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Home / DTC / P204E — Reductant Pressure Sensor Circuit Intermittent/Erratic

P204E — Reductant Pressure Sensor Circuit Intermittent/Erratic

Detailed page for trouble code P204E.

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P204E

Generic P — Powertrain

Reductant Pressure Sensor Circuit Intermittent/Erratic

Brand: Generic
Type: P — Powertrain
Views: UK: 12 EN: 22 RU: 18
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Page language: EN

Causes

  • Loose, corroded, or contaminated sensor connector
  • Damaged, chafed, or broken wiring in the sensor circuit
  • Failed or failing reductant pressure sensor
  • DEF crystallization or contamination affecting the sensor or port
  • Intermittent ground or poor reference voltage (5 V) supply
  • Intermittent ECM/input module fault or software issue

Symptoms

  • MIL (Check Engine) illuminated with P204E stored
  • Erratic or fluctuating reductant pressure values in live data
  • SCR system warnings or reduced emissions control performance
  • Possible reduced engine power or limp mode if SCR protection triggered
  • Difficulty starting after DEF freezing/melting cycles (intermittent)

What to check

  • Read and record freeze frame data and all related DTCs
  • Monitor live reductant pressure sensor data while key ON and during engine running
  • Wiggle harness and connector while watching live data for intermittent changes
  • Visually inspect sensor connector and wiring for corrosion, damage, or DEF crystals
  • Back-probe connector to confirm 5 V reference, ground, and signal presence
  • Perform continuity and resistance checks on wiring to the control module

Signal parameters

  • Sensor type: typically analog voltage output (0–5 V) proportional to pressure, or module-level CAN message on some systems
  • Typical signal idle/low pressure: ~0.5–1.0 V (system dependent)
  • Typical signal high pressure: ~3.5–4.5 V (system dependent)
  • Reference supply: regulated ~5 V reference from ECM
  • Ground: low-resistance chassis/ECM ground
  • Intermittent fault presents as sudden spikes, dropouts, or noisy/fluctuating voltage or message loss

Diagnostic algorithm

  1. Verify code and related codes. Record freeze frame and check for other reductant/DEF codes.
  2. Using a scan tool, view live reductant pressure sensor data. Note behavior at key ON, engine OFF, engine running, and during system events (e.g., pump activation).
  3. Perform a visual inspection of the sensor, connector and harness for corrosion, DEF crystallization, chafing, or water ingress. Clean/repair as required.
  4. With connector connected, back-probe the connector: confirm 5 V reference, ground continuity, and observe the signal voltage while cycling key and operating the system. Look for intermittent loss or spikes.
  5. Wiggle test the harness and connector while monitoring live data to reproduce intermittent behavior. Isolate the affected section if wiggle causes code or fluctuations.
  6. If intermittent signal persists, disconnect sensor and measure wiring continuity and insulation to ground and power (check for shorts). Repair wiring faults before replacing components.
  7. If wiring and connectors test good, substitute a known-good sensor or bench-test the sensor per manufacturer procedure (resistance/voltage vs pressure) to confirm sensor operation.
  8. If new sensor behaves the same, inspect/control test the ECM input circuit (look for intermittent reference supply, internal ECU faults, or software updates). Consider module reflash or replacement if supported diagnostics indicate.
  9. After repair, clear codes and perform a road or system test to confirm code does not return and system operates normally.

Likely causes

  • Corroded/loose connector at the pressure sensor
  • Damaged wiring (intermittent break or short) between sensor and control module
  • Contaminated sensor (urea/DEF crystals) causing intermittent readings
  • Sensor internal failure

Fault status

⚠️ Status
Reductant Pressure Sensor Circuit Intermittent/Erratic
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

P204A P204B P204C P204D P20A0
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