Fault code P2042 – reductant temperature sensor circuit malfunction

Fault code P2042 is called “Reductant Temperature Sensor Circuit Malfunction” 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 P2042

Stored code P2042 means that the powertrain control module (PCM) has detected a fault in the reducer temperature sensor circuit. This code is only displayed on vehicles with diesel engines.

Fault code P2042 – reductant temperature sensor circuit malfunction

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.

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.

If the PCM detects a fault in the restorer temperature sensor circuit that is out of tolerance, code P2042 will be stored. The Malfunction Indicator Light (MIL) may also illuminate.

Symptoms of vehicle malfunctions

The main signal that an error P2042 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 memorized as a fault).
  2. Other related fault codes may also be present.
  3. Reduced engine power.
  4. Black smoke coming out of the exhaust pipe.
  5. Increased fuel consumption.
  6. The engine will go into emergency operation mode.

The stored fault code P2042 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 P2042 can mean that one or more of the following problems have occurred:

  • The restorer temperature sensor is defective.
  • There is an open or short circuit in the restorer temperature sensor circuit.
  • The heater of the restorer is defective.
  • 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 P2042

Some suggested steps for troubleshooting and fix the error code P2042:

  1. Read all stored data and error codes with an OBD-II scan tool. To find out when and under what circumstances error P2042 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. Visually inspect and test the restorer temperature sensor.
  5. If necessary, replace the restorer temperature sensor and any defective wires.
  6. Check the restorer control module.
  7. 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 P2042, 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.

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

If the actual restorer temperature is within specifications, code P2042 is retained and the sensor in question is operational. Use a multimeter to check the input and output circuits between the temperature sensor and the PCM / SCR controller.

Restorer temperature sensor codes are usually associated with a faulty or disconnected sensor.

On which vehicles does this problem occur most frequently

Fault code P2042 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • BMW
  • Chevrolet
  • Ford
  • GMC
  • Mercedes-Benz (Gelandewagen, Sprinter)
  • Smart

Fault code P2042 can sometimes be found with other errors. The most common are the following: P2043, P2044, P2045, P2046.


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