2011 Audi A4 with one code for two different issues
I had a 2011 Audi A4 come in with a driveability issue and the initial information I got was this "CUSTOMER STATES THE CAR WILL BOG DOWN GOING FROM FIRST TO SECOND GEAR THEN YOU HAVE TO PLAY WITH THE GAS PEDAL TO GET THE CAR TO GO. WE WILL NEED TO DIAG". Okay, gas light is on, but MMI says I have enough fuel to drive around. Freeze frame data gave me some good info to try to repeat: happened at full temp, around 1500 rpm, with a light load and low speed, and it happened a lot! Oil is at minimum and a little dirty, but at least this one had oil in it. The fault was a P0341 and the Audi fault number was 4113.
My initial drive wasn't long enough, and in the mean time, my SA got some more information about when the client experienced the concern. The vehicle owner was convinced it was a transmission issue, and the check engine light had "just" turned on a couple days ago. There were not faults in the TCM, only the G40 fault in the ECM. Client wanted me to check trans fluid level and condition anyway, so I did, and it was good.
With the new information of it stalling in a stop and go situation when hot, I plugged my U-Scope on pin 2 of the cam sensor and went back out for a drive. I got the car to stumble and actually stall, and the cam sensor dropped immediately out when it happened. Immediate restart and I drove back to the shop. I recommended a cam sensor and it was approved and replaced. I had also recommended more fuel and an extended test drive (gas light still on), but it didn't happen and I had no stumbling or faults return during a similar length test drive after replacing the cam sensor.
A week goes by and the car comes back. Same fault, but no more stalling or stumbling. This time I went straight for the Picoscope and scoped the cam sensor power, signal, ground, and the crank signal so I can watch engine rpm. It finally had enough fuel to drive around a little more, so I was able to experiment with watching when the fault set. Then I set my scope to 500ms/division and started driving. I regularly repeated the stop and go scenario in downtown traffic, and was able to set the fault a couple times. Then I went back to the scope and used the deep measure tool on the camshaft signal and found my issue.
There you are! Just to the left of the center on the screen, there is an inconsistent pattern and checking the high pulse width measurement, I had one at 956 microseconds instead of the normal 4 milliseconds the rest were.
I check the RPM from the crank sensor and it confirms it happens just during that slight acceleration moment experienced in a lot of stop and go traffic.
Well this finding doesn't really match anything that my research on the fault has found. I just see an extremely short drop out of the signal and then it's business as usual. When I got out the rulers, it confirmed that there was no mechanical change in the timing when it happened.
There is one degree difference between those captures and I could find no indication of the VVT actuating right around there. Most of the common causes I was finding for that fault code was a bad sensor (no, mine worked), bad wiring (still good there), and a timing issue. Now I couldn't justify throwing chains at this with those captures. I even had a friend with the same engine and fault that had warranty work done on his 2011 Q5 and the dealer had replaced his intake camshaft. I still couldn't justify any major tear down like that. So I let the car sit.
I was trying to find a reason why this was happening. It was sitting the bay next to me, taunting me. We looked up on carfax when his last oil service was done, and it was 5000 miles ago. It was due, but not the worst I had ever seen and it didn't smell terrible. It was dark and had an aftermarket filter, but it was all there,and I couldn't see a physical timing change in the scope captures.
I recommended an oil change anyway with some BG EPR and MOA treatments. It was something cheap that needed to be done anyway, so I didn't feel bad recommending it.
Other tech changes the oil and adds the MOA. and clears the fault. He goes to pull out for a test drive and the EPC light flashes for a split second. The P0341 is back.
We all go home and I'm still wondering what is wrong with the car.
The next morning the other tech gets there early, clears the fault again, and takes it for a long drive. No fault. I drive it during my lunch. No fault. SA takes it for his lunch. No fault. It gets driven some more and the fault doesn't return and all the readiness is set. I still don't know what's wrong, but it sure wasn't chains or an intake cam! The original driveability concern of stumbling was gone with the replacement of the cam sensor, but the same cam sensor fault was returning.
A friend of mine had a thought that it could have been a slight cam thrust issue while accelerating. Plausible for sure and the next CAEB I have apart I'll have my dial indicator on the cams checking it out. It 100% looked to me like an electrical drop out on the cam sensor since there was no timing change right there.
Any other ideas?
John Thorton had a case study on an 09 CAEB 2.0 where the cam signal was producing similar "drop outs" at times. it ended up being a metallurgy issue with the camshaft/reluctor and the cam had to be replaced.
I did hear about that but wasn’t sure if it was the same engine. I wonder if that’s the reason my friends camshaft had to be replaced? It’s been well o ear another week since the car has been gone, but if it comes back again, there will be a lot of money to spend. The car is a salvage title anyway and he was on the fence about doing anything.
I was going to say, sounds like a magnetic issue with the reluctor.
I'm gunna have to check that case study out. I would never in my life think that could be the cause. Customers really don't understand how crazy diags can be lol.
Hi Hans, great work. Any chance you can post the deep measure psdata file so I can have a look? Simon
Of course! I just uploaded it.
Great Hans! Many thanks for sharing. Great use of the Pico scope. Simon
waht does a mesuring tool cam do diferent ot how do I get there ? I have pico scope but I have not seen taht or what will be the pro to use that function.
Hopefully this article can explain it better than me! It's a standard feature in the Picoscope automotive software.
Hans, did you mean to include the link to this article: picoauto.com/support/viewto… or some other one? Thank you for sharing these awesome captures and very nice use of the DeepMeasure feature.