U3979 BMW Fault Code

Description:

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.

U3979 Code Symptoms :

While fuel economy was increased, acceleration was seriously compromised, and the loss of engine vacuum led to a dangerous loss of braking assist when the U3979 code system was in four-cylinder mode. In addition to these issues, while the company proposed a hydraulically controlled system that could be switched from within the car, the version they implemented had to be manually changed in the engine compartment using hand tools.

Diagnosis And Repairing U3979

Parts or components should not be replaced with reference to only a U3979 DTC. The vehicle service manual should be consulted for more information on possible causes of the fault, along with required testing.

How to fix U3979 code ?

• EVAP system hose leaking
• Damaged VCT phaser
• Incorrect Positive Crankcase Ventilation (PCV) hose connection
• Open or short in the VCT circuit

On some transmissions, such as automated manual transmissions or automatic transmissions with manual mode, the GSP switch lets the TCM know whether or not the driver has selected automatic or manual function.

On manual transmissions, the GSP switch informs the TCM which gear the driver is selecting, and may function as a neutral safety switch, depending on system design. The TCM also uses the gate select position switch to monitor transmission operation. For example, if the driver selects manual mode and selects 3rd gear on an automatic transmission, the TCM may monitor speed sensors to detect clutch and brake slippage.