P20F5: Reductant Consumption Too High
What to do
Look under the vehicle for white crystalline deposits around the reductant tank, lines and connections. Reductant dries to an unmistakable white crust, and finding it means a leak — which is by far the commonest cause and the easiest to confirm.
Report any deposits you find. It will save diagnostic time and cost.
Mention how often you are topping the tank up now compared with before. A clear increase confirms the fluid really is being lost rather than the gauge being wrong.
Get a leak fixed promptly rather than just topping up. Reductant attacks paint and some metals, and it crystallises on hot parts — so a small drip left alone can seize components it lands on.
What this code means
The system is using more reductant than the engine's operation says it should.
This is the mirror of the too-low check, and the fluid is going somewhere. The module compares commanded dosing against the tank level falling, and the level is dropping faster than the record accounts for.
Three explanations, and the first is both the commonest and the easiest to confirm.
- A leak. Reductant escaping from the tank, a line, a union or the injector seal. It dries to an unmistakable white crystalline crust, so looking underneath the vehicle finds it in a minute.
- The injector is passing. A needle held off its seat by crystallisation dribbles continuously — so this code very often arrives with a stuck-open injector code, and they are one fault.
- The fluid is weak. Diluted reductant means the system must dose more of it to achieve the same conversion, so consumption rises legitimately while the module compensates. A quality code alongside this one explains it entirely.
The level sensor is the fourth possibility and the innocent one — fluid is not actually being lost, and the gauge is wrong.
A leak is worth finding promptly for reasons beyond cost. Reductant is corrosive to some metals and to paint, and a persistent drip damages what it lands on. It also crystallises on hot components, which is how a small leak becomes a seized part.
Report any white deposits you find; they resolve this diagnosis faster than any tool.
Likely causes
Start here
- Reductant leak from tank or lines · moderate
- Faulty reductant injector · moderate
- Reductant diluted or incorrect fluid · moderate
Less common
- Faulty reductant level sensor · moderate
- Aged or contaminated SCR catalyst · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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