What does OBD II code P0601 really mean?

[Akeem]

Hi guys,

I have a question for the experts here that concerns an OBD II fault code.

 

Recently my wife's 2010 Audi A6 began getting hard to start sometimes, and when I took it to a garage to have it diagnosed, it showed OBD II fault code P0106. According to the mechanic there, this code means that I may have to replace all the wiring, or all the computers on the car to fix this code. This mechanic also says there are about 12-15 computers on this model. Can this be true? How is it possible for all the computers, or all the wiring  to fail at the same time?

I have Googled this code myself, but I could not find anything that says all the computers must be replaced. I must admit however that the technical explanations I have found are way above my limited understanding of electronics, so is there anyone here that can explain this problem to me in simple terms? Any help with this will be appreciated. 

[aatish]

For sure it's a case of greedy mechanic man, show it to other mechanic for second opinion or send to Al Nabooda Audi dealer and let them quote you for repair.

[Barry]

Ross Tech website is the best source of information for VAG related codes. They are the guys behind the VCDS software.

 

http://wiki.ross-tech.com/wiki/index.php/16985/P0601/001537

 

Before spending money on an ECU, check the simple stuff first. Battery condition, charging system operation, ECU supply voltage. Could be something as simple as a corroded terminal. Changing entire wiring looms is overkill, far better to isolate the problem and fix it. If it turns out to be a problem with the ECU itself, you might be be able to update the software rather than replace the entire unit. 

[treks]

Hi Akeem,

Code P0601 is bad news, no matter what you drive and the solution is never as simple as checking battery terminals.

This code refers to a breakdown in communication between the various computers and controllers in a car. This communication system is known as the CAN bus (Controller Area Network) and works almost like a miniature internet in the sense that all the computers that control the various functions of a car are in constant communication with each other and the ECU.

Here is a simplified example-

Imagine that the ECU receives a signal from the vehicle speed sensor. Provided that the signal is valid and that the CAN system is in good working order, the ECU will make the signal available to the-

·         cruise control system (if fitted) for speed control purposes,

·         ABS brakes system, which will compare the signal and the actual vehicle speed to information collected from the wheel speed sensors to arm the brake, stability and traction control systems,

·         fuel management system via the throttle position sensor (and others) for the purposes of calculating an appropriate fuel delivery strategy,

·         transmission control system to regulate efficient shifting,

·         and the proximity warning system, among others.

Now here is the biggest issue-

This code does not even identify an area in the CAN system in which the fault may be present. All it does is say that there is a problem somewhere in the system, which means that to find the problem, a mechanic must test each of the several hundred circuits that make up the system individually for ground, reference voltage, continuity, and resistance. Doing this can take a week or more, so it is sometimes cheaper to replace the entire harness.

However, the fault may not be in the wiring, but in any one or more computers/controllers, including the ECU, but the thing is that many controllers cannot be tested reliably. So if the mechanic has a code reader that works on the SAE J1939, GMLAN, SAE J1587, and LIN diagnostic protocols, he might be able to use the freeze frame data to see  which are(s) of the CAN system were affected first. In this way, it may, or may not be possible to trace the defective controller.

Another problem is that some controllers on some cars lose their memory when a breakdown in communication occurs, even if those controllers were not the cause of the problem. This means that while the mechanic is testing each of the hundreds of circuits, he might come across what might seem like defective controllers, while in reality, these controllers may have lost their memories because something else had failed.

So, if the mechanic replaces the wiring harness but the code persists, the fault may be in any of the controllers. Control modules can fail for any number of reasons, and as @Technician correctly says, these causes could include corroded battery terminals, low battery voltages, or charging system issues. However, fixing these issues won't fix the fault in the CAN system.

Code P0601 is perhaps the most difficult code of all to diagnose and repair, and your mechanic is not altogether wrong when he says that he may have to replace all the wiring and computers to fix the problem. It is not that he is greedy or incompetent- it is just extremely difficult to find the problem, and there  is a distinct possibilty that the root cause of the problem may never be found. 

  I am sorry I don't have better news for you. You can try to replace just the ECU, but there is no guarantee that this will solve the problem. You can also try to reprogram the ECU, but again, there are no guarantees. The only logical thing to do is to have the entire wiring harness removed and inspected before you start replacing control modules.

[cyborg]

Treks, I never knew car computer connection can be so complicated and so "stupid" at the same time. What is the point in having a fault code mechanism that doesn't tell what exactly is at fault? At most it need to have some fail-safe mode that if some one critical CAN / ECU / BUS / TRUCK failed then it should stop the car and ask owner to change that one specific component than leaving this ambiguous mess with almost no guarantee. Even more surprising is, that this is coming from Audi on which I have high respect of using most advanced technology to use and inform the car owner all the time.

I have seen the fail-safe mode first time in 1999 in Kenwood home theater system and it trigger automatically to save the whole system and in end that one circuit was replaced in less than 50 USD to fix that system. From 1999 - 2016 and still Car technology cannot implement such measure in automotive computers in 17 years....? Why....?

[treks]

@cyborg, I completely agree with you. One would have thought that it would be relatively simple to design the system so that the fault is pinpointed exactly, but then again if the car makers did that, they would not make any money with repairs.

On a serious note though- the more complicated the electronics on cars get, the more difficult it becomes to design diagnostic systems because the number of feedback loops have to be extended to every controller everytime a feature such as traction control is added. This is almost the same as adding a computer to an office network. When one computer in the network fails, the whole network can crash, and it is not always easy to pinpoint which system in which computer crashed because the entire network is down.

 

[cyborg]

31 minutes ago, treks said:

@cyborg, I completely agree with you. One would have thought that it would be relatively simple to design the system so that the fault is pinpointed exactly, but then again if the car makers did that, they would not make any money with repairs.

Quoted text is the serious note for everyone in money chain to sip their share.