Video Summary
codes 4391 and 4ba1 point to the charge air temperature sensor or related intake hose monitoring.
sensor is located on the intake pipe between the intercooler and the anti-shutter valve on n47/n57 engines.
use a multimeter to check the connector feed (should be ~5v with ignition on) and sensor resistance response to heat/cold.
connector showed ~3.54v (unexpected) and resistance readings were inconsistent—likely a faulty sensor or ECU feed issue.
recommended next step: replace the sensor, then verify live data and clear codes to confirm repair.
the video highlights codes 4391 (charge air temperature sensor signal) and 4ba1, plus a charge air hose monitoring fault that points to the same sensor or related intake plumbing.
the sensor sits on the intake pipe that runs from the intercooler up to the anti-shutter valve (downstream of the intercooler).
with the ignition on, measure the connector feed voltage (should be ~5v); unplug and test sensor resistance with an ohmmeter while applying heat and cold to confirm it changes predictably.
the presenter measured about 3.54v at the feed instead of ~5v and saw inconsistent, fluctuating resistance readings when heating/cooling the sensor—suggesting either a bad sensor or an ECU/feeding issue.
order and fit a replacement charge air temperature sensor, then recheck live data and clear fault codes to confirm the issue is resolved.
"The main codes we're looking at today are 4391 for the charge air temperature sensor signal."
The video focuses on diagnosing issues with the Alpina D3, particularly related to limp mode activation. The presenter drives the vehicle and identifies problems once the engine is allowed to idle, with symptoms of limp mode appearing when acceleration is attempted.
Significant error codes retrieved include 4391 related to the charge air temperature sensor and another concerning the monitoring of the charge air hose.
The presenter points out that these errors may be linked to a sensor located on the intake pipe that runs from the intercooler to the anti-shutter valve. They also mention another code, 4BA1, which is mentioned but not elaborated.
"The charge air temperature read after the intercooler was stuck at 76.93 Fahrenheit."
Upon checking live data, the charge air temperature reading remains constant at approximately 76.93°F (around 26°C), despite various adjustments made to the sensor.
The presenter plans to determine whether the issue lies with the sensor itself or its signal to the ECU. They highlight the lack of specific guidance online for BMW models, but they discover that the plug for the temperature sensor is similar to that of the oil sensor, which can lead to confusion during repairs.
"The first thing we're going to do is take this off and see the plug."
The presenter begins testing the sensor, using a multimeter to measure the voltage from the connector to ensure it is providing the correct voltage to the sensor.
They detect that the connector is supplying around 3.54 volts instead of the expected five volts with the ignition on. The testing process involves comparing connections to ensure they lead to the appropriate ground.
The realization arises that there’s a potential ECU issue due to the unexpected voltage readings.
"It's definitely responding to heat and cold, but I'm not sure it’s working correctly."
The presenter removes the sensor for further testing, setting the multimeter to measure resistance. Initial readings fluctuate, indicating possible malfunction.
By applying heat, the observer notes a rise in readings, suggesting some functionality, but inconsistencies in readings raise concerns about the sensor's reliability.
Testing the sensor in cold water shows it effectively drops in resistance; however, the inconsistent behavior leads to doubts about its operational integrity.
"I think the sensor is damaged; I will order a new one for testing."
The presenter concludes that the sensor is unlikely to be functioning correctly based on the fluctuations and compares expected resistance values for various temperatures.
They plan to order a replacement sensor, stating the OEM part number for viewers who may need it. While unsure of the current sensor's functionality, they look to validate the diagnostics with a new part.
