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DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P20D3

P20D3Exhaust Aftertreatment Fuel Injector B Control Circuit Low

P20D3 means the powertrain control module (PCM) has detected a low-voltage condition on the control circuit for the exhaust aftertreatment fuel injector on bank B. This injector sprays diesel fuel into the exhaust stream to raise temperature for the diesel particulate filter (DPF) regeneration, and the PCM monitors the circuit for expected voltage; a low reading indicates a short to ground, an open circuit, or excessive current draw.

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
  • Frequent or failed DPF regeneration, leading to a plugged filter over time
  • Possible rough running or misfire if the injector is shorted internally
  • Exhaust smoke or odor changes if the injector is stuck open or closed
  • A stored pending code or freeze-frame data showing low circuit voltage

Common causes, most likely first

  1. Damaged or chafed wiring harness between the PCM and the exhaust aftertreatment fuel injector
  2. Corroded, loose, or water-intruded connector pins at the injector or PCM
  3. Failed exhaust aftertreatment fuel injector with an internal short to ground
  4. Open circuit in the control wire or a blown fuse supplying the injector
  5. PCM driver circuit fault, though this is less common than wiring or injector issues
  6. Exhaust system modifications or damage that pinched the injector wiring
  7. Aftermarket accessories or poor previous repairs tapping into the circuit

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data to confirm P20D3 is active and not a history code
  2. Visually inspect the injector, connector, and harness routing for chafing, corrosion, or heat damage
  3. Disconnect the injector and measure resistance across its terminals, comparing to manufacturer specifications
  4. Check for battery voltage on the supply side of the injector connector with the key on and engine off
  5. Perform a voltage drop test on the ground side of the control circuit while cranking or commanding the injector on
  6. Inspect and test the PCM connector pins and, if needed, back-probe the control wire for continuity to the PCM
  7. Repair or replace the faulty wiring, connector, or injector, then clear codes and verify the repair with a road test that triggers regeneration

What a low injector circuit really means

  • A low-voltage code often results from a short to ground in the harness rather than a failed injector, so always inspect wiring before condemning the part.
  • The exhaust aftertreatment fuel injector is not the same as the engine fuel injectors, and mixing up the two circuits leads to unnecessary engine fuel system repairs.
  • A weak or failing battery can cause false low-voltage codes on this circuit, so verify charging system health before deeper diagnostics.
  • Some vehicles will not set this code until a regeneration is commanded, so a simple key-on scan may show it as pending rather than confirmed.
  • Aftermarket exhaust work or off-road modifications frequently pinch or melt the injector harness, creating a low circuit that looks like an injector failure.

Can I keep driving with P20D3?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads and long trips because a failed regeneration can clog the diesel particulate filter and lead to expensive repairs. If the engine enters limp mode or you notice excessive exhaust smoke, stop driving and seek professional diagnosis.

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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