Recently, I received a call from a customer whom has never been here before. His vehicle was at the dealer and the dealer told him that he needed a throttle body. This didn’t sit well with him and he felt uneasy about paying the dealer 1400 bucks to change out a throttle body if it wasn’t really the problem.
Recently, we have seen a lot of vehicles coming into the shop that are coming from other shops because other shops can’t find the problem. I’m afraid these cases are going to become the norm soon, because even I have been experiencing challenges diagnosing some of the issues our customers have been having. Even though I have a medal from my military days where I was able to figure out a difficult electrical issues with fighter jets, these cars are ever more complicated. The good news is, electricity has to follow the laws of physics, and once you know the rules, you can play the game intelligently.
The codes present were P112F or P0068 in generic OBD2 format. 2D2E 11566 Angle of throttle valve- intake pipe under-pressure, correlation Bank 2 was the code we read with the ISTA platform(The BMW Factory Scan Tool). This is where it gets a little hairy. In my opinion, I believe the dealer in question, had a novice tech who merely looked at the code, saw the word “throttle” and made an assumption. Now it isn’t only the dealer, I see so-called technicians from Autozone to the manufacturer do the same thing, and it is common for everyone to assume. But it’s never a good idea in the realm of emissions diagnosis.
Now this code occurs when the amount of intake air, which is sensed by the MAF and the intake air pressure sensor, does not correlate with the throttle angle. The DME(engine computer) has a specific calculation for throttle angle, RPM and boost pressure and correlates that with the MAF sensor and the boost pressure sensor. These readings need to be within a specific parameter. When they all don’t match up, the DME sets a DTC(diagnostic trouble code) and turns on the service engine soon light.
This code can be caused by a vacuum leak, a faulty pressure sensor, a bad MAF, a bad turbo, a faulty throttle valve, according to the BMW test plan.
I smoke checked the intake to verify there was no vacuum leak. There was no smoke coming from the intake, so no vacuum leak. I also performed a test of the throttle which concluded with no problems. Watching the pressure sensor values showed that bank 2 was higher than bank 1. I figured with no vacuum leaks and the throttle passing it’s test, the pressure sensor was likely the cause and since the pressure sensor was fairly inexpensive, it was a good idea to replace it and see if it was the problem.
Now some would argue that this is “shotgunning” a part into the car but sometimes you have to make an educated guess. The values indicated incorrect pressure and the labor to switch the known good sensor from one side to the other was more than replacing the perceived bad sensor with a new one.
Upon a test drive the values stayed just as irregular as before and during the test drive, I was thinking about the setup between bank 1 and bank 2 and I had my eureka moment. The major difference between the two banks was the fuel tank vent valve only goes into bank 2, not into bank 1.
There is an easy disconnect point and with the vehicle shut off, the valve should be closed. So I disconnected the line to the vent valve and blew into it. No pressure. I easily blew through the tube. The valve was stuck open.
I ordered a new valve and installed it. The subsequant test drive was much smoother acceleration was much smoother and idle quality was so good I could barely perceive the engine was running. The check engine light stayed off and the second fault code check revealed no codes and all was well.
The customer was informed and extremely excited to know his gut instinct was right yet again. Always follow your gut. It’s usually correct.