Fault code P20E8 – reductant pressure too low

Fault code P20E8 is called “Reductant Pressure Too Low” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P20E8

Stored code P20E8 means that the Powertrain Control Module (PCM) has detected too low a reducing pressure. This code is only displayed on vehicles with diesel engines.

Fault code P20E8 – reductant pressure too low

Exhaust gas recirculation (EGR) systems are designed to reduce NOx in exhaust gases. But today’s high-powered diesel engines cannot meet strict emissions standards with EGR alone.

Therefore, particulate filters, catalytic converters and NOx traps are also used to deactivate pollutants. Selective catalytic reduction (SCR) systems were invented for this reason.

SCR systems inject a reducing compound (urea) into the exhaust before the particulate filter or catalytic converter. Precisely timed injection increases the temperature of the filter element and allows it to work more efficiently.

This makes the filter element last longer and allows less harmful exhaust gases to be released into the atmosphere.

The entire SCS system is monitored and controlled either by the PCM or by a separate controller that communicates with the PCM. The controller monitors the O₂, NOx and exhaust temperature sensors to determine the appropriate time for reducing agent injection.

The reducing agent feed pump is used to pressurize the DEF system when necessary. The PCM monitors the supply pump voltage for constant fluctuations and load percentage. The PCM also monitors one or more pressure sensors in the restorer supply system to determine if there is a leak in the system.

If the PCM detects that the reducer pressure is too low, code P20E8 will be stored based on the data from the pressure sensors. The Malfunction Indicator Light (MIL) may also illuminate.

Symptoms of vehicle malfunctions

The main signal that an error P20E8 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
  2. Other related fault codes may also be present.
  3. DPF regeneration is disabled.
  4. Decrease in engine power output.
  5. Black smoke coming out of the exhaust pipe.
  6. Increased fuel consumption.
  7. The engine will go into emergency operation mode.

Stored fault code P20E8 should be considered as serious and eliminated as soon as possible. The SCR system may be disabled, causing damage to the particulate filter and catalytic converter.

Factors that can cause this error code

The error code P20E8 can mean that one or more of the following problems have occurred:

  • Defective reducer pressure sensor.
  • Open or short circuit in the sensor circuit.
  • Problem with the restorer control module.
  • Bad electrical connection in the restorer control module circuit.
  • Defective restorer pump.
  • Defective restorer nozzle.
  • Low level of reducing fluid.
  • Problem in the supply lines of the reducing fluid.
  • In rare cases, PCM failure or programming error.

How to fix or reset OBD-2 code P20E8

Some suggested steps for troubleshooting and fix the error code P20E8:

  1. Read all stored data and error codes with an OBD-II scan tool. To find out when and under what circumstances error P20E8 appeared.
  2. Clear the error codes from the computer memory and test drive the vehicle to see if the fault appears again.
  3. If the error code appears again, visually inspect the electrical wires and connectors.
  4. Check the recovery fluid lines.
  5. Visually inspect and test the reservoir pressure sensor.
  6. If necessary, replace the restorer pressure sensor and any defective wires.
  7. Check the restorer control module.
  8. If there are no defects, check the PCM module and its software part.

Diagnose and repair of problems

Before you begin the process of troubleshooting P20E8, you should research the technical service bulletins (TSBs) for your particular vehicle. In some cases, this can save a lot of time by pointing you in the right direction.

Make sure the restorer system is not losing pressure, turn on the pump to create pressure, and check the system for external leaks. Use a fuel pressure tester to check the restorer system manually.

Check the feed pump and injector for leaks, if any are found, they must be repaired before continuing with the diagnosis.

The diagnosis itself should begin with a visual inspection of the restorer system harnesses and connectors. Burned or damaged wiring and connectors must be repaired or replaced before continuing testing.

Using a multimeter, test the power supply to the SCR control system. Check the fuses when the circuit is loaded to avoid misdiagnosis.

Use a multimeter to test the pressure sensors of the restorer system according to the manufacturer’s specifications. Components that do not test within the maximum allowable parameters should be considered defective.

If the reducer feed pump is serviceable, use a multimeter to test the input and output signal circuits from the fuse panel, PCM, and ignition switch. Disconnect all controllers before using a multimeter to test error P20E8.

A common cause of this code is insufficient recovering fluid or failed pressure sensors.

On which vehicles does this problem occur most frequently

Fault code P20E8 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Audi
  • BMW (X5)
  • Citroen (Berlingo, SpaceTourer)
  • Dodge (RAM)
  • Ford
  • Hyundai (Starex)
  • Mercedes-Benz (Sprinter)
  • Peugeot (308, 508, 5008, Traveller)
  • Volvo

Fault code P20E8 can sometimes be found with other errors. The most common are the following: P20E6, P20E7, P20E9.


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