P0251 Code:

OBD-II Diagnostic Powertrain (P) Trouble Code

Possible Cause

Possible causes of P0251 include a faulty oxygen sensor, faulty electrical connector at the oxygen sensor, faulty or shorted wiring in the oxygen sensor circuit, a blown fuse for the oxygen sensor (if applicable), low or excessive fuel pressure, a vacuum leak on the engine, excessive exhaust leaks, or a faulty PCM.

Common Symptoms

  1. As the output shaft is turned (by the engine) the electro magnetic output speed sensor uses the spaces between the splines to provide voltage signal interruptions in the circuit
  2. This will help to determine whether or not the malfunction is intermittent. After the codes are cleared, test drive the vehicle to see if the code returns
  3. As the reluctor ring passes by the electro magnetic sensor, the 5-volt reference signal is completed with the protruding metal surfaces
  4. Should all system circuitry and sensors check out and the transmission is in good working order, suspect a faulty PCM but keep in mind that PCM failure is rare and PCM replacement will require reprogramming.

Similar Problems

Fuel And Air Metering
Low Coolant Circuit
Cruise Vehicle Speed/Set Speed Difference Too High

P0251 Troubleshooting

There will also be noise coming from the turning radiator fan and the belt that turn the fan blade. There are a multiple of other belt driven devices under the hood. An engine pulley is mounted to the engine of an automobile and drives all belts. Your car probably has a serpentine belt which is a continuous belt used to drive multiple peripheral devices. Parts or components should not be replaced with reference to only a P0251 DTC. The vehicle service manual should be consulted for more information on possible causes of the fault, along with required testing.

How to turn off P0251 check engine light ?

There are two ways to turn off the check engine light:

A repair technician can do so once repairs have been made.
The OBD II can automatically turn it off when it fails to detect the problem after several diagnostic cycles.

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