P20EB: Reductant Control Module Power Relay De-Energized Performance - Too Late

Here the opposite of P20EA happens: after the reductant control module has finished its after-run and released the power relay, voltage is still present on the switched side, so the relay opens late or not at all. Typical reasons are welded contacts, a control line shorted to ground that keeps the coil energised, or a module that never ends its shut-down. The DEF module, pump and heaters may then stay powered with the engine off, which drains the battery and keeps the system awake. No maker documents P20EB publicly. The check mirrors P068B on the engine module, which Saab's 2011 9-5 diesel derives from the relay control circuit, and Ford's 2023 diesel summary flags a reductant relay voltage above 0 V while the output stage is off (P21C7). CARB requires such SCR components to be monitored.

Symptoms

• Check engine light
• Battery drained after the vehicle has been parked
• DEF pump or relay audible long after switching off

Most likely causes

• Welded or sticking relay contacts
• Relay control line shorted to ground, keeping the coil energised
• Reductant control module or network activity preventing shut-down

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the AdBlue/DEF level and quality, and do not add additives or water
2. Compare the reading with other engine data while varying the engine speed.
3. Look for white crystals around the injector and the tank
4. Check connectors and heaters with the scanner
5. Run the dosing test available on your diagnostic tool
6. Replace parts only when the test points to that component

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P20EB means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 0: Subsystem depends on the code range
• EB: Specific fault in that system

Frequently asked questions

Can I keep driving with code P20EB?

Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

What causes code P20EB?

The most common causes are: welded or sticking relay contacts; relay control line shorted to ground, keeping the coil energised; reductant control module or network activity preventing shut-down.

Related codes

• P20EAReductant Control Module Power Relay De-Energized Performance - Too Early
• P068BECM/PCM Power Relay De-Energized Performance Too Late
• P068AECM/PCM Power Relay De-Energized Performance Too Early
• P21C7Reductant Control Module Power Relay/Relays Control Circuit/Open
• P056DReductant Control Module System Voltage

Sources

• saabwisonline.com: dtc p068a or p068b
• fordservicecontent.com: obd summary diesel 2023
• law.cornell.edu: 13 CCR 1968.2

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.