U1955 Mazda Xedos+9 Diagnostic Trouble Code

U1955 Mazda Xedos+9 code definition:
U1955 is a kind of OBD-II Diagnostic U-Network Diagnostic Trouble Code for Mazda Xedos+9.

U1955 Mazda Xedos+9 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. There are two wires dedicated for each coil; one is battery feed which usually comes from the distribution center, and the other one for the coil driver circuit from the PCM. The PCM grounds or ungrounds the circuit to activate or deactivate the coil.

Symptoms

Symptoms of a U1955 Mazda Xedos+9 diagnostic trouble code may include:
  • Faulty or damaged wiring
  • The engine oil will exhibit dilution from the ECUs attempts to increase engine temperature. Some vehicles advance the fuel injection timing slightly after top center to afterburn a small amount of fuel to increase exhaust temperatures. Some of this fuel enters the crankcase. When the ECU determines the necessity to regenerate the DPF, the service life of the oil be shortened significantly
  • Poor fuel economy
  • Rich or lean exhaust
Place of U1955 in engine

Possible Causes :

  • Faulty IMRC actuator relay (if equipped)
  • A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
  • A large vacuum leak would cause a massive amount of un-metered air to enter the intake manifold resulting in an overly lean mixture.

Common Misdiagnoses

  1. Control Module Throttle Actuator Position Performance Problem
  2. Air Conditioning (A/C) Clutch Feedback Circuit High Voltage Problem
  3. Cruise Vehicle Speed/Set Speed Difference Too High Problem
  4. Kick-Down Switch Failed Short Problem
  5. Park/Neutral Postion (PNP) Switch Circuit Engine Torque Signal Circuit Problem

Repair Processes :

Now, clear the codes and test-drive the vehicle to see if the code is reset. 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. Oxygen sensors signal the engine management computer the amount of oxygen present in the exhaust, which is used in determining and controlling the fuel ratio.

Process Tips

Diagnostic trouble code U1955 Mazda Xedos+9 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 U1955 Mazda Xedos+9.

Fortunately, U1955 Mazda Xedos+9 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

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