CAN-bus and ElPower script
Introduction
Do you know what diagnostics tool is the most important? Scanner? Oscilloscope? No, that’s not true. Head.
You can say this with complete confidence. No equipment can replace the logical thinking and understanding of the processes that take place in the car. A modern car is a very difficult mechanism. Relying on fault codes is, of course, possible. But after all, no electronic unit has human intelligence and can determine a malfunction code that will lead an inexperienced diagnostician to a deadlock.
Only a person can relate disparate facts, only a person is able to make the right conclusion, based on the data. Unfortunately, we have to admit that not all car technicians are aware of this. Until now, many of them only read the codes with a scanner, without bothering themselves with the search for cause-effect relationships. Such repairs often result in large financial and reputational losses.
Example. We have a car, Infiniti QX70. Engine - V9X 3.0l turbodiesel. The client complained that after a cold start on the dashboard, the all-wheel drive malfunction lamp lights up.
This is the situation when you need to start with a scanner. We connect Consult-III and read fault codes.
Read fault codes
Here you need to understand that all codes that have occurred since the last reset are stored in the memory. Therefore, they should be treated with caution: it may be that the malfunction has long been gone. Or it was some random failure. In especially doubtful cases, it is better to erase all errors, drive a car for a while and only then read the codes again. The information obtained this way will be more reliable.
But, we still read all the codes and try to make the first conclusions. So, many systems have trouble codes. It is alarming that almost all systems contain an indication of a violation of the CAN bus in Figure 1, this car is equipped with:
Figure 1. Systems contain an indication of a violation of the CAN bus
In most systems, these codes are not relevant, but saved. Unfortunately, modern cars have taught us that errors on the CAN bus are almost always present, although in recent years the situation has begun to improve. But in our case, almost all systems “complain” about the bus, that allows us to make the first conclusion: something is wrong with the bus.
The engine control unit indicates another problem with the on-board voltage in Figure 2.
Figure 2. ECU indicates problem with on-board voltage
Pay attention to the anti-lock braking system. Its control unit contains a code not only for the abnormal supply voltage but also for a communication failure on the CAN bus:
Figure 3. Abnormal supply voltage and communication failure on the CAN bus
Experience suggests that first you need to solve the problem with a diagnostic trouble code for the battery voltage.
You know, when it comes to supply voltage, I prefer to test it in the most reliable way: using an angine analyzer. After all, it is necessary not only to measure the value of the voltage, it is important to see and evaluate its shape, to see how it changes over time.
This is actually a very cool thing. For some reason, few people understand the importance of checking the supply voltage and reliability of ground connections with USB Autoscope IV. Very often problems occur with bad power and grounds and cause sporadic defects. Engine analyzer in such situations is a real lifesaver.
Indeed, the trend of recent years is such that manufacturers display less parameters on the scanner. Apparently, guided by the principle of "The Less You Know, the Better You Sleep". This, of course, is a joke. But in fact, recently quite often, without receiving enough information from the scanner, you have to use an engine analyzer. Even on very advanced cars, like this Infiniti.
Diagnostics using USB Autoscope IV
We install the USB Autoscope IV... I almost said “under the hood”, no, in the trunk, because the battery is there:
Figure 4. Connection of the USB Autoscope IV
What next? We run a test called the "ElPower" for automatic analysis of battery voltage and current waveforms. The script in conjuction with the USB Autoscope IV provides an advanced report on the battery, alternator and starter condition. A technician does not even need to think; the program will do everything itself and point to the problem points.
We run the test. It is simple and takes only a couple of minutes. Here are a results:
Figure 5. Results from the ElPower script report
Let's see the results. First of all, the software highlighted in yellow the parameters that do not fit into the tolerance. I would even say that it’s not within tolerance, but generally within reasonable limits!
The initial voltage on the battery is only 11.95 V. This means that the battery is deeply discharged (in fact, the script shows that the battery charge is only 20%).
The recommendation to change the battery is well founded.
And now - the most interesting! The voltage during cranking was ... 7.5 V! It is not just small, it is very small! But the engine is warm, and the starter consumed much less current than when it was cold-started. And accordingly, there was less voltage drop.
It is highly probable that, when trying to start a cold engine, the voltage drop was not up to 7.5 V, but to a much lower value. Apparently, the voltage dropped below the threshold at which the normal operation of the CAN bus is possible. Therefore, the systems contained communication trouble codes.
It would seem that what connection can be between the CAN bus and the ElPower test? It turns out to be the most direct.
Conclusion
Let’s summarize. First of all, you should not rely on the scanner and trouble codes, sometimes this is the way to nowhere. Further, the engine analyzer takes its rightful place at the table of a technician. The most important conclusion: a diagnosis should be based on an understanding of the processes that take place in the car.
And what about the all-wheel drive malfunction lamp? Nothing. After replacing the battery, it no longer lights up.
Authors:
Alexey Pakhomov
Vasyl Postolovskyi
Olle Gladso