P05ED: Reductant Heater Control Module Supply Voltage

Some diesels use a separate control module or power stage for the DEF heaters in tank, pump and lines; without heating, frozen fluid cannot thaw in winter and dosing stays blocked. P05ED reports that this module's supply voltage is outside its allowed window – a blown main fuse, an open feed or ground, or system voltage too low or too high. Chrysler (FCA) lists this code among those that trigger the DEF inducement: a 'Service DEF System' warning, a countdown after 50 miles and no restart after 150 miles (P241D). Thresholds are not published; GM's L5P monitors the comparable heater supply under its own codes and flags a drop of more than 3 V below battery voltage while heating is requested. Start with fuse, feed, ground and battery or charging system.

Symptoms

• Check engine light on
• DEF/AdBlue warning, possibly countdown to no-restart
• In cold weather: DEF frozen, dosing blocked, further heater codes

Most likely causes

• Main fuse or feed wire to the heater module faulty, connector corroded (splash zone)
• Poor module ground
• Weak battery or charging fault (system voltage too low or too high)
• Heater control module faulty internally

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. Look for white crystals around the injector and the tank
3. Check connectors and heaters with the scanner
4. Run the dosing test available on your diagnostic tool
5. Replace parts only when the test points to that component

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P05ED means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 5: Speed and idle
• ED: Specific fault in that system

Frequently asked questions

Can I keep driving with code P05ED?

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

What causes code P05ED?

The most common causes are: main fuse or feed wire to the heater module faulty, connector corroded (splash zone); poor module ground; weak battery or charging fault (system voltage too low or too high).

Related codes

• P05F8Reductant Heater Control Module Performance
• P20B9Reductant Heater A Control Circuit/Open
• P21C2Reductant Heater Relay Control Circuit/Open
• P21CBReductant Control Module Supply Voltage Low
• P0562System Voltage Low
• P0563System Voltage High

Sources

• law.cornell.edu: 13 CCR 1968.2
• static.nhtsa.gov: MC 10184705 9999
• gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
• data.epo.org: document

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.