Last month a customer brought in his wife’s 2008 BMW 3.0 X5. He told us the check-engine light was on and the car had a hesitation on acceleration.
The day before, the car also shifted into park when sitting at the entrance ramp of the freeway and then died. After that, the BMW would crank but not start. The customer had to let the car sit five minutes before it would start. He had the car towed to the shop.
We first performed a test-drive to see if we could reproduce the problem. The car hesitated and stalled.
Once the car was back at the shop, we connected it to the intelligent service technical application (ISTA) and ran a complete computer scan of the vehicle. The diagnostic codes that came back: digital motor electronics (DME) 29F5 catalytic converter conversion; DME 29F4 catalytic converter conversion; DME 2A37 valvetronic eccentric shaft plausibility; DME 2A47 valvetronic eccentric shaft sensor plausibility; and DME 2A77 control unit internal fault output stage.
Before testing anything else, we performed a smoke test on the intake system. The test revealed a large vacuum leak at the intake manifold runner. We removed the runner and found a broken seal and broken flap.
We called the customer and suggested replacing the intake manifold runner.
I also told him that we were replacing the intake runner for the stalling problem, but there were still other codes to address.
After replacing the intake runner, we cleared codes and test-drove the car.
Multiple complex failure
During the test-drive, the check-engine light came on again and the car hesitated on acceleration but did not stall. We connected it to the ISTA again and the DME code 2A47 valvetronic eccentric shaft sensor plausibility was back in the system. We then checked and tested the valvetronic system.
The valvetronic system on this BMW is a variable valve timing system, which allows the mechanical camshaft gears, camshafts and valves to phase (move), so the engine timing can change. There are sensors on the camshafts and on the crankshaft to tell the computer the position of all of the camshafts and crankshaft. The computer then calculates all of the data (engine RPM, speed, temperature, throttle position, cam and crank position), so it can correctly set the timing.
Once this is done, the computer commands an eccentric shaft motor to change the position of the eccentric shaft. This eccentric shaft then phases the camshafts.
Upon further review of the car, we found engine oil in the electric shaft
sensor connector. The eccentric shaft sensor was leaking engine oil into the connector.
We checked the eccentric shaft connector and wire harness to make sure the oil did not damage them. We then cleaned the connector and the wire harness. After that, we called the customer and suggested we replace the eccentric shaft sensor.
The eccentric shaft sensor had been updated, so after the replacement we had to calibrate the sensor and reprogram the DME. We then cleared codes again and test-drove the car. The car drove great for approximately 50 miles, but then it hesitated, prompting the check-engine light to go on again.
After scanning the car with the ISTA, we found a new code: DME 2A43 Valvetronic thermal overload protection warning threshold. We looked closer at the valvetronic motor and decided to pull it out of the engine. On inspection, we discovered that the spool gear at the end of the motor was slightly bent.
Next, we performed a resistance check of the wire harness to the valvetronic motor to make sure the thermal overload was not due to high resistance in the wire harness. The wire harness passed the test, so we suggested to the customer that we replace the valvetronic motor.
On even closer examination of the motor, we noticed that the shaft on the inside of the motor was walking (moving) out of position. The shaft was backing out of the motor. When the new motor arrived, we lined them up and found the shaft had walked out 2 millimeters. We then realized that the eccentric shaft sensor had failed and the computer was overcommanding the motor, making it work overtime. Because the eccentric shaft sensor was bad, we could not see the thermal overload code until the sensor was replaced.
This was another example of a multiple complex failure.
Maybe not so much the customer, but I find these types of failures extremely interesting.