5V Reference causing stall?
I was called to a shop today with a 2015 Infiniti Q50. This vehicle had rodent damage to the left side MAF (Doesn't contain IAT sensor), and also damage to the main harness next to the intake near the left throttle body. The shop had already repaired all of the wiring damage. No faults were setting and vehicle was taken for a test drive. On the test drive the vehicle hit around 2500 RPM's and stalled. It immediately restarted with a check engine light illuminated reporting a P0340, P0335, and a P0345. Both Camshaft Position Sensors and Crankshaft Position Sensor circuit faults.
Upon interviewing the techs they said originally they had no communication, and the vehicle would not start. They separated the MAF wires that were shorted together (The MAF's are 12V) and the vehicle ran and communication was restored. I duplicated the concern with the vehicle in park. around … RPM's it felt like a slight misfire at times and then the vehicle would stall. I could not duplicate the concern when the faults were present. I also induced a fault by unplugging the MAF that had wiring damage and also could not duplicate the fault. I already had a scope on the vehicle at this point. I never lost ground to either CMP sensor. I concentrated on the 5V at this point. See the attached waveform. The vehicle stalls when the 5V drops out. I am looking for advice before I go back tomorrow. There are no wires shared between these three sensors (although the ECM likely houses a single 5V power supply). I verified with the scope that the 5V sensor power is dropping out on both CMP sensors and I am assuming the CKP sensor as well. The voltage never drops to ground. It never drops below 4.2V when the engine stalls. I want to call it an ECM but when a fault is set the 5V never drops out and the vehicle does not stall. Any pointers would be greatly appreciated.
Are you sure there’s only one 5volt circuit ?
No, however the 5V power supply wires from the ECM to the CMP sensors and CKP sensor are separate from one another. However, they are all affected and drop out as seen in the captured waveform. This is why I suspect there is a common 5V power supply within the ECM.
I wouldn't dare change the ecm. There may be a sensor causing a 5vref short. If i can't be duplicated yes it's more difficult. But i don't see another way to nail it other than ruling out a sensor shorting out the 5v ref
I completely agree, I have eliminated the power steering pressure switch and battery current sensor. Those two sensors are directly shared with the CMP sensors. It made no difference. All I know is It will be extremely hard to tell which sensor is bringing it down If it is a sensor. Every time I induce a fault and the MIL is illuminated the problem is gone. As soon as I plug everything back up
Per troubleshooting for p0345. There are some more sensors listed. Accelerator pedal sensor, EVAP control system pressure sensor and Refrigerant pressure sensor. besides those you have been working with.
Put a low amp clamp on the reference wire (s) and see if current goes up when the voltage drops. Current up, external. No change in current, Internal providing powers and grounds are good. That is the direction pointer, anyway.
That statement right there is diagnostic gold, thank you for that Jim.
I read about this same technique a few months ago in a case study by Brandon Steckler. I found it here. This technique looks to be an easy yet powerful way to hone in on a difficult problem.
Thank you Bob!! I have read almost every post on Diag.net except I hadn’t finished reading this one! DOH!!! I feel confident I will pinpoint the cause.
Bob, I will in no way take credit for the idea, I was introduced to the concept over 15 years ago and do not remember exactly how. I do know this technique has been presented in some CTI classes over the last ten-twelve years at least. I will look to dig up an example and explain some of the details of when and how to look at information. Due to the design of voltage regulators and the use of
Jim, I look forward to reading that. I hope I wasn't stepping on your toes by posting the link to Brandons post. I just thought it tied in nicely to the current thread.
Bob, not at all! That is what this place is all about. If anything it is a reminder about the current reality. A good tip, technique or methodology is good, period. If we have been on forums long enough we have witnessed the long term members get frustrated with repeated questions on the same topics. Sure, search works and should be used, but we also need to remember people are at all
I returned to the Infiniti today to monitor current on the 5V supply circuit as suggested. See the attached waveform. It appears the current drops when the 5V drops out, then current increases, peaks, and returns to normal. this is the first time I have performed this test on a 5V supply. It definitely didn’t increase at time of drop out. I did double check my clamp was oriented correctly
If I recall the same 5volt supply, came out of ecm via more then one pin. So may want to try on other 5volt outs. It's also possible ecm internal shorting or 5volt regulator going bad. Per your p0345 there was acellerator pedal, evap and refridgerant sensors. I would check the other supplies also. Before doing ecm.
Hi Benjamin, Sorry for the delay in getting back to this post, things get lost in the email at times and all we try to follow. The vehicle you have is a little more complex than the simplest vehicle examples we have. There is nothing in service information to say how many (if more than one) and what components share (other than what we can see on the wiring diagrams) supply. The code set
Jim, thank you so much for this outstanding write up. This is great info, and much of it adds up exactly with what i am dealing with. I am not sure if you saw my waveform so I will post it again. As mentioned this car had rodent damage. It would not start or communicate until the wiring damage was repaired (not by me). The stalling is a new symptom that appeared after all of the wire damage was
What wire was this capture taken from and was the clamp zeroed? I saw the Delta measurement at the top so I wondered. If the multiple wires are shared source I guess one could monitor seemingly unequal behaviors. The voltage bump being global but the current flow to parallel circuits seeking to follow a different drum. I was looking over the diagram earlier just on a PC screen. There appeared
I duplicated this capture from both CMP sensors. This particular capture was from the left bank CMP sensor At … rpms. The fault can not be duplicated under 2500 rpms. The clamp was zeroed and I verified it was oriented correctly multiple times with an increase in current at key on. I have printed all of the Engine control diagrams and isolated the circuits. I have unplugged the AC
Hopefully you’ll get to the bottom of this one! I remember a case study or two (one from Eric O.) where harness was moved closer to the coil and the interference at high rpm made the ECM go bananas. Could be something similar happening in your case?
Thank you Dmitriy. I am not one to give up. I will figure it out. I will continue to update everyone with my findings.
Very nice. Those are great captures that really tell the story. What amp clamp did you use here?
Hey Bob, I’m not sure if you are responding to my waveform or those that Jim shared as examples. I used the Pico TA018 60/20A clamp for the captures. I wish I had an even more sensitive clamp for this vehicle since I am measuring mA. It‘s all I have at the moment. I feel there is alot of hash in the signal as well when the engine is running. I tried using the filter with not much improvement.
Unfortunately, I will never know the outcome of this vehicle. Being a one man show mobile Diagnostician and Programmer I am limited on spending tons of time with vehicles like this. I found a donor ECM which changed nothing. I unplugged the AC pressure sensor, no difference. I unplugged the Evap Pressure sensor, no difference. I plugged in a Donor cam sensor and swapped it on both banks. No
Completely understandable! I was thinking this one would be difficult due to the rodent damage and repairs made. Thank you for updating the post. Reality sets in on time vs reward. I am like you and hate to walk away from an unresolved challenge.
Just to update everyone on this post on what the final fix was. This car ended up going to the dealer. They replaced the main engine harness, the sub-harness under the intake, and the ECM. All of this for the price of $8600!! i had already tried a doner ECM which solved nothing. My guess is the main harness still had unseen rodent damage somewhere that was taking the 5V reference down.