AdBlue pump fault vs heater fault – quick roadside checks

Your dash throws up the blue DEF light, the miles-to-no-start count clicks down, and the delivery run to Fenton suddenly looks shaky. Before you panic-order a new tank, spend five minutes with a torch and, if you have one, a multimeter. You might spot whether you’re facing an AdBlue pump fault or an AdBlue heater fault right there in the lay-by.

Dashboard clues you can trust

The van’s ECU is chatty if you know how to listen. Plug in a cheap scan tool or watch the code that pops up on the dash service screen:

• P20E8 / P20E9 – low AdBlue pressure. 9 times out of 10 that’s the pump struggling to prime.
• P13DF – heater circuit open. The fluid is cold and thick; the heater isn’t doing its pre-warm job.
• P204F – overall SCR efficiency. Often shows up as a follow-on when pump or heater performance tanks.

Spot those codes? You’re already halfway to the answer without even lifting the bonnet.

The 5-minute multimeter test

Carry a meter? Good. Pop the driver’s seat, slide the carpet flap, and you’ll see the SCR tank harness.

1. Set the meter to resistance.
2. Probe the heater pair (usually white wires). Anything above 10 Ω and you’ve likely got a broken element.
3. Switch to continuity on the pump pins (yellow/green). No beep? The pump motor windings are open—time for a swap or software workaround.

No meter? Lift the tank cap instead. Thick crystals around the strainer = heater can’t melt frozen urea. Bone-dry strainer while the tank is half full = pump isn’t pulling.

Roadside DVSA checks now include inspections for “emissions cheat devices, including AdBlue emulators”, the traffic commissioners warned in updated guidance on 9 Jan 2024.:contentReference[oaicite:0]{index=0} Fix it before the officer fixes you with a fine.

When it’s software, not hardware

Modern SCR tanks are sealed units. Dealers quote £1,800+ for a replacement pump-and-heater assembly on a Sprinter; supply shortages can add weeks. That’s why many Stoke operators choose a mobile AdBlue delete instead. I plug in Autotuner, edit the SCR map safely, and the countdown disappears before your tea’s gone cold.

Had a full tank, fresh fluid, but the light still pops up? The heater and pump might be fine—it’s the ECU firmware mis-reading pressure. A software reset sorts it without any parts bill.

Last winter on the A50 I reset a Crafter in sleet while the owner sipped coffee in the cab. Twenty minutes later he rolled back to Hanley with no warnings and zero parts replaced.

Can you keep driving?

If the van starts, limp it home, but watch the countdown. Below 100 miles the ECU locks out and you’ll need recovery—or me with a laptop. Ignoring an AdBlue heater fault during a frost can also crack the pump filter housing. That’s £200 you didn’t need to spend.

Still seeing the dreaded “No start in 500 miles” message? Read our step-by-step guide before you switch the key again.