P05ED

What it means

P05ED means the control unit saw the supply voltage to the reductant (diesel exhaust fluid) heater control module outside the expected range. The module that controls the heaters in the reductant tank, pump or lines is not getting a proper supply. The exact limits and whether the fault is high, low or intermittent depend on the make, model and engine.

Symptoms

• Engine warning light or exhaust fluid/SCR warning on the dashboard
• Message warning of reduced performance or a restart restriction countdown
• Reductant not thawing properly in cold weather
• Other reductant heater or SCR system codes stored alongside
• Possible increased exhaust emissions from the SCR system not working fully

Possible causes

• Poor connection, corrosion or damaged wiring in the heater control module supply or earth circuitlikely
• Blown fuse or faulty relay feeding the heater control modulelikely
• Weak battery or low system voltage from a charging faultpossible
• Faulty reductant heater control modulepossible
• Short circuit or high resistance in a connected heater element overloading the supplypossible
• Outdated or faulty control unit calibration where a manufacturer update is known to address itrare

How to diagnose

1. Read all stored and pending codes and freeze frame data, noting battery voltage, temperature and whether the fault is current or intermittent
2. Check battery condition and measure charging voltage with the engine running to rule out a system voltage problem
3. Visually inspect the heater control module, its connector and nearby wiring for damage, water ingress, corrosion or chafing
4. Check the relevant fuses and relays and look for signs of overheating or poor contact
5. Measure the supply voltage and earth integrity at the module connector, with the circuit under load, using the manufacturer wiring diagram
6. Wiggle-test the harness while watching live voltage to find intermittent faults
7. Check the resistance of the connected heater elements against the specification for that model and engine
8. Check for any manufacturer service information or calibration updates relevant to this code on the vehicle

How to fix

• Repair or replace damaged wiring and clean or replace corroded or loose connectors
• Replace any blown fuse or faulty relay only after finding what caused the failure
• Charge or replace a weak battery and repair any charging system fault
• Replace a heater element that is shorted or out of specification
• Replace the reductant heater control module if it is confirmed faulty after supply and earth are proven good
• Apply a manufacturer calibration update only where an outdated calibration is a documented cause

Can I keep driving?

Nearby codes

• P05ECGenericCold Start Injection Timing Performance
• P05EEGenericReductant Pump Supply Voltage Circuit/Open