WTH How am I Going To Fix This?
I got a call from a mobile mechanic in my area asking me to take a look at a truck that they had just installed a heater core in. He told me that "ever since" he installed the heater core, the vehicle would not start. Before reading the rest of this, take a peek at the pictures attached.
After seeing the hack job done to this truck, I was ready to run away. It had an edge piggyback device. It had multiple DIY installations. The battery cables were badly corroded. It was jacked up.
The first thing I did was scan the vehicle. No communication with the PCM. The cluster proudly displayed "No Bus". I checked all the fuses that were caged. These are the Black and Yellow ones that you pull when the vehicle is being stored. They were all OK. I then checked all the other fuses with a test light. No problem found. I determined there were two ways to go from here. I could locate the splice pack and check the network nodes, or I could check power and grounds. Since the PCM was easy to get to on this model, I opted to look for power and grounds to the PCM. With the wiring diagram I started checking them. I found that the switched power to the PCM was dead. Fuse #9 was responsible for this circuit. A look in the interior fuse box revealed that the fuse was not present. I surmised it fell out when pulling the dashboard free from the body. The repair was far easier than expected.
I was reminded of a few principals.
- Don't assume that all the fuses needed in the fuse box are present.
- Always have a wiring diagram.
- Look for the simple fix even though there is evidence of tampering all around.
- Listen to the customer's "ever since" story for clues.
- Communication problems often are power or ground issues.
Great find!! This missing fuse thing is becoming more and more common.
I spent decades listening to the stories customers would tell me, and the one thing that always stuck out was the "All the fuses are good." story. Which, to me, meant.... go check the fuses against the wiring diagram and fuse locations. It wouldn't be the first time the old missing fuse trick was the issue. Communication with the vehicle is just as important as being a good listener when communicating with the client.
Great Catch Michael!
I had 2 similar this week.
2011 Tahoe: The customer was unplugging wire harnesses to get the service stabilitrak, and CEL to go out (WTH?) and his door locks and windows stopped working...... Removed Fuse 64 for LBEC1 (power supply to half of the interior fuses) and put it in Fuse 65 position for the electric running boards this truck didn't have.
2002 BMW X5: Customer concern was air suspension inactive message on dash, and airbags where deflated, no comm. with EHC module, found no fuse in the slot, customer stated he had been working on it for 4 months..... not sure why he removed the fuse, but the car was all good after I put a fuse in.
So to make sure, we can talk about fuses here but officially the repair operation is "fixed open circuit in EHC module supply".
Awesome find Michael. I got a question. Is there a recent video I can buy from like say "motor age". That is all about network faults like a beginning series and advanced diagnostics. Like case studies. How to really check them. Check the basics and which networks each manufacture uses and how to diagnose them. I need like an entry level then move on to advanced diagnostics. Like where does each manufacture have their splice packs and how to diagnose them. I seen the guy Steve from simply diagnostics on YouTube and wow man he did a great video. He said there will be a part 2 but he's too busy right now. I asked ATG and they said they wont be around here till January for their new network diagnostics seminar. Just wondering if anybody knows something I can purchase and study and share some information if anybody needs help. Thank u
If you search online there are resources about networks. Keywords would be CAN, K-Line, CCD Bus, J1850, LIN, KWP2000. There are more, but that can get you started. Do you have a labscope capable of displaying a network signal? I would use a wiring diagram and start looking at the signals. An easy way is to get an OBDII breakout box. There you have access to different networks to examine. Your labscope can help you understand the different voltages used and a known good network structure.
As far as where the splice packs are, the wiring diagrams will give you a close proximity. I have written a few articles on Linked in with some network diagnostics. I believe some others have put some on this forum as well. It is great to see others want to learn this stuff.
Thank u for taking the time to answer me back. I have a uscope and I dont have a breakout box but will get one from the snap on truck. I like the otc one Keith uses on his videos but anything is better than nothing. Can I still check these signals with a one channel scope. I know I'm limited but it's a start. Will get a scope just haven't made up my mind as to which one and it's not cheap plus my family priorities comes first. But very soon I will have enough to spoil myself with a scope and begin to start my mobile stuff. Something about the difficult diagnostics that usually scares the normal people but since I'm wired I enjoy it and willing to take the challenge. Jjust like u when u seen those wires and how many things are rigged. I actually like those stuff. I'm weird I know 🤣. But thank u guys and I'll get to start digging into this even though I am limited with a one channel scope
The Uscope may read the signals, I am not sure. Carlos or Jorge could tell us. The problem you will have with the 2 wire CAN is that it is really good to see both the hi and the lo signal. They should mirror each other. If they do not, then there is a problem with one of them. The OTC breakout is nice. I have the AESwave one. The CanDo is also worth looking at. I would avoid the tool truck if you can. You just don't get the bang for your buck. BTW what area do you live?
What's up Mike? I live in Jersey. I'll take good advice and stay away from the tool truck and look into the CanDo. If not I'll just get the otc. The colors are nice. Lol. Looks very professional 🤣🤣. The guy at my shop has the old verus and it just crashed. Just wont turn on. He says he's going to get it fixed with snap on but he's on the fence too like why is he going to spend money to get the scanner fixed to make the bosses money and he get nothing. They should pay for it or provide the shop with a scope or scanner. Shop doesn't have that. Cheap people. They just want want want and not put anything out. Pretty soon I'm leaving. Just waiting on the right opportunity. Gotta be ready for that next step and stay ahead of the game I know u know what I mean Sir. Until then its gathering info, watching scannerdanner premium, my ATG books, wonderful techs on YouTube, diag.net and motorage training connect. Thank u Mike
I do much travel and thought maybe we could meet up sometime. I was in Jersey last year training for Sears Auto Centers. Once I got out of the city, Jersey was very nice. I did not realize that there are farms there. I had never been to the Bronx before. What an experience! I love Italian food. I have never had better than a little restaurant right on the border of New York and New Jersey. I don't remember the town. I had training sessions all over that part of the country. I don't expect I will be there anytime soon. I no longer have a contract with the company that sent me.
Yeah that sounds like fun Mike. Whenever u do come by Jersey we can meet up or a training event in the future. Thanx for ur time and I will get my hands on these systems. Take care god bless
There's a series of posts on this website by Bob Augustine about the different network types. It's pretty informative. I've been to the ATG network class and it was great! Definitely go when it comes around!
Holy crap I searched his name and his posts are all about network and reprogramming. Thank u sir. He just did a seminar with TST last month on immobilizer. It was like 3 minutes away from my house and I missed it. Gotta call TST and gotta be notified whenever they come down here again. Didn't know of this highly skilled tech Bob Augustine but now I do thanks to u martin. Thank u god bless
When I had my shop, I specialized in SAAB...... I learned early to check all fuses in multiple ways before spending any time trying to diagnose anything. Fuses that appeared to have NOTHING to do with the circuit I was having trouble with repaired the problem more than once! First things first.....
A trick I started using recently was to put my readers on, and get my mirror and flashlight, and see if any empty fuse slots/cavities have silver on BOTH sides. Many modern cars will not waste metal, so it is a good starting point (some days). Just another trick, not a foolproof diagnostic process obviously. But when you KNOW they have been dicking with it.......