You need a working knowledge of the ins and outs of vehicle systems to properly diagnose and treat problems.
When it comes to no start conditions, it is just part of the job. Things happen to vehicles during and after accidents that can render them inert. The key to solving the problem has less to do with throwing a jump box on it than reading the service information to be sure you are not doing damage. To start, let’s look at a few basic triage methods you can use that will give you the information to begin sorting out a problem.
First things first
Use a digital multi meter (DMM) check across the battery leads and see what your available voltage is in the storage device (battery). If you see anything less than 12 volts, the battery is effectively dead. A fully charged battery will read around 12.7. Your problem could simply be that when the starter tries to engage, the load pulls battery voltage too low for the control modules on the network to stay “turned on.” It is very important to not assume that you can throw a battery charger on a battery, turn it up to stun and everything will work. Many battery chargers will rise to more than 17 volts when they are charging, and attempting to start a car could cause Diagnostic Trouble Codes (DTC) to set for overcharge. There are great resources on SearchAutoParts.com for properly charging batteries, but you first will need to identify the battery type. Many late-model cars are using absorbed glass mat (AGM) batteries that require different charging techniques. If you overcharge a Toyota Prius 12 volt battery, you will destroy it (Fig. 1).
By overcharge, we are talking anything more than 3 amps. There are Honda vehicles out there that may have worked perfectly all their life until the battery is discharged and now will require a software update to work properly going forward. Is that customer or insurance pay? The very loud message I am sending is be sure to use your service information and determine what the battery is, sometimes where it is and how the system functions to ensure success.
The no crank, no start
So you have determined that the battery is OK, but there is simply nothing that happens when you turn the key. Not to worry — our service information can rescue us here, too. First, turn the key and see if you are getting lights on the dash. With the key on and the engine not running, you should see pretty much all the lights in a mode called “bulb check.” If not, you have a power interruption (Fig 2).
Perhaps a first responder clipped the battery cable or a master power fuse is damaged. The key here is to determine what the vehicle needs to start. In most late-model cars, the ignition switch no longer carries any power. It is basically a digital demand switch that tells the network what the driver wants to do; start the car, run it or shut it off. Most do not have accessory positions anymore. In most cases when the key is turned or button is pushed, a signal goes out across the vehicle’s network — usually the high-speed controller area network (HS-CAN) — telling the module in charge of security that an approved key is present. If the key is damaged, you could have a problem. Once that recognized key signal is sent, the controller in charge, generally a body control module (BCM), instrument cluster (IC) or power train control module (PCM), authorizes a crank signal to a smart junction/relay box that in turn sends battery current to the starter (Fig 3).
Any problem on the network can cause this chain of events to stop.
Many vehicles have systems integrated into the supplemental restraints system (SRS) that will send a message to the PCM to shut off the fuel pump in an accident. Unlike the old inertia switches that had to be reset, there are simple key and button dances you can do to reset these systems. By the way, the Ford systems like this use the dome light circuit to turn on the in-tank fuel pump and pressurize the system prior to crank so that the high-pressure pump for their gas direct injection system is primed. If the dome lamps do not come on, the fuel pump probably will not either. If the fuel pump does not run, it is likely the SRS has commanded shutdown.
As I have suggested in previous articles, it is wise to collect all DTCs and record them before you do a hard reset on the network with the scan tool. If there is freeze frame data present, you should look at it to know — if the problem is accident related — what was going on at the time.
What it needs to start
Before we go on to no start problems where the engine cranks, let’s review the basic starting requirements of a vehicle. We need adequate battery power, fuel supply with the correct pressure and an ignition system of some sort. The engine must be mechanically sound and free from any reason that it cannot physically turn (like rails smashed into the crank pulley). We need a security system that is not trying to ‘secure’ the car by disabling things, and we need a group of modules all doing their intended electronic symphony in time.
Cranking no start
For the most part, vehicles built in the last few years do not have security systems that allow a cranking no start. Generally speaking, they just won’t crank at all or they will start for a second and die immediately with a flashing security light. This would lead us to believe that if a vehicle is cranking but not starting, we are missing one of the old-school starting requirements: fuel, spark or compression. If an engine cranks irregularly, a mechanical issue is very suspect. You will need a method such as a coil-on plug inductive wand to determine if there is spark present on most late models because the old spark plug tester is not going to work on most coil-on plug applications (Fig 4, 5).
Ford and Toyota have the ability to determine if there is spark built into their scan tools. Most others are going to require a more sophisticated tool and skill set. You can often check a crank and cam sensor signal with a scan tool package pretty easily. If one of these signals is missing, you may have damage to a sensor or wiring since these are usually close to the front of the engine. The idea here is to find a way to check the electrical heartbeat of the ignition system and the fuel injectors quickly and without taking a bunch of things apart. This would be something that your scan tool should do, or you should become proficient with a lab scope. These are new disciplines that are far more worthwhile learning than probing wires to see if there is power on them. If you have a set of injector noid lights, you can see if the injector is receiving a signal. A fuel pressure test will tell you if there is fuel pressure. Once you get to this point, you should have already performed a careful visual inspection for damaged wiring and electrical, but I will remind you in case you have not.
The big picture
The only way to really learn about how each system you work on operates is to get training. This can come from reading service information in a just-in-time fashion, but if you really want to work on a brand of car it is time to join your mechanical service brethren at the many fine classes that are out there to learn the ins and outs of various vehicle systems. Vehicles have become too complex, and the risk of labor hours is much too high to waste time without a good working knowledge of a given system and the necessary tools to perform the functions required to test them. As we tell our customers, those magic scan tools are of no value at all if you don’t have somebody who knows how to wield them.
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