What Does P204B Mean?
The DEF pressure sensor is providing a reading outside the expected range or is inconsistent with operating conditions. The sensor may be functioning electrically but reading inaccurately.
Common Causes
30%
DEF pressure sensor mechanical failure or drift out of calibration
25%
Crystallized DEF contaminating pressure sensor causing false readings
20%
DEF pump failure causing abnormal system pressure
15%
Restricted DEF lines or filter causing pressure irregularities
10%
Air in DEF system causing pressure fluctuations
Diagnostic Steps
1
Step 1: Monitor live DEF pressure sensor data and compare to normal operating range (typically 70-100 PSI)
2
Step 2: Inspect DEF fluid quality - check for crystallization, contamination, or improper concentration
3
Step 3: Test DEF pump operation and verify it can achieve proper system pressure
4
Step 4: Check DEF filter and supply lines for restrictions or blockages
5
Step 5: Bleed DEF system if air is suspected, then retest pressure readings
Estimated Repair Cost
$200 - $1,200
Parts + labor, varies by vehicle and location
The DEF pressure sensor is providing a reading outside the expected range or is inconsistent with operating conditions. The sensor may be functioning electrically but reading inaccurately.
The most common cause of P204B (Reductant Pressure Sensor Circuit Range/Performance) is: DEF pressure sensor mechanical failure or drift out of calibration
Typical repair costs for P204B range from $200 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive temporarily but improper DEF pressure affects emissions control. Extended operation may trigger engine derate per EPA mandates.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P204B 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
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