P20E9: Reductant Pressure Too High
What to do
Ask for the reductant injector to be checked first. High pressure almost always means the fluid cannot get out, and a blocked or crystallised injector is the usual reason — so a stuck injector fault stored alongside this one is very likely the same fault rather than a second one.
Mention the weather if it is cold, since a partly frozen line produces this with nothing broken.
Do not put it off. Pressure above the system's design point works on the seals and joints, and a blockage left alone tends to turn into a leak — which is a larger repair than the original problem.
Look underneath for white crystalline deposits and report any you find, since those would mean a leak has already started.
What this code means
Reductant pressure is above what the system should be able to produce.
High pressure has a shorter and more definite list of causes than low pressure, which makes this the easier of the pair to diagnose. The pump can only build pressure against a restriction — so if pressure is high, something downstream is not letting fluid out.
Which points almost entirely at the injector.
- A crystallised or blocked injector is the dominant cause. It cannot pass its dose, so the pump works against a closed path and pressure climbs. Note this frequently arrives together with a stuck-closed injector code — they are one fault, not two.
- A blocked or kinked line between pump and injector does the same thing.
- A frozen section produces it seasonally, with sound hardware.
- A pressure sensor reading high is the innocent explanation and should be eliminated, but it is the least likely.
The important consequence is that high pressure damages things. Seals and hose joints are the weak points, and a system held above its design pressure develops leaks — which then present as low pressure later, after the original fault has done its damage.
Do not simply clear it and continue. The blockage is not going to clear itself, and each cycle is loading the system further.
Look under the vehicle for white deposits, which would mean the seals have already begun to give way.
Likely causes
Start here
- Crystallised reductant injector · moderate
- Blocked reductant return line · moderate
Less common
- Frozen reductant in the tank or lines · moderate
- Faulty reductant injector · moderate
- Faulty reductant pressure sensor · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P20E9.