U3678 Fiat 500 Diagnostic Trouble Code

U3678 Fiat 500 code definition:
U3678 is a kind of OBD-II Diagnostic U-Network Diagnostic Trouble Code for Fiat 500.

U3678 Fiat 500 is triggered when the bank 1 camshaft position sensor doesn't match the signal from the crankshaft position sensor. The PCM then uses this data to provide the right strategies for the fuel delivery and ignition timing of the engine.

Symptoms

Symptoms of a U3678 Fiat 500 diagnostic trouble code may include:
  • Faulty PCM
  • The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
  • Poor acceleration
  • Engine surge
Place of U3678 in engine

Possible Causes :

  • Rusty exhaust systems, cracked exhaust manifolds or damaged or missing gaskets or donuts will cause air leaks.
  • An air leak forward of the DPF will change the sensor readings resulting in the code
  • A large air leak at or near the number one oxygen sensor would also cause a lean mixture.

Common Misdiagnoses

  1. Crankshaft Position Sensor Circuit Performance Problem
  2. TP Sensor Learn Not Complete Problem
  3. Low Coolant Circuit Problem
  4. Cruise Control System - Vehicle Accel Too High Problem
  5. Kick-Down Switch Failed Short Problem

Repair Processes :

Replace the oxygen sensor that is downstream from the catalytic converter on the side of the engine that does not contain cylinder #1. Also, if a oxygen sensor code stating "heater circuit malfunction" the sensor has most probably failed. If all testing has passed so far yet you still have the same code, check your scan tool and see if it can open and close the IMRC valve. Look for damage to the tank indicating impact that may have damaged the fuel pump or sender.

Process Tips

Diagnostic trouble code U3678 Fiat 500 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 U3678 Fiat 500.

Fortunately, U3678 Fiat 500 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

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