Fault Family System: Powertrain (P-Codes) 7 SAE Codes

Reductant Pressure Sensor

Diagnostic & Technical Explanation

P204A (Reductant Pressure Sensor Circuit) monitors the reductant supply-line pressure sensor that confirms the pump is delivering DEF at the pressure the dosing module expects. A pressure reading pegged low almost always traces to a crystallized or air-locked supply line or a weak supply pump, while a high reading points to a restricted return line or a failing pressure regulator inside the metering unit.

These 7 diagnostic trouble codes share one detection mechanism and one repair path, which is why MechanicDB groups them into a single authored fault family rather than repeating the same explanation 7 times.

Codes in this family (7)

Code	Definition	Repair coverage
P204A	Reductant Pressure Sensor Circuit	3 ranked fixes
P204B	Reductant Pressure Sensor Circuit Range/Performance	3 ranked fixes
P204C	Reductant Pressure Sensor Circuit Low	3 ranked fixes
P204D	Reductant Pressure Sensor Circuit High	3 ranked fixes
P204E	Reductant Pressure Sensor Circuit Intermittent/Erratic	3 ranked fixes
P20E8	Reductant Pressure Too Low	3 ranked fixes
P20E9	Reductant Pressure Too High	3 ranked fixes

What this page does not show

This page publishes the fault mechanism and the code index. The licensed dataset adds, for every one of the 15,886 codes, the full authored repair set (56,729 procedures in total) with the fields deliberately withheld here:

Procedures 2..n after the first-listed procedure
Aftermarket parts cost ranges in USD (est_parts_cost_min/max_usd)
Professional labor-hour estimates (est_labor_hours)
Step-by-step diagnostic and repair instructions
Replacement-part mappings and catalog lookups
6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)

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