specification fluid if low or contaminated
  2. Inspect the reductant lines and connections for kinks, leaks, or crystal buildup, and clear any blockage
  3. Command the reductant pump on with a scan tool and listen for operation while watching live pressure data to confirm whether the pump is running and building pressure
  4. Test the reductant pressure sensor signal for plausibility against a known-good value or a manual gauge
  5. Remove and inspect the dosing injector for clogging or crystallization, and clean or replace it if flow is restricted
  6. Check the pump circuit for power, ground, and control signal integrity, including fuses and relays
  7. Perform a reductant system bleed or prime procedure with the scan tool after any repair to remove trapped air

What a no-flow code really tells you

  • A no-flow code does not automatically mean the pump is dead; a stuck-closed dosing injector or a pinched line will produce the same pressure signature and is often the cheaper fix.
  • Crystallized diesel exhaust fluid from a small leak or from the vehicle sitting for weeks can block the injector without any stored pump fault, so always inspect the nozzle before condemning the pump.
  • Some vehicles will not run the reductant pump unless the engine is running and exhaust temperature is above a threshold, so a key-on pump command may show no flow even on a healthy system.
  • Air introduced during a routine diesel exhaust fluid refill can set a temporary no-flow code that clears after a proper bleed cycle, so do not replace parts before running the prime procedure.
  • A failing reductant level sensor can report full when the tank is nearly empty, causing the pump to run dry and set a no-flow code that looks like a pump failure.

Can I keep driving with P218F?

You can usually drive a short distance to a repair shop, but avoid long trips or heavy loads because the vehicle may enter a speed-limited limp mode or refuse to restart after a set number of shutdowns. Do not ignore the warning if the dash displays a countdown to no-restart.

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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