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DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P20DA

P20DAExhaust Aftertreatment Fuel Supply Control Circuit High

P20DA means the engine computer has detected an abnormally high voltage on the control circuit for the exhaust aftertreatment fuel supply, which is the system that injects diesel fuel into the exhaust to regenerate the diesel particulate filter. The computer expects a certain voltage range on the control wire, and a reading above that range indicates a short to voltage or an open control circuit.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms.
  • Reduced engine power or limp mode if the fault triggers protective strategies.
  • A noticeable decrease in fuel economy due to failed regeneration attempts.
  • Frequent or forced active regenerations that may not complete successfully.
  • Possible white smoke or diesel smell from the exhaust if excess fuel is injected.
  • In some cases, the vehicle may enter a regeneration inhibit mode, leading to a clogged particulate filter over time.

Common causes, most likely first

  1. A short to voltage in the fuel supply control circuit wiring, often caused by chafed insulation or contact with a hot or moving component.
  2. A faulty exhaust aftertreatment fuel injector (also called the seventh injector) with an internal short.
  3. A failed fuel supply control module or driver circuit inside the engine control module (ECM).
  4. Corroded, loose, or damaged electrical connectors at the fuel injector or ECM.
  5. An open circuit in the control wire, which can cause the ECM to see a high voltage on the return side.
  6. A poor ground connection for the fuel supply control circuit, leading to abnormal voltage readings.

How to diagnose and fix it

  1. Perform a visual inspection of the fuel supply control circuit wiring and connectors for damage, corrosion, or loose pins.
  2. Use a digital multimeter to check for battery voltage on the control wire with the key on and engine off; compare to manufacturer specifications.
  3. Disconnect the fuel injector and measure resistance across its terminals to check for an internal short or open coil.
  4. Check for continuity and resistance in the control wire between the ECM and the fuel injector to rule out an open or shorted wire.
  5. Inspect and test the ground circuit for the fuel supply control system to ensure a clean, tight connection.
  6. If the wiring and injector test good, substitute a known-good fuel injector or control module to see if the code changes.
  7. Clear the code and perform a road test with a scan tool to verify the repair and ensure the monitor runs without resetting the fault.

What the voltage reading really tells you

  • A high voltage on the control circuit often indicates a short to voltage rather than a failed injector, so always check for rubbed wires near hot exhaust components first.
  • The code can be set by a faulty ground connection that causes the ECM to see a higher-than-expected voltage on the control wire, which is a commonly overlooked cause.
  • Some technicians replace the expensive fuel injector only to find the real problem is a chafed wire in the harness, so thorough circuit testing saves money.
  • This code does not always mean the fuel injector itself has failed; the fault could be in the control module or the wiring, so do not jump to parts replacement.
  • A weak battery or charging system issue can cause erratic voltage readings that mimic a circuit fault, so verify battery and charging system health before diagnosing.

Can I keep driving with P20DA?

You can usually drive the vehicle with this code, but avoid heavy loads and long trips because the particulate filter may not regenerate properly, which can lead to a clogged filter and reduced performance. If the engine enters limp mode or you notice excessive smoke, have the vehicle 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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