P202A

What the code means

Code P202A points to a fault in the AdBlue tank heater circuit (Reductant tank heater circuit). The heater keeps the urea solution from freezing at low temperatures. The code sets when the DME detects an electrical fault in the heater circuit: an open circuit, a short, or a failed relay.

How the system works

The AdBlue tank has an electric heating element that switches on at low temperatures to keep the solution liquid. It's controlled through a relay and a fuse. If the heater fails, the AdBlue can freeze, which blocks dosing and limits engine power.

Symptoms

• AdBlue warning light comes on in cold weather
• Possible freezing of the AdBlue fluid in the tank
• Reduced engine power (limp mode) if the system can't thaw the solution

Diagnosis and repair

Step 1: Check the heater resistance

• Measure the heating element resistance with a multimeter. Normal value: 2–10 ohms. An open circuit (infinity) points to a failed heater.

Step 2: Inspect the wiring and connectors

• Check the heater wiring and connector contacts for damage, corrosion, or oxidation.

Step 3: Check the fuse and relay

• Locate the AdBlue heater circuit fuse (per the wiring diagram) and test it with a multimeter. Check that the relay clicks when powered.

Step 4: Replace the heating element

• If you find an open circuit in the heater, replace the AdBlue tank heating element.

Step 5: Clear the codes and verify operation

• After the repair, clear the fault code with diagnostic equipment (ISTA/INPA) and check that the heater works in cold conditions.

Secondary problems

Ignoring the fault can let the AdBlue freeze in a cold climate. Frozen solution can't be dosed, which puts the engine into limp mode. Repeated freeze-thaw cycles can damage the AdBlue tank or the dosing pump, turning it into a more expensive repair.