P20D3

Code

Generic P — Powertrain

Exhaust Aftertreatment Fuel Injector B Control Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 29 EN: 37 RU: 24

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Page language: EN

Causes

Short to ground in the injector B control wiring
Open or shorted injector B solenoid/coils
Poor or corroded connector or terminal at the injector
Faulty injector driver in the PCM/ECM
Blown fuse or faulty relay supplying the injector circuit
Aftertreatment module or dosing pump wiring fault

Symptoms

Malfunction Indicator Lamp (MIL) or Check Engine Light illuminated
Stored P20D3 trouble code (may appear with related aftertreatment codes)
Reduced or failed aftertreatment dosing (SCR/DPF regeneration issues)
Possible increased NOx or failed emissions test
Reduced engine or aftertreatment system performance, possible limp mode

What to check

Retrieve freeze frame and related codes; note conditions when code set
Visual inspection of injector B connector, wiring harness, and ground routing for damage, melting or corrosion
Check battery voltage with ignition ON and engine OFF to confirm system supply
Back-probe the injector B connector and observe voltage while commanding injector ON/OFF with a scan tool
Measure injector coil resistance with connector disconnected
Perform wiggle test on harness while monitoring live data or observing code return

Signal parameters

Expected supply voltage to injector circuit with key ON: battery voltage (~12 V nominal)
When injector driver is OFF: driver side (PCM output) should be near battery voltage; when ON it should switch toward ground (close to 0 V)
A persistent low reading (~0–1 V) at the control pin with driver OFF usually indicates a short to ground
Typical injector coil resistance varies by design; many dosing injectors read in the low-ohm range (few ohms to tens of ohms) — consult vehicle/parts spec for exact value

Diagnostic algorithm

Scan and record DTCs and freeze frame. Clear codes and attempt to re-create the fault to confirm reproducibility.
Visually inspect injector B, connector, and wiring for heat damage, pin corrosion, chafing, or physical breaks. Repair any visible damage.
With ignition ON (engine OFF), measure supply voltage at the injector supply terminal and at the injector connector. Verify good battery voltage reaches the connector.
Back-probe the injector control pin. Using a scan tool, command the injector ON/OFF and observe the control voltage. Note whether the driver switches toward ground when commanded.
If the control line reads low while commanded OFF, isolate the circuit: disconnect the injector connector and re-check the PCM output. If the PCM output now measures correctly, suspect the injector or harness. If low with injector disconnected, suspect PCM driver or chassis short.
Measure injector coil resistance with connector disconnected and compare to specification. Replace injector if out of range or shorted.
If wiring suspect, perform continuity checks and insulated resistance tests to identify short to ground. Repair or replace wiring/harness as needed.
Check related fuses, relays and any intermediate connectors/modules. Replace as required.
If wiring and injector check good but problem persists, consult PCM diagnostic data and consider PCM driver failure; only replace PCM after eliminating harness and component faults.
After repairs, clear codes and verify proper operation through multiple drive cycles and confirm no recurrence.

Likely causes

Connector corrosion or damaged wiring near the injector (heat/exhaust exposure)
Short to ground on the injector B control wire
Failed injector solenoid
Faulty PCM driver output (less common)

Fault status

⚠️ Status

Exhaust Aftertreatment Fuel Injector B control circuit low voltage detected. Possible short to ground, wiring/connectors, or injector failure. MIL illuminated.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours