P0021 Mercedes-Benz SC+class Diagnostic Trouble Code

P0021 Mercedes-Benz SC+class code definition:
P0021 is a kind of OBD-II Diagnostic P-Powertrain Diagnostic Trouble Code for Mercedes-Benz SC+class.

P0021 Mercedes-Benz SC+class is defined as Cylinder 3 Injector Circuit Malfunction. This code means the PCM (powertrain control module, also known as ECM or engine control) has detected a problem in the injector or its wiring, or in injector circuit for cylinder 3. The spark should have a light tan color. If the sensor probe comes with white and chalky parts, this means it has been lagging between switching phases, and should be replaced.

Symptoms

Symptoms of a P0021 Mercedes-Benz SC+class diagnostic trouble code may include:
  • Cherry red hot catalytic converter
  • Poor acceleration
  • The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
  • If the DPF is not cleared the ECU will revert to the "Limp Home Mode" until the situation is corrected
Place of P0021 in engine

Possible Causes :

  • A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
  • Faulty IMRC actuator relay (if equipped)
  • An air leak forward of the DPF will change the sensor readings resulting in the code

Common Misdiagnoses

  1. Exhaust Gas Recirculation System Valve 1 Problem
  2. BBV Sensor Circuit Low Voltage Problem
  3. Transmission Engaged At High Throttle Angle Problem
  4. Cruise Inhibit Control Circuit Problem
  5. TFP Valve Position Switch-Drive Without Drive Ratio Problem

Repair Processes :

If the scan tool has that capability, and the scan tool can operate the IMRC valves, then the problem is either resolved and a simple code clearing is all that's left or a new PCM would be called for. Look for missing ground strap or a rusty ground where the fuel tank is grounded to the frame. Check for damage to the wiring harness connector.

Process Tips

Diagnostic trouble code P0021 Mercedes-Benz SC+class is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.

Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before P0021 Mercedes-Benz SC+class.

Fortunately, P0021 Mercedes-Benz SC+class is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

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