Output Shaft Speed sensor circuit intermittent failure The output shaft speed sensor signal to the PCM is irregular or interrupted.
Harness connector not properly seated Harness intermittently shorted, or open Harness connector damaged OSS sensor damaged, or not installed properly Verify harness and connector integrity Verify OSS sensor proper installation.
At this point we are assuming that the fuses and relays are good. You will need to locate the PCM/TCM and the power input signal circuit using your vehicle information source. Unplug the connector from the PCM/TCM, place the ignition switch in the ON position, and probe the appropriate circuit with the positive test lead of the DVOM.
Difficulty Level (Easy)
Repair Time (20 Min.)
||Cost Prediction : $ 30-110|
When you turn on the ignition, the Service Engine Soon or Check Engine C3991 light should flash briefly, indicating that the OBD system is ready to scan your vehicle for any malfunctions. After this brief flash, the light should stay off while you drive as long as no problems are detected. If external charging fault so, you'll be glad to know that your vehicle is equipped with an early warning system that could save you time, money, and fuel in addition to helping protect the external charging fault.
C3991 is a kind of Chassis Trouble Code
Diagnosing chassis noises can be one of the most frustrating problems technicians face. Fortunately, manufacturers have engineered noise, vibration and harshness (NVH) diagnostic techniques and equipment to find the source of the noise.
You can view according C3991 DTC for your car model. We selected several models to see obd2 solutions click and view it.
|+C3991 Toyota Alphard||+C3991 American Roadster||+C3991 Railton Straight+8||+C3991 GAZ M-20||+C3991 Steyr 500|