However, I really wanted to prove this to myself. The only conclusion I could come to was that the BCM was somehow shorted internally to ground on the sense circuit. ![]() This was certainly looking more like a bad module than a shorted wire at this point. After disconnecting all of them one at a time I had infinite resistance, and as I disconnected each one I maintained my 1k ohm resistance. Nevertheless I decided to start pulling modules off the line by disconnecting them.Īccording the wiring diagram the only modules on the wake up circuit was the Fuel Pump Control Module, The ABS Module, PCM, and the Transmission control module. The meter showed 1k Ohm resistance, which although is a little low for a communication circuit, it didn't seem like a short to ground for me. My thoughts was that if I had a short to ground that was a problem, I would likely have a pretty low resistance to ground in it. I decided the easiest course of action to test my theory was a simple resistance test. If I saw a dead open I might have been worried, but this was expected. ![]() Now this didn't really mean a whole lot because the circuit was not loaded at this point, so I figured I was likely just seeing path to ground back through the other modules. ![]() This in mind I disconnected the connector at the BCM and using my PowerProbe I saw path to ground on the circuit. The code indicated that the BCM saw a short to ground on that circuit. The BCM receives a communication signal from the PCM when the ignition is turned on. The DTC detection logic of the U1814 states that the BCM will not send out the wake up signal when the code is set, so I figured this is certaily the code I need to chase.Īs with everything electrical, you can always reduce any problem to the most basic electrical circuit. Clearly we were going to have to delve into the communication system on this vehicle.Īfter spending some time doing some research on the communications circuit, I found that the BCM sends out a 12v wake up signal to each of the modules that were not talking on the circuit. I was missing the PSCM, ABS, AWD module, TPMS, etc. I was able to talk to the PCM, TCM, BCM, Antitheft, and SRS system. This vehicle had only the primary modules currently on the network. The subtype for this code was a 02 which is a short to ground condition.Īnytime I deal with CAN communication codes the first thing I like to do is take a tally of who is actually communicating on the network. I pulled codes from the vehicle and had two CAN communication faults in the the Body Control Module that stuck out a U0121 (loss of communication with Electronic Brake Control Module) and a U1814 (Powertain Wake Up Circuit fault). I find that the Verus Edge works very well with most domestic vehicles, and is my goto for a scan tool most of the time. Having come up with nothing during my visual inspection, I decided to whip out the scanner. You could tell that the vehicle was hit pretty hard in both the front and driver's side, but nothing really stuck out as a problem. So I spent a few minutes just combing over the vehicle looking for something obvious. This vehicle being a salvage that was put back together, I expected to find a broken wire somewhere. Preliminary inspection yielded little results. It also displayed "AWD Problem, and "Service Steering System" on the display. ![]() The IPC had multiple lights on, and there was no power steering in the vehicle. Today's patient was a 2017 Chevy Equinox that had been wrecked and put back together. Aaron always calls me with fun ones, and today's project certainly did not disappoint. Last night we got a text from Aaron of AJ's Automotive of Minford Ohio, one our best customers when it comes to advanced diagnostics.
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