P204C: Reductant Pressure Sensor Circuit Low
The P204C code indicates that the reductant (DEF) pressure sensor circuit is reporting a voltage lower than the expected range. This sensor monitors the pressure in the DEF delivery system to ensure proper injection into the exhaust stream. A low circuit signal can be caused by a faulty sensor, wiring issues, or a problem with the DEF pump or control module. This condition can lead to reduced NOx reduction efficiency and may trigger a derate or warning light.
01. Most Common Causes
- Faulty reductant pressure sensor
- Open or shorted wiring in sensor circuit
- Poor electrical connection at sensor or ECM
- Defective DEF pump or control module
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine power or derate mode
- Increased DEF consumption or system warnings
- Poor exhaust emissions performance
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the reductant pressure sensor connector and wiring for damage, corrosion, or loose connections.
Step 3: Using a multimeter, check the sensor signal voltage (typically 0.5-4.5V) at the sensor connector with ignition on; compare to manufacturer specs.
Step 4: If voltage is low, backprobe the ECM connector to check for continuity and shorts in the wiring harness.
Step 5: If wiring is intact, replace the reductant pressure sensor and clear the code.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with this code, as it can lead to reduced engine power and increased emissions. The vehicle may enter a derate mode, limiting speed and performance.
How much does it cost to fix?▼
The cost to fix P204C typically ranges from $50 to $150 for parts and labor, depending on whether the sensor or wiring needs replacement. Diagnostic fees may be extra.