Error code P20E8 sounds like reductant pressure too low. Often, in programs working with an OBD-2 scanner, the name may have the English spelling “Reductant Pressure Too Low”.
P20E8 datasheet and explanation
A stored code P20E8 means the powertrain control module (PCM) has detected reductant pressure too low. This code is displayed exclusively on vehicles with diesel engines.
Exhaust Gas Recirculation (EGR) systems are designed to reduce NOx in exhaust gases. But today’s high-performance diesel engines cannot meet stringent emission regulations with an EGR system alone.
Therefore, to deactivate harmful substances, particulate filters, catalytic converters, and NOx traps are also used. It is for this reason that Selective Catalytic Reduction (SCR) systems were invented.
SCR systems inject a reducing agent (urea) into the exhaust before the particulate filter or catalytic converter. A precisely timed injection raises the temperature of the filter element and allows it to operate more efficiently.
This allows the filter element to last longer and emits less harmful exhaust gases into the atmosphere.
The entire SCS system is monitored and controlled by either the PCM or a separate controller that communicates with the PCM. The controller monitors the readings of the O₂, NOx and exhaust gas temperature sensors to determine the appropriate timing for the injection of the reductant.
The reductant pump is used to pressurize the DEF system when needed. The PCM monitors the supply pump voltage for continuous fluctuations and load percentage. The PCM also monitors one or more pressure sensors in the reductant supply system to determine if there is a leak in the system.
If the PCM detects that the reductant pressure is too low based on data from the pressure sensors, a P20E8 code will be stored. The Malfunction Indicator Lamp (MIL) may also illuminate.
The primary driver symptom of a P20E8 code is a MIL (Malfunction Indicator Light) illuminated. It is also called Check engine or simply “check is on”.
They can also manifest as:
- The control lamp “Check engine” on the control panel will light up (the code will be written into memory as a malfunction).
- Other associated trouble codes may also be present.
- Disable DPF regeneration.
- Decreased engine power.
- Black smoke from the exhaust pipe.
- Increased fuel consumption.
- The engine will go into emergency operation.
A stored P20E8 code should be treated as serious and rectified as soon as possible. The SCR system can be disabled, causing damage to the particulate filter and catalytic converter.
Reasons for the error
A P20E8 code may indicate one or more of the following problems have occurred:
- Defective reductant pressure sensor.
- Open or short circuit in the sensor circuit.
- A problem with the reductant control module.
- Poor electrical connection in the reductant control module circuit.
- Defective reductant pump.
- Defective reductant nozzle.
- Low level of reducing fluid.
- Problem in reducing fluid lines.
- In rare cases, PCM malfunction or programming error.
How to Repair or Reset DTC P20E8
Some suggested steps to troubleshoot and fix the P20E8 error code:
- Read all stored data and error codes with an OBD-II scanner. To find out when and under what circumstances the P20E8.
- Clear the error codes from the computer memory and test drive the vehicle to see if the problem reappears.
- If the error code reappears, visually inspect the electrical wires and connectors.
- Check the supply lines for the reducing fluid.
- Visually inspect and test the reductant pressure sensor.
- If necessary, replace the reductant pressure sensor and any defective wires.
- Check the reductant control module.
- If there are no defects, check the PCM and its software.
Diagnostics and problem solving
Before starting the troubleshooting process for your P20E8, you should review the vehicle-specific Technical Service Bulletins (TSB). In some cases, this can save you a lot of time by pointing you in the right direction.
Ensure that the reductant supply system is not losing pressure, turn on the pump to build up pressure, and check the system for external leaks. Use a fuel pressure tester to manually check the reductant system.
Check the feed pump and injector for leaks, if found, they must be repaired before continuing with the diagnosis.
The diagnosis itself must be started with a visual inspection of the harnesses and connectors of the reductant system. Burnt or damaged wiring and connectors must be repaired or replaced before continuing testing.
Use a multimeter to test the power supply to the SCR control system. Check the fuses with a loaded circuit to avoid misdiagnosis.
Use a multimeter to test the reductant system pressure sensors according to the manufacturer’s specifications. Components that do not pass the test within the maximum allowable parameters should be considered defective.
If the reductant pump is OK, use a multimeter to check the input and output signal circuits from the fuse panel, PCM, and ignition switch. Disconnect all controllers before using the multimeter to test the P20E8 error.
A common cause of this code is an insufficient amount of recovery fluid or failed pressure sensors.
On what cars is this problem more common?
The problem with the P20E8 code can occur on different machines, but there are always statistics on which brands this error is more common. Here is a list of some of them:
- BMW (BMW X5)
- Citroen (Citroen Berlingo, Space Tourer)
- Hyundai (Hyundai Stareks)
- Mercedes (Mercedes Sprinter)
- Peugeot (Peugeot 308, 508, 5008, Traveler)
Other errors can sometimes be found with DTC P20E8. The most common are the following: P20E6, P20E7, P20E9.