U0139 Bristol 401 Diagnostic Trouble Code

U0139 Bristol 401 code definition:
U0139 is a kind of OBD-II Diagnostic U-Network Diagnostic Trouble Code for Bristol 401.

U0139 Bristol 401 is described as Fuel System Too Rich, which basically means bank 1's oxygen sensor has detected a rich condition of fuel. This means there's not enough oxygen in the exhaust from too much fuel being delivered into the air and gas mixture for combusion. Other symptoms that may indicate this problem are when the Check Engine Light illuminates and when there is a visible lack of engine power.

Symptoms

Symptoms of a U0139 Bristol 401 diagnostic trouble code may include:
Place of U0139 in engine

Possible Causes :

  • Defective ECU strategies or components will prevent proper regeneration
  • The Mass Airflow sensor is a hot wire that senses the volume of air entering the intake manifold. The computer uses this information to control fuel mixture.
  • An air leak forward of the DPF will change the sensor readings resulting in the code

Common Misdiagnoses

  1. Vehicle Speed Output Circuit Problem
  2. Cruise Control Servo Indicates Low Problem
  3. A/C System High Pressure High Temperature Problem
  4. PCM Stack Overrun Problem
  5. Transmission Control Module Reprogrammable Memory Problem

Repair Processes :

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. If you find a related TSB, the information will often help in diagnosing the code in question as TSBs are crested from many thousands of repairs. Look at the plug wires to make sure they are not burnt or laying on the exhaust.

Process Tips

Diagnostic trouble code U0139 Bristol 401 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 U0139 Bristol 401.

Fortunately, U0139 Bristol 401 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

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