Code
P20EA
Generic
P — Powertrain
Reductant Control Module Power Relay De-Energized Performance - Too Early
Views:
UK: 25
EN: 60
RU: 29
AI status
Completed
Completed
100%
Causes
- Intermittent or low battery/charging system voltage
- Blown fuse or faulty relay for reductant control module power
- Corroded, loose or damaged relay socket, connector, or wiring
- Poor ground connection at reductant control module or relay
- Faulty reductant control module or internal relay driver
- Water intrusion or physical damage to module/relay harness
Symptoms
- Malfunction Indicator Lamp (MIL) or SCR/DEF warning illuminated
- Reductant pump or heater stops unexpectedly or does not run
- Reduced engine performance or derate in some vehicles
- Dosing faults and elevated NOx or emissions warnings
- Intermittent operation of aftertreatment functions
- Stored or pending DTCs related to reductant system
What to check
- Scan for P20EA and any related reductant/aftertreatment codes; record freeze frame and freeze data
- Inspect battery voltage and charging system (resting and while cranking)
- Visually inspect fuses, relay, relay socket, connector pins and wiring for corrosion, damage, or looseness
- Check module and relay grounds for tightness and corrosion
- Verify relay operation: listen/feel for click when commanded and measure coil/control voltage
- Capture live data for reductant module power supply and relay control signal during operation or while reproducing the fault
Signal parameters
- Battery/supply voltage at relay input: ~11–14 V (vehicle dependent) when system is energized
- Control signal to relay coil: 0 V (off) / ~12 V or ground-switched (on) depending on vehicle design
- Module supply voltage: stable near battery voltage while relay is energized; sudden drops or opens when de-energized
- Relay coil current: typically tens to hundreds of mA (verify manufacturer spec)
- Pump/heater current draw: several amps when running (verify with clamp meter against spec)
Diagnostic algorithm
- Retrieve all stored codes and freeze frame data. Note when code set and any related codes.
- Check battery state-of-charge and charging system. Repair charging/battery issues first.
- Inspect and test the fuse(s) and main power feed to the reductant control module and relay; replace any blown fuses.
- Visually inspect relay, socket, and wiring for corrosion, water ingress, bent pins, or damage; repair as needed.
- Using a scan tool, actuate the reductant module/relay command while monitoring supply voltage at the relay input and at the module. Confirm relay coil control voltage and contact voltage simultaneously.
- If relay fails to hold, bench-test or swap with a known-good relay of same type and retest.
- Perform resistance/continuity checks on supply and ground circuits between battery, fuse, relay, and reductant module. Repair open/shorts.
- If wiring and relay test good, check the control output from the reductant control module for correct drive (voltage/current). If control output is absent or erratic, suspect module failure or software issue.
- After repairs, clear codes and perform road/load test to attempt to reproduce. Monitor live data for correct relay behavior and module supply.
- If intermittent fault persists and wiring/relay verified, consult manufacturer service info for module reprogramming or replacement procedures.
Likely causes
- Faulty or intermittent power relay (contacts or coil)
- Loose or corroded relay socket/connector or supply fuse
- Weak battery or charging system causing voltage drop
- Open/short in supply wiring between battery/fuse/relay and reductant module
- Defective reductant control module (less likely than wiring/relay issues)
Fault status
Status
Reductant control module power relay de-energized earlier than commanded; interrupted reductant system power.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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