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Bringing two vehicles back to consciousness after an accident

Friday, June 1, 2018 - 07:00
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I was recently called to two different shops working on vehicles that would not start after being involved in accidents. It is not uncommon for this to happen, especially if there has been damage to wiring harnesses or possible blown fuses that would render certain operating systems that are vital to cranking or starting a vehicle inoperable. There are a lot of manufacturers that put engine control modules in harm’s way up front in the engine compartment near the radiator or even tuck them in a wheel well. But this was not the case in either of these two vehicles. 

Figure 1
Figure 2

The vehicles in question were a 2016 Jeep Renegade that was hit in the rear with tailgate damage (Figure 1) and a 2017 Mercedes GLC 300 that hit in the front and had minor front-end damage (Figure 2). There didn’t seem to be enough damage to prevent either vehicle from starting. There are many times where certain things must be disconnected in order to properly work on the vehicle, but I always make sure I do a full visual inspection just to see that everything is in order. After my visual inspection, I could see that all of the main harness connections and components were restored to their proper fit and there were no signs of wire damage. There were also no warning messages or icons on the instrument panels that would alert me that something was preventing these vehicles from starting.  

I performed a full vehicle scan on each car, checking all Control Modules on board. This is a vital step to do prior to working on a vehicle so you can get a full evaluation of underlying problems with the vehicle that cannot be determined by a visual inspection. Sometimes there may be codes stored in memory that were not accident related and simply caused during the repair procedures to the vehicle. It is equally important to view and document all the codes. Your next step is to clear out the entire vehicle and see what codes return as “Current Codes.” I did find many trouble codes pertaining to wiring and component failures from both vehicles, but the codes that did remain after clearing these had nothing to do with preventing the vehicles from starting.  

Manufacturers today have found a way to prevent you from starting a vehicle after an accident in order to protect the driver from causing further damage to the vehicle or themselves. This is a safety feature in the event that there is fuel leakage or a short circuit in wiring that could lead to a fire in the vehicle. This method of shutdown puts the vehicle in an “Automotive Coma” state so that you won’t be able to leave the scene of the accident even if you’re able to walk away from the vehicle. Let’s take a close look at each scenario. 

Figure 3

The 2016 Jeep Renegade was able to crank but would not start up, and the four-way flashers were on all the time. This Jeep was equipped with a fire protection system that is initiated by the airbag control module if it senses a rear impact that could possibly cause fuel tank damage. Most of the vehicles today are equipped with sensors that can determine lateral, longitudinal and G-Force impact. This helps controllers on board to determine vehicle positioning as well as direction of impact. Since the controllers are all on a Buss Network (Figure 3), they share information among themselves and a message can be sent from the airbag control module to the body control module (BCM) if a rear collision is detected, and the BCM will in turn command the engine control module (ECM) to put the vehicle in fuel cut-off mode (Figure 4).  

Figure 4
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