Fault code P20C9 is called “Reductant Control Module Requested MIL Illumination” 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 P20C9
Stored code P20C9 means that the recovery control module has detected a fault, the presence of which, requires the activation of the control lamp. The control lamp should notify the driver that there is a problem with the exhaust system.
Exhaust gas recirculation (EGR) systems are designed to reduce NOx in exhaust gases. But today’s high-powered diesel engines cannot meet the 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 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.
Reductor heaters are used to prevent this fluid from freezing at extreme temperatures. These heaters are usually located in the reducing agent reservoir or in the reducer supply hose.
If the PCM detects a problem in the restorer system, code P20C9 will be stored and the malfunction warning light will illuminate. Some vehicles will require several failure cycles for the instrument panel warning light to illuminate.
Symptoms of vehicle malfunctions
The main signal that an error P20C9 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
- Other related fault codes may also be present.
- Reduced engine power.
- Black smoke coming out of the exhaust pipe.
- Increased fuel consumption.
- The engine will go into emergency operation mode.
Stored fault code P20C9 should be considered serious and corrected 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 P20C9 can mean that one or more of the following problems have occurred:
- The restorer heater is defective.
- Open or short circuit in restorer heater control circuit.
- Defective restorer temperature sensor.
- Problem with the restorer control module.
- Bad electrical connection in the restorer control module circuit.
- In rare cases, PCM failure or programming error.
How to fix or reset OBD-2 code P20C9
Some suggested steps for troubleshooting and fix the error code P20C9:
- Read all stored data and error codes with an OBD-II scan tool. To find out when and under what circumstances error P20C9 appeared.
- Clear the error codes from the computer memory and test-drive the vehicle to see if the fault appears again.
- If the error code appears again, visually inspect the electrical wires and connectors.
- Visually inspect and test the restorer heater.
- If necessary, repair the restorer heater and any defective wires.
- Check the restorer control module.
- 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 P20C9, you should research the technical service bulletins (TSBs) for your particular vehicle. In some cases, this can save you a lot of time by pointing you in the right direction.
The diagnosis itself should begin with a visual inspection of the restorer system harnesses and connectors. Burned or damaged wiring and connectors should be repaired or replaced before proceeding with testing.
Using a multimeter, test the power supply to the SCR control system. Check the fuses when the circuit is loaded to avoid misdiagnosis.
Using a scan tool, activate the restorer heater to check the control circuit output voltage. If the voltage is insufficient, the controller is most likely defective or has a programming error.
When the voltage output is within the parameters, use a multimeter to check the heater element of the restorer. If the heater element does not meet the manufacturer’s specifications, it has most likely failed.
When the fault code P20C9 appears in warm weather, in most cases indicates that a programming error has occurred.
On which vehicles does this problem occur most frequently
Fault code P20C9 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Hyundai (Grand Starex, Starex)
- Isuzu (NPR75)
Fault code P20C9 can sometimes be found with other errors. The most common are the following: P20B9, P20BA, P20BB, P20BC, P20CA.
