What Does P204A Mean?
The DEF pressure sensor circuit has an electrical fault preventing proper signal transmission. The ECM cannot monitor DEF system pressure for proper injection control.
Common Causes
35%
Failed DEF pressure sensor with internal circuit failure
25%
Damaged or corroded pressure sensor connector
20%
Open or shorted wiring between pressure sensor and ECM
15%
Loss of sensor power or ground supply
5%
ECM sensor input circuit failure
Diagnostic Steps
1
Step 1: Inspect DEF pressure sensor connector for corrosion, damage, or loose connections
2
Step 2: Check sensor power supply (typically 5V reference) and ground with key on
3
Step 3: Measure sensor signal voltage at rest and compare to specifications
4
Step 4: Test continuity of all wires from sensor to ECM
5
Step 5: If all circuits test good, replace pressure sensor and retest
Estimated Repair Cost
$180 - $700
Parts + labor, varies by vehicle and location
The DEF pressure sensor circuit has an electrical fault preventing proper signal transmission. The ECM cannot monitor DEF system pressure for proper injection control.
The most common cause of P204A (Reductant Pressure Sensor Circuit) is: Failed DEF pressure sensor with internal circuit failure
Typical repair costs for P204A range from $180 to $700, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle remains safe to drive but SCR system cannot regulate DEF injection properly. May cause engine derate and emissions non-compliance if not addressed.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P204A to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions Control - SCR System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
