Tools used:
- Vehicle information
- Battery charger/tester
- Charging system tester
- Digital multimeter (DMM)
- Thermal imaging camera
- Current tester
There are many things to consider when faced with diagnosing issues on today’s vehicles. Is the problem intermittent? Is the problem easy to duplicate? What system(s) are affected when the issue occurs? And, one of the most important considerations: do I have the correct tools, equipment, and experience to complete the job correctly and efficiently? The answers to these questions can determine if you will be capable of realizing a profit on the job.
In this month’s Tool Briefing, we will look at electrical problems and discuss some must-have tools you need to both diagnose and repair some common – and some uncommon – problems.
One of the more common issues with vehicles is a no-start situation, which often presents as a no crank, no start. Many of these issues can be easily resolved by simply cleaning battery cables, testing the battery and charging system, and replacing any faulty components.
Other problems can be faults within the wiring to the starter or issues within many of the computer-controlled components including various computer modules or anti-theft systems. Due to the many different scenarios that can be computer-related, and the many types of tools necessary to both diagnose and repair these issues, we will save that topic for an article sometime in the future.
This article will focus on more common no start and battery drain issues. A 2007 Acura MDX came into the shop about 18 months ago. The customer stated the vehicle would drain the battery overnight intermittently and would not start.
Step 1 – Perform initial tests, duplicate the issue
Some of the most important pieces of information you need if the issue is intermittent are obtained by talking with the customer to find out the conditions in which the vehicle is operated when the problem arises.
Our customer stated the vehicle would occasionally not start, but a jump start would allow the vehicle to run all day long. The issue seemed to occur more often after driving on a warm day, rather than night driving. Our first test is always a scan of the vehicle to see if there are any codes recorded. You should check every module but pay special attention to any communication (U) codes. Checking for codes in all modules will allow you to determine if there are any issues with the security system that could be the cause of a no-start.
Next would be a visual inspection of the battery and charging system connections. In order to fully inspect battery connections, you should remove the battery cables to make sure there is no corrosion between each cable end and the battery. If there is no corrosion and the connections seemed secure use a battery tester, such as the Associated Equipment Intellamatic Smart Battery Charger and Analyzer, to load test the battery.
If the battery passes the load test, re-connect the battery cables, start the vehicle, and test the charging system using the proper test outlined by the vehicle manufacturer. Keep in mind, a charging system combined with a scan tool may be necessary to test some vehicles.
Once the battery, connections, and charging system have been tested and ruled out, it is time to check for a battery drain. There are many ways to check for a draw, but one of the easiest is to connect a digital multimeter (DMM) between the battery and the negative cable end.
A good way to make sure you do not damage your DMM’s internal fuse is to build a wire clamp with a built-in 5-amp ATC type fuse that you will connect between your DMM and the battery. If there is a high current draw, the ATC fuse will blow and protect the internal fuse. This little modification can save you a few dollars for the fuse, but more importantly, a lot of time by not having to run around trying to locate the internal fuse for your DMM.
If you detect a battery drain of any significance (over the allowable amount listed in your vehicle information source) you will need to locate the source of the drain. The fastest and easiest tool I have found to do this is a thermal imaging camera like the FLIR TG275 or the Launch Tech USA Thermal Imager. When electrical current is flowing, it generates heat. Using a thermal camera on the fuse panel will indicate which circuit is generating heat.
In the case of the Acura, our initial tests found no issues with the connections, battery, or charging system, and just as importantly, no current draw. Taking into account that the vehicle’s owner stated this problem usually surfaced after driving on a warm day, we thought about what systems might be active under those conditions. The first two things that came to mind were the cooling fan and the air conditioning system.
Step 2 – Isolate the issue, repair the vehicle, and validate the repair
We had one of our drivers take the vehicle on a long test drive while using the A/C. When he returned from the drive, we parked the car in a shady place and shut it down. After about an hour we used the thermal imaging camera on the fuse panel again. This time, the A/C compressor relay showed a heat trace. We removed the fuse and used the Fuse Buddy from Electronic Specialties to test the circuit. The Fuse Buddy has a connector that replaces a fuse, and a digital display that shows how much current is flowing through the circuit.
Our Acura showed about 1.5A flowing through the A/C circuit with the engine off. We then disconnected the relay, and the flow of current stopped. We then switched the A/C relay with the horn relay and the current flow remained at 0A, indicating a faulty relay.
Since many times a relay failure can be caused by excessive resistance in the circuit, we felt it prudent to use our DMM to make sure the A/C Compressor clutch did not have too much resistance. Our test did not show any faults in the system. Also, to make sure there was not a system overcharge that could cause extra load on the relay, we used our RRR machine to service the A/C system. The system was not overcharged.
After we replaced the relay and verified the system was functioning correctly, we released the vehicle back to the customer and that was the end of the story – for about 18 months. Then, the customer called us and said the words we all hate to hear: “My car is doing the same thing again.”
When you hear those words, whether it is the day after a repair or 18 months after, we need to respond to the customer in the same manner. “We will take a look at it and let you know what is causing the problem.” Then you start the diagnostic process in the same way you did the initial repair: without making any assumptions.
Step 1 – Perform initial tests, duplicate the issue (again)
Even though this vehicle had not had an issue even remotely the same as we had repaired 18 months earlier, we treated it as a possible warranty/same issue. We started by performing all of the initial tests again, but this time the thermal imager showed no excess heat being generated by the A/C compressor relay or the relays either under the hood or dash.
We connected the Fuse Buddy between the positive battery cable and the battery to measure and test for any current flowing. After connecting the tool, wait whatever period of time is necessary for the vehicle system to recharge any memory functions prior to reading how much current is flowing and determining whether it is within specifications. The test we performed showed a current draw of nearly 2A, well over what is normal.
We have found when we need to isolate the source of a parasitic draw, the Cal-Van Amp Hound 2 is an easy and quick tool to use to locate the source. The Amp Hound consists of a small box with a screen with a digital readout and a pair of test leads. The kit comes with adapters to replace most fuses in order to read how much current is flowing across the circuit. The tool also allows you to connect directly across each fuse without removing it to obtain readings. This can save huge amounts of time when you are trying to determine which circuit has a fault.
After testing, we isolated the current drain to the audio circuit. Naturally, since this vehicle has a premium sound system in it, electrical issues within the system can be caused by numerous components. Components that are utilized in this system go well beyond a radio and amplifier. The steering wheel has buttons that control some functions, the GPS is part of the system, and it is a major part of the CAN bus system. If you are familiar with a CAN bus you’ll know that some problems can show up in one module even if the root cause of the issue is in a different module.
After using the system layout and wiring diagram in Mitchell 1 ProDemand, we used the Real Fix database function in the program. We don’t always use this feature, but in cases like this one, it can save hours of testing components by supplying information from other shops that have had the same issue. Don’t get me wrong, this does not give you a green light to replace the components that a Real Fix solution gave you; it just allows you to start your diagnostic tests at that component, rather than working your way through the entire system.
There were a few posts about the Acura that had the same issue where the repair consisted of disconnecting the handsfree link module. If the flow of current stopped, replace the module.
We replaced the module, retested the system, and found no further issues.
It is important to invest in tools that are engineered to save you time and provide you with accurate and repeatable results. Those tools, along with good information and a logical testing process will allow you to efficiently and correctly repair vehicles. Remember, the primary thing we sell is time. Anything you can do to sell more time will make you more money, especially if it is a time-saving tool.
